Diffusion MRI

14:00         3964.     Validating Validators: An Analysis of DW-MRI Hardware and Software Phantoms

Paulo Rodrigues¹, Vesna Prckovska¹, W. L.P.M. Pullens², Gustav J. Strijkers³, Anna Vilanova¹, Bart M. ter Haar Romeny¹

¹Biomedical Image Analysis, Eindhoven University of Technology, Eindhoven, Noord Brabant, Netherlands; ²Maatricht Brain Imaging Center, Maastricht University, Maastricht, Limburg, Netherlands; ³Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Noord Brabant, Netherlands

Diffusion Weighted MRI techniques such as Diffusion Tensor Imaging (DTI) and High Angular Resolution Diffusion Imaging (HARDI) are emerging MRI techniques able to depict in-vivo brain’s connectivity map. There is a wide range of uses of these techniques; however, their application in a clinical setting requires thorough validation. This work aims to validate DTI and HARDI software phantoms, in regions of single and complex fiber bundles, w.r.t to hardware phantom and in-vivo human brain data. Knowledge of the accuracy of synthetic data can improve the evaluation of such algorithms, and advance the employment of DTI and HARDI into clinical environment.

14:30         3965.     Diffusion Imaging and Tractography on a Hardware Model of the Human  Optic Chiasm

Wilhelmus LPM Pullens¹, Alard Roebroeck¹, Rainer Goebel¹

¹Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Limburg, Netherlands

The human optic chiasm is an interesting, complex fiber structure, hard to image in vivo. Based on the anatomy, a DW-MRI phantom was constructed, offering the possibility to quantify tractography results, with little limits on imaging time, and it does not suffer from motion or cardiac pulsation artifacts. A detailed analysis of Constrained Spherical Deconvolution and tensor reconstructions was done, as well as quantitative (probabilistic) fiber tracking. These phantoms form ideal test objects to improve and validate imaging and quantitative DW-MRI tractography on complex fiber structures such as the optic chiasm.

15:00         3966.     Diffusion Properties of Cortical Layers in Fixed Human Brain Tissue Investigated with High-Resolution STEAM

Ana-Maria Oros-Peusquens¹, Arlad Roebroeck², Oleg Posnansky¹, N Jon Shah^1,2

¹Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Forschungszentrum Juelich GmbH, Juelich, Germany; ²Faculty of Medicine, JARA, RWTH Aachen University, Aachen, Germany

MRI of fixed tissue can be performed with very high resolution since measurement time is not a major constraint. Here, we use STEAM diffusion to overcome EPI-related problems (poor resolution, distortions, signal drop out) at 9.4T. We investigate fixed tissue samples from the occipital lobe (visual cortex) and temporal lobe (auditory cortex) with a voxel size of 80nl (resolution of 0.3x0.3x0.8mm). Cortical layer structure is observed in the ADC and FA maps. Fibre tracks from the stria of Gennari, from adjacent white matter and fibres emerging from the grey matter joining the regular tracts of the white matter are investigated.

15:30         3967.     Nanotubular Superparamagnetic Probes as Contrast Agents for Diffusion Tensor Magnetic Resonance Imaging

Viviana Negri¹, Arisbel Cerpa², Laura Nieto³, Pilar Lopez-Larrubia³, Sebastian Cerdan³, Paloma Ballesteros⁴

¹Organic Synthesis and Molecular Imaging Laboratory, UNED-CSIC Unit, Madrid, Spain; ²Universidad Europea de Madrid, Madrid, Spain; ³Animal Models of Human Disease, IIBM-CSIC, Madrid, Spain; ⁴Orghanic Synthesis and Molecular Imaging Laboratory, UNED-CSIC Unit, Madrid, Spain

Single Walled Carbon Nanotubes (SWNT´s) prepared by Chemical Vapor Deposition, oxidized with nitric acid during 48h, depicted 100-200 nm length and contained the paramagnetic metals (17% Ni, 4% Y). Orthogonal water ADC measurements performed in a suspension of SWNT´s in sodium dodecylbenzenesulfonate (2%), with the diffusion encoding gradient oriented in the H-F, L-R or A-P directions,  showed significantly higher water ADC´s in the H-F direction than in the perpendicular plane.  These results suggest that ADC values of tissue water may be modified anisotropically using these preparations, opening a new perspective for contrast agents active in ADC weighted MRI.

13:30         3968.     Non-Parametric Deformable Registration of High Angular Resolution Diffusion Data Using Diffusion Profile Statistics

Pew-Thian Yap¹, Yasheng Chen¹, Hongyu An¹, John H. Gilmore², Weili Lin¹, Dinggang Shen¹

¹Department of Radiology, University of North Carolina, Chapel Hill, NC, United States; ²Department of Psychiatry, University of North Carolina, Chapel Hill, NC, United States

We propose a full-brain multi-scale feature-based deformable registration algorithm based on the statistics of the diffusion profile of HARDI data. Besides the advantage of avoiding any predetermined models which may not necessarily fit the data, our method registers the diffusion weighted images (DWIs) and allows model fitting after the registration. This essentially means that our method can be utilized as a preprocessing step for a wide assortment of available diffusion models. Our method is also well suited for clinical applications due to its low computational cost – around 5 minutes on a 2.8GHz Linux machine (without algorithm optimization) to register a pair of images of typical size 128 x 128 x 80. The main idea involves extraction of statistical features directly from the diffusion profile, which includes mean diffusivity, diffusion anisotropy, regional diffusion statistics, and statistic-map-based edges.

14:00         3969.     Symmetric Diffeomorphic Normalisation of Fibre Orientation Distributions - not available

David A. Raffelt^1,2, J-Donald Tournier^3,4, Jurgen Fripp¹, Alan Connelly^3,4, Stuart Crozier², Olivier Salvado¹

¹The Australian E-Health Research Centre, CSIRO, Brisbane, QLD, Australia; ²Department of Biomedical Engineering, University of Queensland, Brisbane, QLD, Australia; ³Brain Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, VIC, Australia; ⁴Department of Medicine, University of Melbourne, Melbourne, VIC, Australia

Fibre Orientation Distributions (FODs) computed by Constrained Spherical Deconvolution can resolve multiple fibres within a single voxel. We have developed a symmetric diffeomorphic registration method to exploit crossing fibre information provided by FODs to spatially normalise high angular resolution diffusion weighted imaging data. We demonstrate the utility of the proposed method by generating a group average FOD template.

14:30         3970.     Diffeomorphic Image Registration of Diffusion MRI Using Spherical Harmonics

Xiujuan Geng¹, Hong Gu¹, Wang Zhan², Wanyong Shin¹, Yi-Ping Chao³, Norbert Schuff, Ching-Po Lin⁴, Yihong Yang¹

¹Neuroimaging, National Institute on Drug Abuse, NIH, Baltimore, MD, United States; ²Department of Radiology, University of California, San Francisco; ³Department of Electrical Engineering, National Taiwan University, Taiwan; ⁴Institute of Brain Science, National Yang-Ming University, Taiwan

We propose a novel diffeomorphic registration method for diffusion MRI data by mapping their orientation distribution functions (ODFs) represented with spherical harmonics (SHs). The registration is based on optimizing a diffeomorphic demons cost function. ODF reorientation is performed by rotating the SH coefficients to maintain the consistency with the local fiber orientations. Rotation on SH coefficients avoids the estimation of principle directions which has no analytical solution and is time consuming. The performance was tested using different SH orders. Results show that registration with higher orders improves the registration accuracy in terms of smaller similarity error and higher directional consistency.

15:00         3971.     Fast Feature-Based Multi-Scale Registration of HARDI Data Using Fourth Order Tensors

Pew-Thian Yap¹, Yasheng Chen², Hongyu An², John Gilmore³, Weili Lin², Dinggang Shen²

¹Department of Radiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States; ²Department of Radiology, University of North Carolina, Chapel Hill, NC, United States; ³Department of Psychiatry, University of North Carolina, Chapel Hill, NC, United States

Fourth Order Tensors (FOTs) give elegant mathematical properties akin to that of the second order tensors. Recent formulation of FOT imposes positivity on the estimates to ensure soundness in a physical sense - a property not often found in more general higher order tensor approximations. Employing FOTs, we propose a fast feature-based multi-scale registration algorithm for whole brain HARDI data. Our registration algorithm requires a low computation cost – 5 minutes to register a pair of 128x128x80 images at 2mm isotropic resolution – making it practically feasible for clinical applications. Our methods involve three major components: 1) Generation of FOT-based features, 2) Hierarchical correspondence matching, 3) Dense deformation field estimation, and 4) Retransformation.

13:30         3972.     Bias Free Estimates of the Diffusional Kurtosis in Two Minutes: Avoid Solving the Kurtosis Tensor

Jimmy Lätt^1,2, Markus Nilsson², Sara Brockstedt³, Ronnie Wirestam², Freddy Ståhlberg^2,4

¹Center for Medical Imaging and Physiology, Lund University Hospital, Lund, Sweden; ²Department of Medical Radiation Physics, Lund University, Lund, Sweden; ³Radiation Physics, Lund University Hospital, Lund, Sweden; ⁴Department of Diagnostic Radiology, Lund University, Lund, Sweden

Diffusion kurtosis imaging provides additional information as compared to diffusion tensor imaging. Due to the long scan times, required to solve the kurtosis tensor, diffusion kurtosis measurements are not always clinical feasible. In this study, we show that a bias free kurtosis value can be estimated through an optimized encoding scheme within a clinically feasible time of two minutes.

14:00         3973.     Influence of Maximal B-Value, Fit Polynomial and Number of Diffusion Directions on the Measured Kurtosis: A Phantom Study

Tristan Anselm Kuder¹, Bram Stieltjes, Amir Moussavi¹, Frederik Bernd Laun¹

¹Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

The diffusion kurtosis is obtained by fitting a polynomial to the logarithmic diffusion weighted signal acquired at different b-values. The aim of this study was to evaluate factors influencing the measured kurtosis. A strong dependence on the maximum b-value and the fitting polynomial was found. The cubic fit does not eliminate the dependence on the maximum b-value and causes a larger uncertainty in the measured kurtosis values compared to the quadratic fit. Thus, the quadratic fit is preferable. Fitting the Diffusion Kurtosis Tensor with 15 directions is unstable and at least 30 gradient directions should be used.

14:30         3974.     Robust Estimation of Kurtosis and Diffusion Tensors in Diffusional Kurtosis Imaging

Ali Tabesh¹, Jens H. Jensen¹, Babak A. Ardekani², Joseph A. Helpern^1,2

¹Radiology, New York University School of Medicine, New York, NY, United States; ²Medical Physics, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY, United States

The diffusional kurtosis imaging model of non-Gaussian water diffusion is parameterized by the diffusion and kurtosis tensors, which are typically estimated via unconstrained least squares (LS) methods. Unfortunately, these methods do not necessarily produce physically and biologically plausible tensor estimates. We address this drawback by formulating the estimation problem as linearly constrained linear LS. Comparison of in vivo mean kurtosis maps obtained using the proposed formulation and unconstrained linear LS highlights the improved estimation quality. The proposed formulation achieves comparable map quality with fewer gradient images than the unconstrained LS approach, offering a savings of 38% in acquisition time.

15:00         3975.     Improving the Fit of the Diffusion Kurtosis Tensor by Emphasizing the Directions of Restricted Water Motion

Tristan Anselm Kuder¹, Bram Stieltjes, Amir Moussavi¹, Frederik Bernd Laun¹

¹Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

The Diffusion Kurtosis Tensor (DKT) describes the directional dependence of the kurtosis which quantifies non-Gaussian diffusion. The aim of this study was to evaluate the quality of the tensor determination under well-defined conditions using diffusion phantoms. The DKT was determined using two methods. While the standard method using a pseudoinverse matrix fails, the new method emphasizing the high kurtosis values allows a reliable fit of the DKT. Comparison of the measurement using 30 directions to that with 256 directions shows the high quality of the tensor model when combined with the improved calculation method.

13:30         3976.     High-Resolution DTI Tractography of the Spinal Cord with Reduced-FOV Single-Shot EPI at 3T

Emine Ulku Saritas¹, Greg Zaharchuk², Ajit Shankaranarayanan³, Murat Aksoy², Roland Bammer², Nancy J. Fischbein², Maxwell Boakye⁴, Dwight G. Nishimura¹

¹Department of Electrical Engineering, Stanford University, Stanford, CA, United States; ²Department of Radiology, Stanford University, Stanford, CA, United States; ³Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States; ⁴Department of Neurosurgery, Stanford University, Stanford, CA, United States

There is much interest in extending diffusion tensor imaging (DTI) research to the spinal cord, whose connections are responsible for motor and sensory functions of the body. However, DTI of the spinal cord is limited by the need for high spatial-resolution, as well as the difficulties associated with susceptibility differences, field inhomogeneities (especially at 3T), and motion of the cord. A reduced field-of-view (FOV) method using a 2D echo-planar RF excitation has recently been shown to overcome these limitations and improve spinal cord diffusion-weighted imaging. This study addresses the application of this method to acquire high-resolution low-distortion DTI (including both fractional anisotropy (FA) maps and fiber tractography) of the spinal cord at 3T.

14:00         3977.     Differences Between Bipolar Disorder Patients and Control Subjects Using a New SPM Toolbox for Track-Based Spatial Statistics

Jadwiga Rogowska¹, M Lopez-Larson², M Bielecki³, Piotr Bogorodzki³, D Yurgelun-Todd²

¹Brain Imaging Center, McLean Hospital/Harvard Medical School, Belmont, MA, United States; ²The Brain Institute, University of Utah, Salt Lake City, UT, United States; ³Institute of Radioelectronics, Warsaw Technical University, Warsaw, Poland

Human imaging studies have implicated structural and functional abnormalities in patients with bipolar disorder. In this study we examined the differences in diffusion tensor imaging (DTI) data between bipolar patients and healthy control subjects using the methodology of Track-Based Spatial Statistics and our newly developed SPM's Toolbox. We found that bipolar disorder patients had significantly lower fractional anisotropy values within the cingulate gyrus when compared to control subjects. Our findings suggest that DTI techniques can highlight microstructural abnormalities in the brain, not evident on conventional MRI, which may be associated with the neuropathology of this disorder.

14:30         3978.     Functional Diffusion Map Evaluation of Perihematomal Edema as an Imaging Biomarker for the Early Prediction of Primary Intracerebral Hemorrhage Outcome - not available

Yuan-Hsiung Tsai^1,2, C-P Lin^2,3, L-M Hsu², H-H Weng¹

¹Diagnostic Radiology, Chang Gung Memorial Hospital, Chiayi, Taiwan, Taiwan; ²Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taipei, Taiwan, Taiwan; ³Neuroscience, National Yang Ming University , Taipei, Taiwan

This prospective study described diffusion change in perihematomal edema during acute stage (within 7 days) after primary intracerebral hemorrhage by using functional diffusion map (fDM). fDM allows a spatial, voxel by voxel tracking of changes in ADC values over time that more precisely reflect the pathophysiological heterogeneity within the edema. Using fDM to evaluate the perihematomal edema appears promising in this study. fDM is feasible in predicting clinical outcome of ICH patient during acute stage.

15:00         3979.     MRI of Acute (<6 Hours) Ischemic Stroke Patients: A Comparison Between Diffusion-Related Parameters

Frank Peeters¹, Dennis Rommel¹, Andre Peeters², Cecile Grandin¹, Guy Cosnard¹, Thierry Duprez¹

¹Medical Imaging, Université Catholique de Louvain, Brussels, Belgium; ²Neurology, Université Catholique de Louvain, Brussels, Belgium

The value of PW- and DW-related parameters for accurately predicting the ischemic penumbra at initial MR work-up in hyperacute stroke patients has remained probabilistic. In the frame we compared parameters obtained from DTI (2-points ADC, mono- and bi-exponential fits) and q-space imaging (tensor analysis) in a short preliminary cohort of seven hyperacute (<6 mours) stroke patients. Initial data analysis enhanced the value of using high b-values for stroke work-up. Anisotropic diffusion and QSI analysis added significantly to standard isotropic DWI and may have the potential to discriminate between worsening vs regressive infarction, and to delineate ischemic penumbra at admission work-up. 

Diffusion in Normal Volunteers

14:00         3980.     The Reconstruction of Hippocampus Network by QBI Tractography

Rung-Yu Tseng¹, Yi-Ping Chao¹, Ke-Hsin Chen¹, Ching-Po Lin¹

¹INSTITUTE OF NEUROSCIENCE, NATIONAL YANG-MING UNIVERSITY, TAIPEI, Taiwan

The hippocampus (HC) is one of the core regions in the limbic system. The function of HC was found to be related to some deficits in some psychological disorders. A current issue on HC is, however, the lack of the evidence to map appropriately between valid structure connectivity and the functional connectivity. In this study, Q-Ball Imaging (QBI) tractography technique was employed to provide advanced information in structural connectivity. On the other hand, resting-state functional Magnetic Resonance Imaging (rfMRI) brought the information of functional connectivity of HC. The combined information facilitates to understand the mechanism of HC clearly.

14:30         3981.     A DTI Study of Developmental Brain Changes During Puberty

Jee Eun Lee¹, Nicholas Lange², Frances Haeberli¹, Richard J. Davidson¹, Andrew L. Alexander¹

¹Waisman Center, University of Wisconsin, Madison, WI, United States; ²Neurostatistics Laboratory, Belmont, MA, United States

DTI measures of normal children during their pubertal period were investigated. When age was matched for the pre-adolescence group (Tanner score 1) and adolescence (Tanner score 3&4) group, there was no significant DTI measures between these groups. However, DTI measures showed strong correlations with age for the entire subjects. Our study may indicate that changes in DTI measures over age are not driven by puberty-related changes directly.

15:00         3982.     The Impact of White Matter Growth on the Maturation of Information Processing and Reaction Time

Nadia CF Scantlebury¹, Conrad Rockel¹, William Gaetz², Nicole Law¹, Don Mabbott¹

¹Program in Neuroscience and Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada; ²Biomagnetic Imaging Laboratory, Children's Hospital of Philadelphia, Philadelphia, PA

Here we use the latency between a visual cue and a motor response to measure reaction time and test the contributions of white matter on information processing in children. Combined MEG and DTI methods were employed to delineate tracts that are likely involved in the modulation of signal transmission for reaction time.  Findings implicate the white matter integrity of the inferior fronto-occipital fasciculus and the cortico-spinal tracts as important players in modulating reaction time.  Age-related changes in white matter organization of these tracts are likely involved in increasing the efficiency of signal transmission and information processing.

15:30         3983.     Dexterity and Age Relate Differently to White Matter Organization in Cervical Spinal Cord in Healthy Subjects

Påvel Lindberg¹, Antoine Feydy², Marc A. Maier³

¹Radiology B, Hopital Cochin, Paris, France; ²Radiology B, Hôpital Cochin, Paris, France; ³LNRS, Universite Paris Descartes, Paris, France

We hypothesized that spinal white matter organization relates to the level of dexterity in healthy subjects. Spinal white matter was analyzed using DTI and related to a precision grip tracking task. FA was lower in subjects with high tracking error and decreased with age. The closest relation between FA and tracking error was found in the lateral spinal cord whereas FA of the medial spinal cord correlated with age. The results suggest (i) a functionally relevant specialization of lateral spinal cord white matter and (ii) an increased sensitivity to age-related decline in medial spinal cord white matter in healthy subjects.

13:30         3984.     A Probabilistic White Matter Atlas Approach to Assessing Age Related Changes in the Brain

Emma Claire Robinson^1,2, Fani Deligianni^1,2, Alexander Hammers², Daniel Rueckert¹, A. David Edwards²

¹Department of Computing, Imperial College, London, United Kingdom; ²Clinical Sciences Centre, Imperial College, London, United Kingdom

This abstract presents a study of fractional anisotropy (FA) variability in tracts passing from anterior to posterior regions of the brain during healthy ageing. Tracts are propagated in a common-co-ordinate space using a probabilistic white matter atlas. This is constructed by transforming uncertainty distributions on the principle diffusion directions for each subject to a common co-ordinate space and combining to generate a distribution for the population. FA is compared all voxels along the tract using permutation testing. Studying tracts in this way allows direct visualisation of FA changes along the full length of the tract

14:00         3985.     Development of a WM Atlas Based on Anatomical Connectivity Mapping

Mara Cercignani¹, Karl Embleton², Geoff J. M. Parker³, Marco Bozzali¹

¹Neuorimaging Laboratory, Santa Lucia Foundation, Rome, Italy; ²Cognition and Cognitive Neuroscience Group, School of Psychological Sciences, University of Manchester, United Kingdom; ³Imaging Science & Biomedical Engineering and the Biomedical Imaging Institute, University of Manchester, United Kingdom

Anatomical connectivity mapping (ACM) is obtained by initiating tractography streamlines from all parenchymal voxels, and counting the number of streamlines passing through each voxel of the brain, thus highlighting WM structures strongly connected to the rest of the brain. DTI data from 10 subjects were normalised and averaged to compute the mean tensor, from which FA and ACM were obtained. Colour-coded maps of principal eigenvector, modulated by ACM are displayed. Several structures typically visible on colour-coded FA maps are visible also on ACM. Many other structures, however, can be seen more clearly and with greater resolution on the ACM images

14:30         3986.     Probabilistic Atlas of the Connections Between the Basal Ganglia and the Cortex

Linda Marrakchi-Kacem^1,2, Fabrice Poupon^1,2, Pauline Roca^1,2, Alan Tucholka^1,3, Christine Delmaire⁴, Eric Bardinet^4,5, Michael Sharman^4,5, Romain Valabregue^4,5, Arnaud Messe, ^2,6, Caroline Malherbe, ^2,6, Habib Benali, ^2,6, Alexandra Durr^7,8, Jean-François Mangin^1,2, Stephane Lehericy^4,5, Cyril Poupon^1,2

¹NeuroSpin, CEA, Gif-Sur-Yvette, France; ²IFR49, Gif-Sur-Yvette, France; ³Parietal, INRIA, Saclay, France; ⁴CENIR, Pitie-Salpetrière Hospital, France; ⁵INSERM U975, France; ⁶UMR-S 678 INSERM-UPMC, France; ⁷APHP, Pitie-Salpetrière Hospital, France; ⁸INSERM S679, France

The basal ganglia are topographically connected to cortical areas. These connections define motor, associative and limbic territories. These basal ganglia are therefore involved in motor as well as cognitive and behavioral functions. Dysfunction of basal ganglia territories leads to various neurological diseases that are specifically associated with each territory. In this abstract, we present the design of a surface probabilistic atlas of the connections between the basal ganglia and the interface between the white matter (WM) and the cortex. Such an atlas can be built on a population of healthy subjects as well as on a population of specific patients. Statistical tools can then be used to detect the regions with significant differences on the cortex that may correspond to underlying abnormalities of the striato-pallido-cortical connections. Such differences could yield new biomarkers of neurological pathologies.

15:00         3987.     Constant and Variable Features of White Matter Anatomy in the Human Brain: An in Vivo Diffusion Tractography Study

Michel Thiebaut de Schotten¹, Flavio Dell'acqua, Dominic ffytche², Matthew Allin³, Muriel Walshe³, Robin Murray⁴, Steve Williams², Declan Murphy¹, Marco Catani²

¹Brain Maturation, Institute of Psychiatry, London, United Kingdom; ²Centre for Neuroimaging Sciences, Institute of Psychiatry, London; ³Department of Psychiatry, Institute of Psychiatry, London; ⁴Department of Psychological Medecine, Institute of Psychiatry, London

Increasing knowledge of white matter organization has recently been derived from diffusion tensor tractography but access to this knowledge has often been limited to Diffusion Tensor Imaging (DTI) experts. Therefore a tractography atlas of the human brain pathways is timely for a better comprehension of brain function. However, this endeavour may be compromised by methodological limitations of the DTI technique and the high degree of inter-individual anatomical variability. Here we combine group effect maps with a spatial overlap approach to develop a 3D probabilistic atlas that provides comprehensive information about inter-subject variability and general morphology of the tract.

13:30         3988.     Anatomy the Fronto Parietal Pathways Correlates with the Symmetrical Processing of Visual Scenes

Michel Thiebaut de Schotten¹, Flavio Dell'Acqua¹, Stephanie Forkel¹, Marco Catani²

¹Brain Maturation, Institute of Psychiatry, London, United Kingdom; ²Centre for Neuroimaging Sciences, Institute of Psychiatry, United Kingdom

The fronto-parietal network has been reported as involved in a large panel of function including spatial processing. In the monkey brain, Petrides & Pandya used the term superior longitudinal fasciculus (SLF) to indicate the fronto-parietal connections and identified three separate branches. In this study we have used advanced diffusion imaging to dissect the three branches of the SLF in 14 human living brains, measure the pattern of lateralization of its components and correlate these patterns with the spatial processing performance assessed with the line bisection test.

14:00         3989.     Quantification of Perfusion Contributions Using DWI Using Low B-Values

Jonathan Chia¹, Zhiyue J. Wang², Dah-Juu Wang³, Nancy K. Rollins²

¹Philips Healthcare, Cleveland, OH, United States; ²Radiology, Children's Medical Center of Dallas, Dallas, TX, United States; ³The Children's Hospital of Philadelphia

Diffusion weighted imaging is originally sensitive to all types of motions of the spins, including both diffusion and perfusion. Simultaneous perfusion measurement may be still possible by inclusion of sampling with low b-values. DWI was performed with low and high b-values in order to quantify and characterize perfusion contributions using DWI at 1.5T and 3T.

14:30         3990.     Multi-Center Reliability of Diffusion Tensor Imaging

Vincent Alfonso Magnotta¹, Greg Bonett², Bradley Bolster³, Bryon Mueller⁴, Kelvin Lim⁵, Susumu Mori⁶, Karl Helmer⁷, Jessica Turner⁸, Sara Reading⁹, Mark Lowe¹⁰, Elizabeth Aylward¹¹, Laura Flashman^1,2, Jane Paulsen^1,3

¹Radiology, The University of Iowa, Iowa City, IA, United States; ²Psychiatry, The University of Iowa, Iowa City, 52242, United States; ³Siemens Medical Solutions, Rochester, MN, United States; ⁴The University of Minnesota, Minneapolis, MN, United States; ⁵Psychiatry, The University of Minnesota, Minneapolis, MN, United States; ⁶Radiology, Johns Hopkins University, Baltimore, MD, United States; ⁷Radiology, Massachusetts General Hospital, Boston, MA, United States; ⁸Psychiatry and Human Behavior, University of California Irvine, Irvine, CA, United States; ⁹Psychiatry, Johns Hopkins University, Baltimore, MD, United States; ¹⁰Radiology, Cleveland Clinic Foundation, Cleveland, OH, United States; ¹¹Seattle Children's Research Institute, Seattle, WA, United States; ¹²Psychiatry, Dartmouth, Hanover, NH, United States; ¹³Psychiatry, The University of Iowa, Iowa City, IA, United States

A multi-center study of diffusion tensor imaging was conducted to evaluate the coefficient of variation for sequence, site, and vendor. Small variations of less than 1% were found within a site that increased to 3% across vendors.

15:00         3991.     Multi-Site Investigation of DTI Reproducibility

Karl Gerard Helmer¹, Ming-Chung Chou², Allen Song³, Jessica Turner⁴, Barjor Gimi⁵, Susumu Mori⁶

¹Radiology, Massachusetts General Hospital, Charlestown, MA, United States; ²Department of Computer Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan; ³Duke University, Durham, NC, United States; ⁴University of California, Irvine, Irvine, CA, United States; ⁵UT Southwestern Medical Center at Dallas, Dallas, TX, United States; ⁶Johns Hopkins University School of Medicine, Baltimore, MD, United States

The addition of diffusion tensor imaging to the protocol of multi-site studies has become more common in recent years.  However, few studies have been performed on the reproducibility of tensor metrics across site and scanner manufacturer.  We present data using scanners from Siemens, Philips, and GE and look at the behavior of the fractional anisotropy as decreasing amounts of data and/or diffusion-weighted directions are used in the tensor calculation.  The methods used in this study are also suitable for the site-reliability characterization before a multi-site study is begun or after upgrades during the study.

13:30         3992.     Voxel-Based DTI of Longitudinal Changes Post Pediatric TBI Compared with Age-Matched Developing Controls

Lian Xue¹, Khader M. Hasan, Larry A. Kramer, Linda Ewing-Cobbs

¹Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston, Houston, TX, United States

Quantitative diffusion tensor imaging (DTI) has been used to detect serial microstructure changes post moderate and severe TBI.  DTI metrics such as fractional anisotropy (FA), mean diffusivity (MD), axial and radial diffusivities, ƒÉ// and ƒÉ�Û revealed subtle differences of grey matter (GM) and white matter (WM) during recovery from TBI.  However, there is no systematic whole brain study on the longitudinal evolution of GM and WM diffusion abnormalities during recovery from pediatric TBI patients.  In this work, we perform a longitudinal study of 25 pediatric TBI patients who sustained moderate and severe TBI and 21 age-matched pediatric orthopedic comparison subjects.  DTI was acquired 3 months after injury for each participant and repeated at 24 months after injury for each participant to examine recovery in the TBI group in relation to normal neurodevelopment changes during childhood and adolescence.  Voxel based morphometry (VBM) [3] is adopted for an unbiased longitudinal data analysis and an optimal VBM procedure using the recently available DARTEL technique in SPM8 is developed to minimize misregistration.  The VBM results for FA, MD maps of GM and FA, ƒÉ// and ƒÉ�Û maps of WM reveal different longitudinal changes in TBI patient cortical and subcortical structures compared with normal neurodevelopment changes, which provide insight into the significant impact of TBI on GM and WM.

Diffusion:  Pulse Sequences

14:00         3993.     Reduced Field of View Diffusion Weighted Imaging of the Brain at 7T

Cornelius von Morze¹, Douglas A. Kelley², Suchandrima Banerjee², Timothy M. Shepherd¹, Duan Xu¹, Christopher P. Hess¹

¹Department of Radiology and Biomedical Imaging, UCSF, San Francisco, CA, United States; ²GE Healthcare, San Francisco, CA, United States

Ventral regions of the brain are an important research target in the early detection of Alzheimer’s disease, but standard single shot EPI diffusion weighted imaging of these areas at 7T is contaminated by severe imaging artifacts. To reduce these, we investigated a combination of reduced FOV acquisition, enabled by outer volume suppression with custom designed quadratic phase RF pulses, with existing parallel imaging and partial Fourier methods. The reduced FOV diffusion acquisition greatly reduced the level of artifacts in five human subjects (including four patients with early symptoms of dementia).

14:30         3994.     Diffusion Weighted Imaging at 7T with STEAM-EPI and GRAPPA

Bibek Dhital¹, Robert Turner¹

¹Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Saxony, Germany

Standard diffusion sequences require long time to play diffusion gradients, especially for high b-values. At 7T,this compromises higher intrinsic SNR with shorter T2  relaxation. We used STEAM sequence for slice localization and EPI with parallel imaging to acquire diffusion weighted images. While STEAM-EPI loses half the signal, it still benefits from a long T1 of the tissue to achieve high b-values: parallel imaging shortens EPI echo train leading to reduced distortions. STEAM-EPI is thus, the method of choice for 7 Tesla.

15:00         3995.     Improving Sensitivity in Low SNR Diffusion Imaging Using Optimal SNR Coil Combinations

Jennifer A. McNab^1,2, Jonathan A. Polimeni^1,2, Julien A. Cohen-Adad^1,2, Lawrence L. Wald^1,3

¹A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States; ²Harvard Medical School, Boston, MA, United States; ³Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

Sum-of-squares (SoS) is the standard method for combining multi-channel coil images. SoS implicitly assumes that the pixel intensity is a reasonable estimate of the coil sensitivity profile. While this may hold true for acquisitions with high SNR and ideal arrays, diffusion-weighted images often have low SNR. We demonstrate improved sensitivity to diffusion measures using coil sensitivity estimates from high SNR b = 0 images as well as a quick determination of the noise covariance between coil channels to improve the channel combination. This approach adds 20 s of scan time but can increase fractional anisotropy estimates, for example, by 30%.

15:30         3996.     Accelerated DWI Using Simultaneous Image Refocused EPI Optimized for Clinical Imaging

Vibhas Deshpande¹, Sudhir Ramanna^2,3, David Feinberg^2,3

¹Siemens Medical Solutions USA., Inc., San Francisco, CA, United States; ²Advanced MRI Technologies, Sebastopol, CA, United States; ³University of California, Berkeley, CA, United States

To reduce imaging times in clinical diffusion imaging, the simultaneous image refocusing (SIR) technique can be utilized to acquire multiple slices in a single readout, thereby shortening the total scan time.  With 2 simultaneously refocused echoes, an approximate acceleration factor of 1.5 can be achieved as compared to non-SIR imaging.  Results showed that the image quality using the SIR sequence was comparable to the conventional EPI, non-SIR sequence.  In conclusion, SIR with 2 simultaneous slices can reduce scan time in diffusion weighted imaging by a factor of 1.5 with a compromise in spatial distortions and a small penalty in SNR.

13:30         3997.     Diffusion Imaging with Prospective Motion Correction and Reacquisition

Thomas Benner¹, Andre J.W. van der Kouwe¹, A. Gregory Sorensen¹

¹Radiology, Athinoula A. Martinos Center, Charlestown, MA, United States

Subject motion is a major source of image artifacts in diffusion imaging, causing misalignment of images and erroneous values in the derived maps. A method is proposed that includes prospective motion correction as well as reacquisition of image data affected by motion. Result show that motion tracking is comparable to offline methods and that detection of images with artifacts works well. The corrected data is comparable to data acquired without subject motion at the cost of slightly increased scan time.

14:00         3998.     Efficient DTI Artifact Correction Via Spatial and Temporal Encoding

Zhikui Xiao¹, Hao Shen¹, Guang Cao¹, William Scott Hoge²

¹Applied Science Lab, GE Healthcare, Beijing, China; ²Radiology, Brigham and Women's Hospital, Boston, MA, United States

By adding an extra shifted b0 acquisition to the standard DTI sequence, we present a method to fuse spatial and temporal encoding to correct for both Nyquist ghosts and geometric distortion artifacts in DTI.

14:30         3999.     A Method for Gradient Calibration in Diffusion Weighted Imaging

Oleg Posnansky¹, Yuliya Kupriyanova², N. J. Shah^1,3

¹Medical Imaging Physics, Institute of Neuroscience and Medicine - 4 , Forschungzentrum Juelich, Juelich, Germany; ²Medical Imaging Physics, Institute of Neuroscience and Medicine - 4, Forschungzentrum Juelich, Juelich, Germany; ³Department of Neurology, Faculty of Medicine,RWTH Aachen University, Aachen, Germany

A calibration method for diffusion-weighted imaging using a homogeneous water phantom is proposed.  The key point of the method consists in finding optimised balancing times for different orientations of diffusion-encoding gradients followed by retrospective rescaling of the diffusion-weighted images. The correction protocol was applied to produce improved fractional anisotropy maps. The results demonstrate that the described scheme of systematic error reduction is a valid approach for quality control studies of gradient system performance for diffusion-weighted imaging.

15:00         4000.     Reduce Blurring Effects in PROPELLER QBI - not available

Ming-Chung Chou¹, Yen-Wei Cheng², Cheng-Wen Ko¹, Tzu-Chao Chuang³, Fu-Nien Wang⁴, Teng-Yi Huang⁵, Hsiao-Wen Chung²

¹Computer Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan; ²Electrical Engineering, National Taiwan University, Taipei, Taiwan; ³Electrical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan; ⁴Biomedical Engineering and Environmental Science, National Tsing Hua University, Hsinchu, Taiwan; ⁵Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan

Although PROPELLER QBI was demonstrated to reduce scan time and susceptibility distortions while resolving fiber crossings, the residual phase errors in blade DWIs will cause blurring effects in reconstructed image. The purpose of this study was to conduct distortion correction by using image registration in PROPELLER EPI reconstruction, so as to further reduce susceptibility distortions in PROPELLER QBI.

13:30         4001.     Using Absorption-Mode Images to Improve in Vivo DTI Quality

Tsang-Wei Tu^1,2, Matthew D. Budde³, James D. Quirk², Sheng-Kwei Song²

¹Mechanical, Aerospace and Structural Engineering, Washington University in St. Louis, Saint Louis, MO, United States; ²Radiology, Washington University in St. Louis, Saint Louis, MO, United States; ³Radiology and Imaging Science, National Institutes of Health Clinical Center, Bethesda, MD, United States

Diffusion-weighted multiple spin echo (DW-MSE) sequences have been introduced to improve DTI quality without increasing scan time by combining the images of multiple echoes. Since complex image combination can cause artifacts due to phase variations between echoes, magnitude images are often employed. But this results in a noise distribution change from Gaussian to Rician leading to a SNR decline and biased tensor estimation. Our results demonstrate that absorption-mode addition of multiple echoes obtained using the DW-MSE sequence improves SNR by nearly 50% compared to a conventional DW-SE sequence and also overcomes the problem of phase variations without Rician noise complications.

14:00         4002.     7T Diffusion Imaging of Rat by Using SNAILS and Its Application in Stroke Study

Jian Zhang^1,2, Joshua Chua³, Chunlei Liu⁴, Shangping Feng¹, Michael Moseley²

¹Department of Electrical Engineering, Stanford University, Stanford, CA, United States; ²Department of Radiology, Stanford University, Stanford, CA, United States; ³Department of Neurosurgery, Stanford University, Stanford, CA, United States; ⁴Brain Imaging and Analysis Center, Duke University Medical Center, Durham, NC, United States

Animal stroke studies with DWI are widely investigated to facilitate the development of stroke diagnosis. However, diffusion imaging on small animals at high fields is usually very challenging due to the resolution-SNR tradeoff and hardware imperfection. The widely used single shot EPI DWI technique is particularly vulnerable to these factors and tends to produce severe image artifacts. In this work, we demonstrate the implementation of the self-navigated interleaved spirals (SNAILS) technique on our 7T animal scanner. High quality DWI images can be acquired for stroke studies on rats. The preliminary diffusion tensor imaging (DTI) results are also presented.

14:30         4003.     Diffusion-Weighted Balanced SSFP (DW-BSSFP): A New Approach to Diffusion Tensor Imaging

Matthew M. Cheung^1,2, Jerry S. Cheung^1,2, Li Xiao^1,2, April M. Chow^1,2, Kannie W. Chan^1,2, Ed X. Wu^1,2

¹Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong, China; ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong, China

Although DW-EPI offers high acquisition speed, it generally suffers from low spatial resolution and geometric distortion. SSFP is a possible alternative to perform diffusion imaging with higher resolution and with no distortion artifacts that is inherent in EPI. In this study, we modified the balanced SSFP sequence by adding a pair of bipolar diffusion sensitizing gradients. The diffusion effect in bSSFP sequence with a pair of bipolar diffusion gradients was formulated and DW-bSSFP experiment was performed on in vivo rat brain at 7T.

15:00         4004.     Improvements on Single-Shot STEAM with Optimised Signal Shaping for Diffusion Weighted Imaging at High Fields

Rüdiger Stirnberg¹, Tony Stöcker¹, N. Jon Shah^1,2

¹Institute of Neuroscience and Medicine - 4, Medical Imaging Physics, Forschungszentrum Jülich GmbH, Jülich, Germany; ²Faculty of Medicine, Department of Neurology, RWTH Aachen University, Aachen, Germany

It was recently shown that a diffusion weighted Single-shot Stimulated Echo Acquisition Mode (DW ss-STEAM) pulse sequence is an alternative to the standard DW EPI at high fields. By designing dedicated variable flip angles (vFA) for accurate, advanced signal shaping without RF spoiling, more signal is utilised. A clear advantage is drawn from parallel imaging due to less phase encoding lines. The results are: EPI-comparable SNR and acquisition time without geometrical distortions at high fields. A basis is now established to potentially incorporate all transverse coherences without interferences (current investigations) promising a further general SNR multiplication of two.

13:30         4005.     Evidence for Microscopic Diffusion Anisotropy in Spinal Cord Tissue Observed with DWV Imaging on a Whole-Body MR System

Marco Lawrenz¹, Martin Koch¹, Jürgen Finsterbusch¹

¹Department of Systems Neuroscience, University Medical Center, Hamburg-Eppendorf, Hamburg, Germany

Double-wave-vector diffusion-weighted imaging is able to detect microscopic diffusion anisotropy in macroscopically isotropic samples. So far, corresponding experiments were performed on NMR systems with high performance gradient coils (>=300mT/m). Here, experiments are presented that provide evidence for the observation of the anisotropy effect on a standard whole-body MR system.

14:00         4006.     Numerical Simulations of Double-Wave-Vector Diffusion-Weighting Experiments with Multiple Concatenations at Short Mixing Times

Jürgen Finsterbusch^1,2

¹Department of Systems Neuroscience , University Medical Center Hamburg-Eppendorf, Hamburg, Germany; ²Neuroimage Nord, University Medical Centers Hamburg-Kiel-Lübeck, Hamburg-Kiel-Lübeck, Germany

Double-wave-vector diffusion-weighting experiments where two diffusion weighting periods are applied successively in a single acquisition are a promising tool to investigate tissue microstructure, e.g. cell or compartment sizes. However, for the long gradient pulse durations required on whole-body MR systems the underlying signal modulation with the angle between the two wave vectors may be small which hampers the detectability of the effect. Here, it is shown that multiple concatenations of the two diffusion weightings in a single experiment can yield considerably higher signal modulations than expected theoretically because shorter gradient pulses are sufficient to achieve the desired diffusion weighting.

14:30         4007.     Multiple Echo Multi Shot (MEMS) Diffusion Sequence

Sergio Uribe^1,2, César Galindo³, Cristian Tejos, ^2,4, Pablo Irarrazaval, ^2,4, Steren Chabert³

¹Radiology Department, Pontificia Universidad Catolica de Chile, Santiago, Chile; ²Biomedical Imaging Center, Pontificia Universidad Catolica de Chile, Santiago, Chile; ³Biomedical Engineering Department, Universidad de Valparaiso, Valparaiso, Chile; ⁴Electrical Engineering Department, Pontificia Universidad Catolica de Chile, Santiago, Chile

T2 and diffusion measurements are usually acquire in different scans. In this work we propose a multi echo multi shot diffusion sequence that allows us obtaining T2 and mean diffusivity from a single scan. The multi shot approach enable short echo times for both echoes. This characteristic makes this sequence suitable to be applied in tissues with short T2. Result of in vivo experiments show an excellent correlation of T2 and mean diffusivity of the muscle compare to standard scans.

15:00         4008.     Extension of the Double Wave Vector Experiments at Long Mixing Times to Multiple Concatenations

Marco Lawrenz¹, Jürgen Finsterbusch¹

¹Department of Systems Neuroscience, University Medical Center, Hamburg-Eppendorf, Hamburg, Germany

An extension of the tensor approach to the double wave-vector experiment for multiple concatenations is presented aiming at the examination of microscopic anisotropy in tissue for fully restricted diffusion. A detailed analysis of the generalized tensor expression to the fourth order does not only hold for the characterization of arbitrary pores in an idealized environment but can still derive a microscopic anisotropy measure on the pore size level with sufficient accuracy for timing parameters compatible to whole-body MR systems. Monte Carlo simulations confirm the theoretical considerations.

Tractography

14:00         4009.     Fast Normalization of Probabilistic Tractography

Stephen Edward Jones^1,2, Kenneth Sakaie

¹Neuroradiology, Cleveland Clinic, Cleveland, OH, United States

Numerical computation of track density using probabalistic DWI can be inefficient, particularly for distant points. We present a method that uses a partial differential equation approach (Laplace's equation) to solve the special isotropic case of probablistic tracking. This provides a rapid solution for any two points within the brain, with arbitrary accuracy. This solution can be coupled with anisotropic probablistic tracking to obtain scalar measures of connectivity.

14:30         4010.     A Minimal Model, Data-Driven Approach to Tractography

Angela Downing¹, Daniel Rueckert², A David Edwards, ^1,3, Jo V. Hajnal¹

¹Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, United Kingdom; ²Visual Information Processing Group, Department of Computing, Imperial College London, London, United Kingdom; ³Department of Paediatrics, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, United Kingdom

We present a minimal model approach to tractography using the diffusion-weighted MRI measurements to represent samples from a diffusivity profile. Using phantom data we show that it is possible to accurately reconstruct the fibre structure between regions of interest by simulating the diffusion process that gives rise to the data.

15:00         4011.     A Principal Eigenvector Based Segmental Approach for Reproducible White Matter Quantitative Tractography

Shruti Agarwal¹, Richa Trivedi², Rakesh Kumar Gupta², Ram Kishore Singh Rathore¹

¹Department of Mathematics & Statistics, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh, India; ²Department of Radiodiagnosis, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India

Most common methods of fiber tracking rely on a knowledge based selection of ROIs on appropriate slice and then generating the fibers from there followed by cleaning and augmenting the bundle obtained. For a part of source and destination ROIs the procedure is similar. However, in practice the selection of the right ROIs and the subsequent additions and deletions are normally quite time consuming in practice and involves a considerable amount of trial and error. In this presentation we propose a principal eigenvector (e1) field segmentation using which the selection of ROIs becomes less time consuming.

15:30         4012.     A New Mahalanobis Distance Measure for Clustering of Fiber Tracts

Cheng Guan Koay¹, Carlo Pierpaoli¹, Peter J. Basser¹

¹NIH, Bethesda, MD, United States

In this work, we present a simple and novel generalization of Mahalanobis distance measure for the dyadics of the eigenvector for the purposes of clustering fiber tracts and fiber orientation. This approach is built upon a series of works by Koay et al. on the diffusion tensor estimation and the error propagation framework. The proposed Mahalanobis distance measure for the dyadics is the ideal measure for clustering of fiber tracts as it does not depend on ad hoc combinatorial optimization that is typical in the eigenvector-clustering techniques, which is due to the antipodal symmetry of the eigenvector.

13:30         4013.     A Multi-Structural Fiber Crossing Anisotropic Diffusion Phantom for HARDI Reconstruction Techniques Validation

Danilo Scelfo^1,2, Laura Biagi¹, Lucia Billeci^1,3, Michela Tosetti¹

¹MR Laboratory, Stella Maris Scientific Institute, Pisa, Italy; ²Department of Physics, University of Pisa, Pisa, Italy; ³Inter-departmental Research Center “E. Piaggio”, University of Pisa, Pisa, Italy

There is significant interest in evaluating the performance and reliability of white matter fiber tractography algorithms. DTI-based fiber tracking gives insights into the complex architecture of the brain. However, it is well known that it presents a number of limitations, especially in presence of fiber crossing, The validation of fiber reconstruction by these different approaches remains challenging and requires suitable test phantoms. An experimental model with different fiber crossing configurations has been projected and realized (PIVOH, Phantom with Intra-Voxel Orientation Heterogeneity), in order to simulate the structural complexity of the white matter, in correspondence of fiber intersection

14:00         4014.     A Novel Average Curves Tractography Technique - Validation Using a Physical Phantom

Nagulan Ratnarajah¹, Andy Simmons², Ali Hojjat¹

¹Medical Image Computing, University of Kent, Canterbury, United Kingdom; ²Institute of Psychiatry, Kings College London, United Kingdom

Probabilistic tractography algorithms differ from deterministic algorithms in that they take into account the uncertainty in fibre orientation. However, visualization of deterministic streamline trajectories is similar to the expected white matter fibre tracts, whereas the output of probabilistic methods may be harder to interpret and connectivity maps from probabilistic methods can leak into unexpected regions of white matter. In this study, we present a deterministic version of probabilistic tractography, which results in a single well defined trajectory for every major connection from a seed point using an average-curves approach. We evaluated the method on a physical-phantom and compared the results with the ground-truth.

14:30         4015.     How Many Streamlines Should I Use?

Matthew George Liptrot¹, Tim Bjørn Dyrby¹

¹Danish Research Centre for Magnetic Resonance (DRCMR), Copenhagen University Hospital, Hvidovre, Copenhagen, Denmark

In probabilistic streamline tractography, the choice of the number of streamlines to employ is the source of much confusion as no feasible analytical solution exists, and ensuring “sufficient” sampling is therefore problematic. Herein we describe an investigation into the influence that the number of streamlines imposes upon free-tracking, compare the parameter’s effect within Anatomical Connectivity Map generation and show how, via use of the ICE-T Framework (a recent technique to iterate conventional tractography routines), as few as 10 streamlines per voxel can be sufficient to overcome the omnipresent problem of path length dependency.

15:00         4016.     Application of Rotational Tensor Interpolation to Tractography

Marta Morgado Correia^1,2, Guy B. Williams²

¹MRC Cognition and Brain Sciences Unit, Cambridge, Cambridgeshire, United Kingdom; ²Wolfson Brain Imaging Centre, Cambridge, Cambridgeshire, United Kingdom

Diffusion MRI was the first imaging modality to allow the visualization of white matter fibre paths in vivo, and non-invasively. Tensor interpolation methods have often been used to improve the reproducibility and reliability of tractography results.

In this abstract we will introduce a new method for 3D tensor interpolation based on work by Batchelor and colleagues, and use simulated data to compare its performance to well established methodologies.

13:30         4017.     Identification of Corresponding Tracks in Diffusion MRI Tractographies

Eleftherios Garyfallidis^1,2, Matthew Brett³, Vassilis Tsiaras⁴, George Vogiatzis⁵, Ian Nimmo-Smith¹

¹MRC Cognition and Brain Sciences Unit, Cambridge, United Kingdom; ²University of Cambridge, Cambridge, United Kingdom; ³University of California, Berkeley, United States; ⁴Department of Computer Science, University of Crete, Greece; ⁵Computer Vision Group, Toshiba Research Europe, Cambridge, United Kingdom

Identifying manually corresponding tracks in different brain tractogaphies is a very complicated task, typically requiring lots of expertise, and lots of time. Moreover different local diffusion models and different tractography algorithms generate tractographies with wide differences in numbers of tracks and in shape characteristics. We address these problems by introducing an automatic method for detecting corresponding tracks in different dMRI (diffusion weighted MRI) datasets.

14:00         4018.     Automatic Tractography Segmentation by Morphological Continuity Clustering

Fang-Cheng Yeh¹, Wen-Yih Isaac Tseng²

¹Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States; ²Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan

We present a tractography segmentation algorithm called morphological continuity clustering (MCC), which is a fully automatic, unguided method that clusters fiber tracts without predefining the cluster number. This algorithm is based on the concept that the fibers of the same cluster share the morphological continuity, a feature used to determine whether two tracts should be grouped. The performance was evaluated on tractography with a total of 100,000 fibers tracts generated by streamline tracking method on generalized q-space imaging (GQI). The results showed that MCC is able to generate several clusters that correspond to well-known fiber tracts. Further study is needed to improve the accuracy and robustness of the proposed method.

14:30         4019.     False Positive Detection Using Filtered Tractography

Yogesh Rathi^1,2, James Malcolm, ²³, Sylvain Bouix¹, C-F Westin⁴, Martha E. Shenton^1,5

¹Psychiatry, Harvard Medical School, Boston, MA, United States; ²Georgia Institute of Technology, Atlanta, GA, United States; ³Brigham and Women's Hospital, United States; ⁴Radiology, Harvard Medical School, Boston, MA, United States; ⁵VA Clinical Neuroscience Division, Boston, MA, United States

Existing methods perform model estimation independently at each voxel and tractography is performed in the next step. We use a nonlinear Kalman filter for simultaneous model estimation and tractography. The method not only provides an estimate of the model parameters, but also a confidence in the estimation in terms of the covariance matrix. We utilize measures derived from this covariance matrix to detect false positives in the tracts generated.

15:00         4020.     Systematic Assessment of Effects of Noise and Resolution on Metrics of DTI Tractography

Virendra Radheshyam Mishra^1,2, Xin Fan², Hao Huang^3,4

¹Biomedical Engineering, The University of Texas at Arlington , Arlington, TX, United States; ²Advanced Imaging Research Center, The University of Texas  Southwestern Medical Center , Dallas, TX, United States; ³Advanced Imaging Research Center, The University of Texas Southwestern Medical Center , Dallas, TX, United States; ⁴Department of Radiology, The University of Texas Southwestern Medical Center , Dallas, TX, United States

Fiber volume and fiber count are two important metrics derived from DTI tractography. However, no systematic description of the relationship between these two measures and noise or resolution has been reported so far. In this study, we measured fiber count and fiber volume of left cingulum with DTI datasets of different SNR and resolution. Our results indicate that resolution plays a more important role on both measures than SNR. With a normal range of SNR, both measures are almost constant for a normal resolution. Compared to fiber count, fiber volume is a more stable measure.

13:30         4021.     SWI-Informed Diffusion Tensor Tractography

Michiel Kleinnijenhuis^1,2, Markus Barth^1,3, Daniel C. Alexander⁴, Anne-Marie van Cappellen van Walsum^2,5, David Gordon Norris^1,3

¹Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, Netherlands; ²Department of Anatomy, University Medical Centre St. Radboud, Nijmegen, Netherlands; ³Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany; ⁴Centre for Medical Image Computing, Department of Computer Science, University College London, London, United Kingdom; ⁵MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, Netherlands

Diffusion tensor tractography suffers from limited spatial resolution in the reconstruction of white matter structure. Susceptibility weighted images (SWI) also shows white matter structure, but can be acquired at a much higher resolution. A method is proposed to inform the tractography algorithm with gradient information (structure tensor) of the SWI intensity. Tracking was informed by SWI by projecting the DT tracking direction onto the plane orthogonal to the first eigenvector of the structure tensor. Main pathways were largely similar for DT and SWI-informed tractography, but tracts also showed marked differences between branching patterns and tract paths.

14:00         4022.     3D Tracking of Magnetic Pathways in White Matter Based on Magnetic Susceptibility Anisotropy

Chunlei Liu^1,2, Yi Jiang³, G. Allan Johnson³

¹Brain Imaging and Analysis Center, Duke University, Durham, NC, United States; ²Radiology, Duke University, Durham, NC, United States; ³Center for In Vivo Microscopy, Duke University, Durham, NC, United States

We propose a method for tracking a magnetic network existing in the white matter. The proposed method utilizes a previously unexplored magnetic property of white matter fibers. We found that the magnetic moment of white matter varies significantly when measured at different brain orientations with respect to the external field. This orientation dependence can be modeled by an apparent susceptibly tensor. Decomposing this tensor into its eigensystem revealed a spatially coherent network. Following the orientation of the major eigenvector, we were able to map distinctive magnetic pathways in 3D. The relationship between the magnetic network and fiber pathways is discussed.

14:30         4023.     BootGraph: Probabilistic Fiber Tracking Using Bootstrap Algorithm and Graph Theory

Robert Stefan Vorburger¹, Carolin Reischauer¹, Peter Boesiger¹

¹Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Bootstrap algorithms and graph theory are sophisticated methods in diffusion tensor imaging to obtain probabilistic connectivity maps in the human brain. In the present work the two methods are combined by weighting the graph edges with the statistics derived from the bootstrap approach. Hence, the resulting connectivity maps reflect not only directional probabilities but also the uncertainty in the measured data. Thereby, the time consuming bootstrap calculations have to be performed only once and can be used for different settings of tracking parameters, such as the FA threshold or curvature restriction.

15:00         4024.     Dual Tensor Tracking in Low Angular Resolution Diffusion Weighted MRI

Matthan W.A. Caan^1,2, M. M. van der Graaff¹, S. D. Olabarriaga¹, C. A. Grimbergen¹, L. J. van Vliet², F. M. Vos^1,2

¹Radiology, Academic Medical Center, Amsterdam, North-Holland, Netherlands; ²Imaging Science and Technology, Delft University of Technology, Delft, Netherlands

In Diffusion Weighted MRI, the diffusion weighting should be high enough to facilitate fiber tracking through crossings. We propose to estimate a dual tensor model on an entire cohort with low diffusion weighting and a limited number of gradient directions. Diffusion attenuation profiles of multiple subjects are regarded as realizations of a single underlying fiber distribution. Non-rigid coregistration ensures spatial correspondence. Increased angular resolution is ensured by random subject positioning in the scanner, as well as by anatomical heterogeneity. In our dual tensor atlas, we tracked fibers which proceeded contralaterally through the decussation of the superior cerebellar peduncle.

HARDI & Diffusion Modeling

14:00         4025.     Boosting the Angular Resolution of Q-Space Imaging Methods by Diffusion ODF Deconvolution

Fang-Cheng Yeh¹, Van Jay Wedeen², Wen-Yih Isaac Tseng³

¹Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States; ²MGH Martinos Center for Biomedical Imaging, Harvard Medical School, Charlestown, MA, United States; ³Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan

We present a deconvolution method that estimates fiber orientation distribution function (ODF) from diffusion ODF. Instead of applying deconvolution on spherical harmonic parameters, the proposed method performs deconvolution on the diffusion ODF directly, thereby extending its applicability to diffusion spectrum imaging (DSI) and generalized q-space imaging (GQI). To test the performance of the proposed method, we applied it to q-ball imaging (QBI), DSI, and GQI, with diffusion weighted images acquired by single-shell, grid, and two-shell sampling schemes, respectively. The result showed that the fiber ODFs obtained by the proposed method presented sharper contours in all tested q-space imaging method.

14:30         4026.     Classification of Non-Gaussian Diffusion Profiles for HARDI Data Simplification

Vesna Prškovska¹, Anna Vilanova¹, Cyril Poupon², Bart ter Haar Romeny¹, Maxime Descoteaux³

¹Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands; ²NeuroSpin, CEA Saclay, Gif-sur-Yvette, France; ³Computer Science, Université de Sherbrooke, Québec, Canada

This work presents a HARDI study of the classification power of different anisotropy measures. This classification aims towards separating the data into three compartments:  Isotropic, Gaussian and Non-Gaussian. Afterwards the data can be simplified in the first two compartments by simpler diffusion models.  To quantify the classification power of the measures, ex-vivo phantom data is used, and the findings are qualitatively illustrated on real data under different b-values and gradient sampling schemes. The benefits from the data simplification are clinically attractive due to the possibility of significantly decreasing the post-processing time of the HARDI models and faster, more intuitive visualization.

15:00         4027.     Effect of Diffusion Time on Diffusion Kurtosis in Neural Tissues

Edward S. Hui^1,2, Steve H. Fung^2,3, Ed X. Wu^1,4

¹Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong, Hong Kong; ²Department of Radiology Research, The Methodist Hospital Research Institute, Houston, TX, United States; ³Department of Radiology, Weill Medical College of Cornell University, New York, United States; ⁴Department of Electrical & Electronic Engineering, The University of Hong Kong, Hong Kong, Hong Kong

As diffusion-weighted (DW) signal attenuation not only depends on diffusion gradient strength but also the time separation between the 2 diffusion gradients (Δ), it is important to examine the effect of Δ on the kurtosis of the water displacement profile which could be estimated by a recently proposed robust and efficient technique known as diffusion kurtosis imaging (DKI). It quantifies the kurtosis of the water diffusion profile, by acquiring DW signal at multiple b-values by varying the diffusion gradient strength at fixed Δ. The effect of Δ on kurtosis has been studies in vivo for the first time to assess its potential in teasing biological information underlying neural microstructures.

15:30         4028.     Diffusional Kurtosis Imaging (DKI) in the Normal Cervical Spinal Cord at 3 T : Baseline Values and Diffusion Metric Correlations

Eric Edward Sigmund¹, Maxim Bester^1,2, Ali Tabesh¹, Matilde Inglese¹, Joseph A. Helpern¹

¹Radiology, New York University Langone Medical Center, New York, NY, United States; ²Neuroradiology, University Hamburg-Eppendorf, Hamburg, Germany

The microstructural sensitivity of diffusion-weighted imaging is a powerful diagnostic in degenerative spinal cord (SC) disorders, and its specificity to different pathologies can be amplified with advanced protocols that exceed the Gaussian diffusion approximation.  To that end, this study presents diffusional kurtosis imaging in the cervical spinal cord of healthy control subjects at 3 T.  A set of diffusion tensor (MD, FA, D_axial,D_radial) and kurtosis tensor (MK, K_axial,K_radial)  metrics are derived.  Diffusion and kurtosis metrics are observed to inversely correlate (e.g. low radial diffusion with high radial kurtosis), which is discussed in the context of SC microstructure.

13:30         4029.     A Theoretical Framework to Model Diffusion MRI Signals Taking Into Account Cell Membranes

Jing-Rebecca Li¹, Cyril Poupon², Denis Le Bihan²

¹Institut national de recherche en informatique et automatique (INRIA), Rocquencourt, France; ²NeuroSpin, CEA, Saclay, France

We model diffusion in biological tissue and simulate MRI signal attenuation by solving a partial differential equation model with several diffusion compartments, coupled with appropriate interface and boundary conditions. We use a method based on heat layer potentials derived from the relevant Green's function. This method is an alternative to Monte-Carlo or finite difference based simulation methods. An advantage is that much larger time steps can be used in simulation, while preserving accuracy and stability of the numerical method.

14:00         4030.     In Vivo DTI Parameter Choice Using Monte-Carlo Diffusion Simulations in a Model of Brain White Matter

Franck Mauconduit¹, Hana Lahrech¹

¹Functional and Metabolic Neuroimaging - Team 5, Grenoble Institute of Neuroscience, La Tronche, France

In this study, simulated diffusion-weighted signal in a model of white matter was developed in order to study the relationship between diffusion time (tdif) and ADC values. In vivo water diffusion experiments on the corpus callosum of the rat brain were performed and compared to the simulated data. For in vivo experiments and according to our simulated results, maximal and minimal ADC values were found independent on tdif. Therefore in vivo measurements would rather be acquired with a short tdif than with a larger one, resulting in a higher Signal to Noise Ratio.

14:30         4031.     Monte-Carlo Simulation Software Dedicated to Diffusion Weighted MR Experiments in Neural Media

Chun-Hung Yeh^1,2, Denis Le Bihan¹, Jing-Rebecca Li¹, Jean-Francois Mangin¹, Ching-Po Lin², Cyril Poupon¹

¹NeuroSpin, I2BM, CEA, Gif-sur-Yvette, France; ²National Yang-Ming University, Taipei, Taiwan

We develop a novel Monte-Carlo simulation tool dedicated to DW MR experiments by combining a Brownian dynamics simulator capable of simulating water diffusion in arbitrary geometries reproduced using meshes with a DW signal integrator emulating various MR pulse sequences. Complicated configurations mimicking neural tissue components (e.g. neurons) can be emulated, as well as tissue features (e.g. membrane permeability) and basic diffusion mechanisms in different compartments. This framework allows to bridge the gap between elementary processes and the resulting DW signal, providing a better understanding of the features observed in DW-MRI (e.g. ADC), and to optimize acquisition schemes for different applications.

15:00         4032.     Comparison of Spin Echo and Steady-State Free Precession Sequences for Diffusion Tractography of Whole, Ex-Vivo Human Brains

Karla L. Miller¹, Gwenaelle Douaud¹, Saad Jbabdi¹, Timothy EJ Behrens¹, Jennifer A. McNab²

¹FMRIB Centre, Oxford University, Oxford, Oxon, United Kingdom; ²AA Martinos Center, Massachusetts General Hospital, Charlestown, MA, United States

Despite its popularity, there is relatively little data validating diffusion tensor imaging and tractography against gold-standard histology or dissection methods. Diffusion imaging of whole, ex-vivo human brains could provide this link by allowing comparison in the same tissue. We present results obtained using diffusion-weighted spin echo (DW-SE) and steady-state free precession sequences (DW-SSFP), each with 6 hours scan time on a clinical scanner. Both methods are able to track the corticospinal tract and corpus callosum. However, tractography of DW-SSFP data produces better quality tracking due to the lower uncertainty on principal tract direction.

13:30         4033.     Effect of Diffusion Time and B-Value on Quantitative DTI

Edward S. Hui^1,2, Steve H. Fung^2,3, Ed X. Wu^1,4

¹Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong, Hong Kong; ²Department of Radiology Research, The Methodist Hospital Research Institute, Houston, TX, United States; ³Department of Radiology, Weill Medical College of Cornell University, New York, United States; ⁴Department of Electrical & Electronic Engineering, The University of Hong Kong, Hong Kong, Hong Kong

Diffusion-weighted (DW) signal attenuation depends on not only the diffusion gradient strength but also the separation between the two diffusion gradients (i.e., diffusion time Δ). In this study, the effect of Δ and diffusion weighting factor b-value was examined and documented for conventional DTI by acquiring DW signals with various b-values at different Δ from normal adult rat brains in vivo.

14:00         4034.     Combined T1- And DTI Weighted Contrast for High Resolution Human Brain Mapping Using 3D MPRAGE

marzieh Nezamzadeh^1,2, Gerald B. Matson, ²³, Yu Zhang^1,2, Michael W. Weiner^1,2, Norbert Schuff^1,2

¹radiology, University of California San Francisco, san francisco, CA, United States; ²Center for Imaging of Neurodegenerative Diseases, CIND, VA medical center, San Francisco, san francisco, CA, United States; ³Pharmaceutical Chemistry, University of California San Francisco, san francisco, CA, United States

Previously, magnetization-prepared rapid gradient-echo (MPRAGE) has been combined with diffusion encoding to achieve diffusion tensor imaging (DTI).  However, an incorporation of DTI contrast in 3D-MPRAGE has not been shown before on human brain data. Furthermore, a combination of T1 and DTI weighted contrast should benefit assessment of gray/white matter boundaries, which has important implications for accurately imaging brain atrophy. The overall goal of this study was to develop multiple contrast high resolution MRI. Specifically, we show the incorporation of DTI contrast, e.g. fractional anisotropy (FA) and mean diffusivity (MD), into T1-weighted 3D-MPRAGE using simulations and experimental results from human brain at 4T.

14:30         4035.     Effects of B-Matrix Correction on Fiber Tractography in High Resolution DTI with Short-Axis Propeller EPI

Murat Aksoy¹, Samantha Jane Holdsworth¹, Stefan Tor Skare^1,2, Roland Bammer¹

¹Department of Radiology, Stanford University, Stanford, CA, United States; ²Karolinska Institute, Stockholm, Sweden

Due to the prolonged acquisition time in DTI, the likelihood of patient motion increases. It is essential to correct for motion to assure the diagnostic quality and accuracy of tensor orientation in DTI. For interleaved sequences, such as Short-Axis Propeller-EPI, patient motion causes the b-matrix to vary between different parts of k-space. It was previously shown that correction of motion artifacts in this case requires non-linear methods. In this study, we investigated the effects of b-matrix correction on fiber tractography with high resolution DTI. Results showed that b-matrix correction is necessary to get accurate fiber tracts in moving subjects.

15:00         4036.     Sensitivity of Motion Estimation to the Anisotropic Diffusion of White Matter in Diffusion MRI

Kwan-Jin Jung¹

¹Brain Imaging Research Center, Univ. of Pittsburgh and Carnegie Mellon University, Pittsburgh, PA, United States

Motion correction is critical in diffusion weighted (DW) imaging, but the motion correction quality depends on the accurate motion estimation of the DW images. However, the motion estimation of the DW images can be sensitive to the anisotropic white matter. This has been confirmed using the DW images obtained from an anesthetized and immobilized monkey’s head and from a volunteer’s head. The error in the motion estimation was increased significantly at a higher b value such as b=2400 s/mm². It is required to develop a new method of motion estimation that is insensitive to the white matter anisotropy.

13:30         4037.     A Generalized Diffusivity for Tuning Diffusion-Weighted Imaging Contrast

Mariana Lazar¹, Jens H. Jensen¹, Joseph A. Helpern¹

¹Department of Radiology, New York University School of Medicine, New York, United States

In this abstract we introduce a new measure, the generalized diffusivity, to characterize diffusion in biological tissues. The generalized diffusivity include a tuning parameter,α , that allows differential weighting of diffusion paths on different length scales. For α=2, the generalized diffusivity reduces to the conventional mean diffusivity.

14:00         4038.     Dependence of Fractional Anisotropy on Diffusion Time: A Frequency-Domain Analysis Using Temporal Diffusion Spectroscopy

Junzhong Xu¹, Ha-Kyu Jeong¹, Mark D. Does¹, Adam W. Anderson¹, Li Min Chen¹, John C. Gore¹

¹Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States

The FA dependence on diffusion time was studied using temporal diffusion spectroscopy, which employs an oscillating gradient spin echo sequence and has the ability to probe much shorter diffusion times. A clear dependence of white matter factional anisotropy on effective diffusion time has been observed in a fixed monkey brain. The results were also predicted by computer simulations. The dependence observed in this study provides a means to probe diffusion restriction and hindrance at sub-cellular length scales, e.g. intracellular structures, and may provide insights into the microstructure of biological tissues and clarify the origins of anisotropy diffusion in white matter.

14:30         4039.     Improved, Real-Time Artifact Detection and Reacquisiton for Diffusion Tensor Imaging (DTI)

Yue Li^1,2, Steven M. Shea^2,3, Hangyi Jiang³, Christine H. Lorenz^2,3, Susumu Mori³

¹Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States; ²Center for Applied Medical Imaging, Siemens Corporate Research, Baltimore, MD, United States; ³Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, United States

Subpixel motion artifacts caused by pulsation often introduces severe artifacts in diffusion weighted images and incorrect tensor estimation. Previously fitting-based outlier rejection methods have been proposed to obtain robust tensor estimation. This presentation extended the past efforts from two aspects. First, a new non-fitting-based quality criterion was added, which outperforms the existing method when fitting becomes unstable due to multiple outliers. Second, we implemented this algorithm into Siemens Image Calculation Environment such that reacquisition of corrupted slices can occur inline. Preliminary test results showed improvements with our method and reacquisition of data in real-time reduced the presence of artifacts.

15:00         4040.     Combining Registration and Outlier Rejection in Preterm DTI Data

Drew Morris¹, Revital Nossin-Manor¹, Margot J. Taylor¹, John G. Sled^2,3

¹Diagnostic Imaging, Hospital for Sick Children, Toronto, Ontario, Canada; ²Physiology Experimental Medicine, Hospital for Sick Children, Toronto, Ontario, Canada; ³Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

When processing DTI data it is unclear as to whether outlier rejection should be done before or after correction steps which involve registration and resampling. Resampling outliers can corrupt adjacent data, while detecting outliers in uncorrected data can cause false outlier detection. We investigate this problem in processing pipelines for DTI in preterm neonates. We propose a method to tackle outlier rejection and registration based corrections simultaneously.

Diffusion Perfusion:  Animal Models

14:00         4041.     Hippocampal Neurogenesis Visualized by Diffusion Tensor Imaging

Chiao-Chi V. Chen¹, Kuan-Chi Mo¹, Chen Chang¹

¹Functional and Micro-Magnetic Resonance Imaging Center, Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan

In vivo assessment of neurogenesis may serve as an important indication of brain functionality during brain development or pathologies. The present study utilizes diffusion tensor imaging (DTI) to capture this process alive, corroborated by immunohistology.

14:30         4042.     Assessment of Myocardial Heterogeneity Using the Supertoroid-Based Representation of Dt-Mri

Choukri Mekkaoui^1,2, Marcel Jackowski³, Roberto Martuzzi¹, Donald Dione¹, Albert Sinusas¹

¹Yale University School of Medicine, New Haven, CT, United States; ²Harvard Medical School, Boston, MA, United States; ³University of São Paulo

Supertoroids are a novel DT-MRI representation that provides indices of diffusivity (toroidal volume:TV) and anisotropy (toroidal curvature:TC). The purpose of this study is to establish the normal myofiber structure of the left ventricle (LV) using toroid-based indices and compare to traditional diffusion indices in normal porcine hearts. These new indices showed that the LV macrostructure was heterogeneous for both diffusivity and anisotropy between segments (Septum, RV/LV junction, and Free Wall) and within levels (basal, mid-ventricular, and apical). TV and TC demonstrate that diffusivity and anisotropy measures are complimentary, which may enhance the understanding of LV macrostructure in the normal heart.

15:00         4043.     Correlation of in Vivo DWI Injury Patterns with Finite Element Analysis of Mouse Spinal Cord Injury

Tsang-Wei Tu^1,2, Philip V. Bayly¹, Sheng-Kwei Song²

¹Mechanical, Aerospace and Structural Engineering, Washington University in St. Louis, Saint Louis, MO, United States; ²Radiology, Washington University in St. Louis, Saint Louis, MO, United States

Knowledge of the biomechanical properties of the spinal cord is crucial to understanding the mechanisms and damage thresholds of spinal-cord-injury (SCI). Numerical analysis, such as Finite Element Analysis (FEA), relies on accurate knowledge of the in vivo material properties to model the stress and strain fields in the spinal cord during rapid impact. In the present study, we compare the extent of SCI, evaluated using in vivo DWI, to the predictions of FEA modeling, using published values of mechanical parameters obtained in vitro. Our results support the hypothesis that that SCI injury pattern correlated with stress-strain fields predicted by FEA.

15:30         4044.     Stability of Repeat Measures of CBF in Aged Tg2576 and Wild Type Mice via CASL

James A. Goodman¹, Zhiyong Xie²

¹BioImaging Center of Emphasis, Pfizer, Inc., Groton, CT, United States; ²BioImaging Center of Emphasis, Pfizer, Inc, Groton, CT, United States

Cerebral blood flow is a physiological parameter that varies within populations and is subject to significant physiological noise. In order to quantify the test/retest stability of CBF measurement via MR, arterial spin labeling was performed three times in three different imaging session on each of five aged App(+)Tg2576 mice (TG) and five age-matched controls (WT). The coefficient of variation of repeat measurements within each animal was about two times larger in the TG group than in the WT group. Since measurements from both groups were interspersed, it appears as though physiological noise was the dominant noise component in these measurements.

13:30         4045.     k-Means and Graph Cuts Clustering of Diffusion MRI in Rat STN

Ellen Brunenberg¹, Erik Pelgrim¹, Bart ter Haar Romeny¹, Bram Platel²

¹Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands; ²Biomedical Engineering, Maastricht University Medical Center, Maastricht, Netherlands

Deep Brain Stimulation of the STN for Parkinson’s alleviates motor symptoms, but often causes cognitive or emotional side effects. In this abstract, we present the results of different clustering algorithms in order to separate the rat STN motor and cognitive/emotional parts. We performed k-means and graph cuts clustering on spherical harmonics coefficients for each voxel in an atlas-based ROI around the STN. Graph cuts clustering results in a medial STN cluster, which might correspond to the cognitive/emotional part of the rat STN. Future research could focus on other HARDI distance measures and on fiber tracking projections as clustering input.

14:00         4046.     Effects of Hypercapnia on DTI Quantification

Abby Ying Ding^1,2, Ed X. Wu^1,2

¹Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China; ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China

The accuracy of DTI derived parameters can directly affect the interpretation of underlying biological microstructures. However, the diffusivity measurements are likely to be confounded by the presence of vasculature. Nevertheless, little is known about to what degree blood signal from vasculature affects the diffusion quantitation. In this study, we examined the effects of hypercapnia on DTI quantification indices in anesthetized rat brains. It was found statistically significant changes occurred in all parametric DTI maps indicating that hemodynamic alterations can potentially affect the DTI indices and detection of tissue microstructures. Therefore, cautions must be taken when interpreting DTI parameters in vivo.

14:30         4047.     Resolving of Crossing Pathways in the Optic Chiasm of Marmoset Monkey Using Diffusion Tractography with High Spatial and Angular Resolution - not available

Keigo Hikishima^1,2, Masayuki Yamada³, Kanehiro Fujiyoshi⁴, Suketaka Momoshima⁵, Kenji Kawai¹, Masaya Nakamura⁴, Norikazu Tamaoki¹, Hideyuki Okano²

¹Central Institute for Experimental Animals, Kasawaki, Kanagawa, Japan; ²Department of Physiology, Keio University; ³Fujita Health University; ⁴Department of Orthopaedic Surgery, Keio University; ⁵Department of Radiology, Keio University

The marmoset has a well-developed visual pathway; therefore, it has been used for studying the development of the optic chiasm. We performed high angular resolution diffusion imaging (HARDI) with high spatial resolution of the ex vivo optic chiasm in order to resolve the crossing pathways. We succeeded in visualizing the precise fiber structure in the optic chiasm with semidecussation, therefore ex vivo HARDI will be powerful tool for studying the neuroanatomic features of the optic chiasm.

15:00         4048.     The Structural Basis of Functional Improvement in Post-Infarct Rat Hearts with Stem Cell Treatment

Yong Chen^1,2, Jia Zhong^1,2, Walter C. Low³, Jianyi Zhang⁴, Xin Yu^1,2

¹Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States; ²Case Center for Imaging Research, Case Western Reserve University, Cleveland, OH, United States; ³Department of Neurosurgery, University of Minnesota; ⁴Division of Cardiology, University of Minnesota

In this study, we combined in vivo functional assessment with ex vivo characterization of myocardial structure to investigate the long-term effects of stem cell therapy on the structural and functional remodeling in post-infarct rat hearts. Our results suggest that stem cell treated hearts manifested preserved myocardial structure, which provided structural basis for improved cardiac function.

13:30         4049.     White Matter Microstructural Alterations Induced by Chronic Cocaine Self-Administration: A Diffusion Tensor Imaging Study in the Rat

Alessandro Gozzi¹, Michela Tessari¹, Federica Agosta¹, Lisa Dacome¹, Mauro Corsi¹, Angelo Bifone¹

¹Neuroscience CEDD, GlaxoSmithKline, Verona, Verona, Italy, Italy

Cocaine abuse is often modelled in experimental paradigms where rats are trained to self-administer the drug. However, the exact degree to which these models replicate the neurofunctional and microstructural alterations observed in neuroimaging studies of cocaine-addicts remains unknown. Here we used Diffusion Tensor Imaging to investigate white matter integrity in a rodent model of long-term, long-access self-administration of cocaine. We found substantial microstructural alterations in the frontal corpus callosum, a hallmark of reduced white matter integrity consistently observed in cocaine abusers. These findings strengthen the construct-validity of this self-administration model to investigate the neuroanatomical substrates involved in the transition from occasional drug use to chronic drug consumption.

14:00         4050.     Chimpanzees’ Primary Motor Cortex Asymmetry and Its Association with Handedness – a Combined T1- And Diffusion-Weighted Magnetic Resonance Imaging (MRI) Study

Longchuan Li¹, Todd M. Preuss², James K. Rilling³, William D. Hopkins⁴, Matthew F. Glasser⁵, Bhargav Kumar⁶, Roger Nana⁶, Xiaodong Zhang², Xiaoping Hu⁶

¹Biomedical Imaging Technology Center, School of Medicine, Georgia Institute of Technology/Emory University, Atlanta, GA, United States; ²Division of Neuroscience, Yerkes National Primate Research Center, Atlanta, GA, United States; ³Center for Behavioral Neuroscience, Emory University, Atlanta, GA, United States; ⁴Division of Psychobiology, Yerkes National Primate Research Center, Atlanta, GA, United States; ⁵Department of Anthropology, Emory University, Atlanta, GA, United States; ⁶Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, United States

Recent studies indicate that chimpanzees show a population-level bias for the use of the right hand for certain tasks. Here we studied the chimpanzees’ hemispheric asymmetry in the precentral corticospinal tracts (pCST) using diffusion magnetic resonance imaging and its association with handedness. The depth of the central sulcus was also measured and their relationship with handedness and the asymmetry of the pCST were studied. The results show that handedness has an effect on the asymmetry of the central sulcus depth, but not the asymmetry of the pCST fractional anisotropy (FA). It is likely that the asymmetries of central sulcus depth and that of corticospinal FA are largely functionally independent in chimpanzees and hand dominance is related more strongly to interhemispheric differences in cortical gray matter volume than to interhemispheric differences of the corticospinal tract white matter indexed by FA.

14:30         4051.     A Comparative Study of MRI Diffusion-Related Parameters for the Early Detection of Radiation-Induced Tissue Changes in a Rodent Tumour Model

Frank Peeters¹, Dennis Rommel¹, Jorge Abarca-Quinones¹, Vincent Gregoire², Thierry Duprez¹

¹Medical Imaging, Université Catholique de Louvain, Brussels, Belgium; ²Center for Molecular Imaging and Experimental Radiotherapy, Université Catholique de Louvain, Brussels, Belgium

The diagnostic accuracy of  diffusion MRI related parameters derived from different techniques should be empirically assessed. We have performed a comparative study for the assessment of early effects of radiation therapy in a rodent tumour model (rhabdomyosarcoma in rats). Parameters obtained from DTI (2-points ADC, mono- and bi-exponential fits) and q-space imaging (tensor analysis) were compared. Our study shows that diffusion coefficients were very sensitive to radiation-induced tissue changes. Q-space analysis yielded at least the most sensitive parameter: the excess kurtosis of the distribution. The mean value and anisotropy of the tensors detected different sub-areas within irradiated tissue.

15:00         4052.     The Power of the Linear, Planar, and Tubular Tensor in Experimental Stroke

Miia Pitkonen¹, Aysan Durukan², Eric Pedrono³, Ivan Marinkovic², Turgut Tatlisumak², Usama Abo-Ramadan⁴

¹Biomedicum Helsinki, Experimental MRI laboratory             , Helsinki, Finland; ²Department of Neurology, Helsinki University Central Hospital, Helsinki, Finland; ³Biomedicum Helsinki, Experimental MRI Laboratory, Helsinki, Finland; ⁴Biomedicum Helsinki, Experimental MRI Laboratory, Helsinki, Finland

Diffusion tensor imaging can approximates the linear, planar, and tubular tensor using CL, CP, and CS. We want to characterize the evolvement of these indices following brain ischemia. We followed the evolvement of these indices in 3 cortex, subcortex, and corpus callosum. Following brain ischemia, no such systematic approach over an extended period of time, with CL, CP, and CS, has not yet been reported. Wistar rats were subjected to focal cerebral ischemia by transient suture occlusion (n = 9). They were imaged in the hyperacute (2 and 3.5 hours), acute (1, 2, and 3 days), subacute (4 days, 1, and 2 week), and in the chronic phase (4, 6, and 8 weeks) after the MCAO. The MRI measurements were performed with a 4.7 T MR Scanner. Following acute ischemia, indices indicated damage in the neuronal cell bodies and in the chronic ischemic tissue possible recovery.

13:30         4053.     Imaging Experience-Dependent Changes in White Matter Microstructure in Rats

Jan Scholz¹, Cassandra Sampaio¹, Stephen Mchugh², David Bannerman², Alexandr Khrapichev³, Nicola Sibson³, Heidi Johansen-Berg¹

¹FMRIB Centre, Oxford, United Kingdom; ²Experimental Psychology, Oxford, United Kingdom; ³Gray Institute for Radiation Oncology & Biology, Oxford, United Kingdom

Structural brain plasticity in response to experience or learning can be found even in the adult mammal brain. Here we use diffusion MRI to determine the scope and location of white matter changes in rodents which learn the morris water maze task. Comparing MRI data to histology within the same animal will potentially yield a useful association between the two. This association can then be applied to human MRI data where histology or other information about neuro-cellular changes in unavailable.

14:00         4054.     DYT1 Dystonia of Mice and Men

Aziz M. Ulug¹, An Vo¹, Miklos Argyelan¹, Wynne K. Schiffer¹, Lauren Tanabe², William T. Dauer³, David Eidelberg¹

¹The Feinstein Institute for Medical Research, Manhasset, NY, United States; ²Columbia UNiversity, New York, United States; ³University of Michigan Medical School, Ann Arbor, MI, United States

Dystonia is a neurological disease characterized by sustained involuntary muscle contractions.  Eight DYT1 heterozygous mice and six littermate controls using invivo MRI, FDG microPET and exvivo MRDTI were studied.  We compared changes in mouse “genecopy” of DYT1 dystonia with their wild type littermate controls.  We found that DYT1 mice exhibit metabolic and FA abnormalities that resemble the DYT1 patients.  The correlation between striatum and cerebellum metabolic activity and the correlation between the metabolic activity and the FA abnormalities are also shown.

14:30         4055.     Co-Registration of DTI Tractography with Gd-Enhanced T1 Imaging in Evaluation of CED Studies in the Rhesus Macaque

Elizabeth Zakszewski^1,2, Nagesh Adluru¹, Marina Emborg, ²³, Andrew L. Alexander^1,2

¹Waisman Laboratory for Brain Imaging and Behavior, University of Wisconsin, Madison, WI, United States; ²Dept. of Medical Physics, University of Wisconsin, Madison, WI, United States; ³Wisconsin National Primate Research Center, University of Wisconsin, Madison, WI, United States

We use landmark-based registration methods to co-register diffusion tensor images with T1-Weighted images of the same animal taken during a Convection Enhanced Delivery (CED) study to the rhesus putamen.  We then use the area of Gd-enhanced infusate at various time points as seeds to perform white-matter tractography, with the intent of visually evaluating the accuracy of the infusion.

Arterial Spin Labeling:  Methods

14:00         4056.     Improved Quantification of Cerebral Blood Flow Change Using Phase Information of SWI, Corrected by Arterial Oxygen Saturation - not available

Yuri Zaitsu¹, Kohsuke Kudo², Rie Yazu¹, Kinya Ishizaka³, Noriyuki Fujima¹, Satoshi Terae¹, Makoto Sasaki², Hiroki Shirato¹

¹Hokkaido University  Graduate School of Medicine, Sapporo, Hokkaido, Japan; ²Advanced Medical Research Center, Iwate Medical University, Japan; ³Hokkaido University Hospital, Japan

The phase difference between vein and background tissue is able to lead oxygen saturation in vein and flow. We propose a new formula, in which arterial oxygen saturation is taken into account, to calculate venous flow change using phase information. The purpose of this study is to compare two formulas (previous studies and our proposal), in the measurements of venous flow change under the drug and physiological load, and to compare the results with cerebral blood flow change measured by arterial spin labeling (ASL) technique. The flow calculating from previous formula had no correlation with CBF changes using ASL, whereas, the flow calculating from present one had weak correlation. The flow formula corrected arterial oxygen saturation supposes to be more useful than previous formula without correction.

14:30         4057.     Imaging of Oxygen Extraction Fraction Using Velocity Selective Excitation with Arterial Nulling (VSEAN)

Jia Guo¹, Eric C. Wong²

¹Department of Bioengineering, University of California San Diego, La Jolla, CA, United States; ²Department of Radiology and Psychiatry, University of California San Diego, La Jolla, CA, United States

We introduced a new method to image oxygen extraction fraction noninvasively using velocity selective excitation with arterial nulling (VSEAN). Compared to the QUIXOTIC method, VSEAN has following advantages: 1) higher SNR due to more relaxed venous blood; 2) no subtraction gives higher time efficiency; 3) insensitive to physiological noise; 4) a T2 map is generated every TR from multi-echo acquisition. Sequence design details were discussed and results from a human subject were presented.

15:00         4058.     A Straightforward Approach for Measuring Blood Transit Time in Major Blood Vessels

Qin Qin^1,2, Peter C.M. van Zijl^1,2

¹Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States; ²F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

Knowledge of blood transit time in major blood vessels can provide important clinical information about vascular circulation. It can also facilitate the selection of labeling delay in ASL for quantification of CBF. Here a novel method of measuring blood transit time is proposed, which used slice-selective spin labeling followed by multiple delay time points with very short interval. Transit time estimation in different blood circulation segments was demonstrated.

15:30         4059.     STAR-TFE Sequence for Arterial Spin Labeling in Abdominal Organs at 3T

Jing Yuan¹, Heather Ting Ma^1,2, Yi-Xiang Wang¹, David K.W. Yeung¹, James F. Griffith¹

¹Department of Diagnostic Radiology and Organ Imaging, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong; ²Department of Electronic and Information Engineering, Harbin Institute of Technology Shenzhen Graduate SchoolGradu, Shenzhen, Guangdong, China

Arterial spin labeling (ASL) is having many applications outside the brain. In the abdomen, many problems arise with the traditional single shot EPI acquisition for ASL such as distortion, low spatial resolution, susceptibility artifact, Nyquist ghost, and chemical shift. A turbo field echo (TFE) acquisition with STAR labeling (STAR-TFE) was developed to overcome these problems and applied for abdominal ASL at 3T. Significant image quality improvement was achieved. STAR-TFE has comparable temporal resolution with HASTE and b-ssfp acquisition, but with lower SAR and no banding artifact. STAR-TFE should be promising for abdominal perfusion in spinal bone marrow and kidney.

13:30         4060.     MT Effect of Q2TIPS in Multiple Inversion Time ASL Acquisitions

Enrico De Vita^1,2, David L. Thomas^2,3, Matthias Günther^4,5, Xavier Golay^1,3

¹Lysholm Department of Neuroradiology, National Hospital for Neurology and Neurosurgery, London, United Kingdom; ²Medical Physics and Bioengineering, University College London, London, United Kingdom; ³Institute of Neurology, University College London, London, United Kingdom; ⁴Mediri GmbH, Heidelberg, Germany; ⁵Fraunhofer MEVIS-Institute for Medical Image Computing, Bremen, Germany

In arterial spin labelling (ASL) acquisitions, multiple post-labelling delays (TI) are often used to quantify cerebral blood flow (CBF) without the potential errors associated with assumptions on bolus arrival time. Q2TIPS saturation is often additionally used to precisely define the temporal width of the tagged bolus and facilitate CBF estimation. However the Q2TIPS pulse train modifies tissue and blood signal via magnetisation transfer effects. Here, we examine this undesired effect in multi-TI ASL with 3D-GRASE, in particular how it alters the effectiveness of background suppression of static tissue and therefore impacts on the SNR of the ASL measurement.

14:00         4061.     Aliasing, Off-Resonance Saturation, and Residual Signal Analysis for PCASL

Tejas Nair¹, Rolf Pohmann², Michael Gach¹

¹Research Imaging Facility, Nevada Cancer Institute, Las Vegas, NV, United States; ²MRT, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany

The aliasing, off-resonance saturation, and residual signal (control-label) characteristics of pulsed continuous arterial spin labeling (PCASL) were measured in a 2% agar phantom using various values of label and control RF (B1) and gradient (Gmax) amplitudes. Aliasing and off-resonance saturation for both the label and control increased with increasing B1 but decreased with increasing Gmax. The residual signal also decreased with increasing Gmax.

14:30         4062.     Correction of Partial Volume Effects in PASL Perfusion Measurements

Marco Pimentel¹, Pedro Vilela², Inês Sousa^3,4, Patricia Figueiredo³

¹Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Lisbon, Portugal; ²Imaging Department, Hospital da Luz, Lisbon, Portugal; ³Instituto Superior Técnico, Lisbon, Portugal; ⁴Healthcare Sector, Siemens, S.A., Portugal

We developed a simple model to correct for partial volume effects (PVE's) in ASL imaging and studied its performance in the estimation of grey matter (GM) and white matter (WM) perfusion, as well as in the application of ASL to brain activation measurements in fMRI, in a group of 15 healthy subjects at 3T. Our results reveal the importance of performing an accurate segmentation in order to achieve a good correction of PVE’s, which can strongly influence the measured GM to WM perfusion ratio and also the perfusion changes due to activation.

15:00         4063.     Effects of Slice Orientation and Parallel Acquisition on EPI-Based PASL Perfusion Imaging in Areas with Susceptibility Artifact

Shih Yu Cheng¹, Yuan Yu Hsu², Wan Chun Kuan³, Mei Yu Yeh¹, Kun Eng Lim², Ho Ling Liu^1,4

¹Medical imaging and Radiological Sciences, Chang Gung University, Taoyuan, Taiwan; ²Medical Imaging, Buddhist Tzu Chi General Hospital, Taipei, Taiwan; ³Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan; ⁴Division of Medical Imaging and Intervention, Chang Gung Memorial Hospital, Taoyuan, Taiwan

ASL MRI using gradient-echo EPI suffers from susceptibility artifact in areas near air/tissue interfaces.  Previous fMRI studies investigated the optimal slice tilt to reduce the signal dropout in those areas.  Besides, parallel imaging can help by having shorter echo trains which reduces intra-voxel dephasing.  This study focused on the orbitofrontal cortex region and evaluates the effects of slice angle combined with parallel imaging on ASL image quality.  The results indicated that using parallel imaging could reduce the signal dropout caused by dephasing effect of susceptibility related field gradient.  Parallel imaging is also preferable due to less subject to slice orientation.

13:30         4064.     Minimizing Acquisition Time for Quantification of Regional Cerebral Blood Flow (RCBF) and Arterial Transit Time (ATT) Using Pseudo-Continuous ASL at 3.0T

Yasuhiro Fujiwara¹, Hirohiko Kimura², Tsuyoshi Matsuda³, Tomokazu Ishida¹, Kyouji Higashimura¹

¹Radiological Center, University of Fukui Hospital, Fukui, Japan; ²Radiology, University of Fukui, Fukui, Japan; ³GE Healthcare Japan, Tokyo, Japan

The purpose of this study was to evaluate the effect of the number of post labeling delay times and averages to reproduce and minimize acquisition time for precise rCBF quantification. As result of this study, When performing pCASL at post label delay of 0.5, 1.0, 1.5s, reproducible perfusion images were obtained with sufficient SNR in the condition of 12 averages. Using 3 time points protocol, scanning time can be minimized as short as 5 minutes.

14:00         4065.     A Modified Version of Hrabe-Lewis Model to Account  Dispersion of Labeled Bolus in Arterial Spin Labeling

Onur Ozyurt¹, Alp Dincer², Cengizhan Ozturk¹

¹Bogazici University, Biomedical Engineering Institute, Istanbul, Turkey; ²Acibadem University, School of Medicine, Department of Radiology

We propose a modified version of Hrabe-Lewis model for pulsed arterial spin labeling (pASL) signal and discuss its parameter estimation in a simulation with a realistic noise data coming from in vivo ASL measurements

14:30         4066.     Accounting for Dispersion in Arterial Spin Labeling Using the Mass Transport Model: Validation Using the Arterial Input Function

Samira Kazan¹, Michael Chappell^1,2, Mathias Gunther³, Stephen Payne¹

¹Biomedical Engineering, University of Oxford, Oxford, Oxfordshire, United Kingdom; ²Centre for Functional MRI of the Brain, University of Oxford, Oxford, Oxfordshire, United Kingdom; ³Department of Neurology , University of Heidelberg, Heidelberg

Dispersion of labelled blood water is a known issue in the quantification of cerebral blood flow using arterial spin labelling. A mass transport model (MTM) of the dispersion of a bolus of labelled blood within an artery has been recently presented. Here the MTM is validated by examining ASL data containing arterial signal. It is found to fit the data with lower error than alternative models. It also captured the increasing dispersion of the bolus during transit along the arterial tree, as evidenced by estimates of path length and mean flow speed.

15:00         4067.     Separation of Intravascular Signal in Multi-Inversion Time Arterial Spin Labelling MRI

Michael A. Chappell¹, Bradley J. MacIntosh^1,2, Manus J. Donahue¹, Matthias Günther^3,4, Peter Jezzard¹, Mark W. Woolrich¹

¹FMRIB Centre, University of Oxford, Oxford, United Kingdom; ²Imaging Research, Sunnybrook Research Institute, Toronto, Canada; ³Department of Neurology, Universitätsklinikum Mannheim, University of Heidelberg, Mannheim, Germany; ⁴mediri GmbH, Heidelberg, Germany

An important artefact in ASL measurements arises from labelled water that is still intravascular (IV) at the time of imaging. One solution is the application of flow suppression. An alternative, for multi-TI ASL, is to include the IV component within the Kinetic model whilst ensuring that this component is only used where the data supports it. In this work the two alternatives were compared in both healthy subjects and patients with stenoses. The model fitting approach was found to be a viable alternative to flow suppression, making it suitable where flow suppression is not desirable or feasible.

13:30         4068.     Selective Arterial Spin Labeling After Extra-Intracranial Bypass Surgery

Simon Konstandin¹, Patrick Michael Heiler¹, Johann Scharf², Lothar Rudi Schad¹

¹Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany; ²Department of Neuroradiology, Heidelberg University, Mannheim, Germany

Perfusion originating from the summed supply of all brain feeding arteries is commonly assessed. In this study, a slice selective inversion was compared to a multidimensional RF pulse to label only the artery of interest. By tagging the bypass of a patient, perfusion signal only exists in the according hemisphere of the brain. The perfusion measured by these SASL methods is consistent with a standard angiography. Therefore, these presented MR techniques may in part replace the assessment of revascularization success by conventional angiography.

14:00         4069.     From Optimized Vessel Encoded PCASL (Opt-VEPCASL) to Randomly-Encoded VEPCASL (Re-VEPCASL)

Jia Guo¹, Eric C. Wong²

¹Department of Bioengineering, University of California San Diego, La Jolla, CA, United States; ²Department of Radiology and Psychiatry, University of California San Diego, La Jolla, CA, United States

While optimized Vessel Encoded Pseudo-Continuous ASL (opt-VEPCASL) provides higher SNR efficiency, randomly-encoded VEPCASL (re-VEPCASL) may provide other benefits such as: 1) no planning or angiogram is needed; and 2) it is potentially insensitive to resonance offsets. These advantages may benefit clinical users. In this abstract, the advantages of opt-VEPCASL and re-VEPCASL are discussed, and the efficiency of random encoding is examined by simulation.

14:30         4070.     Distribution of Cerebral Blood Flow in the Nucleus Caudatus, Nucleus Lentiformis and Thalamus: A Territorial Arterial Spin Labeling Mri Study

Jeroen Hendrikse¹, Esben Thade Peteresen², Soke Miang Chng², Xavier Golay³

¹Radiology, UMC Utrecht, Utrecht, Netherlands; ²National Neuroscience Institute, Singapore; ³University College London, United Kingdom

We investigate the effect of variations in the circle of Willis anatomy on the perfusion territory contributions to the deep brain structures.. Perfusion territory MRI could evaluate the deep brain structures in 119 of159 patients. In patients with a fetal type circle of Willis, there was a contribution from the ipsilateral ICA to the thalamus in all 41 hemispheres (100%), compared to 96 of the 197 hemispheres (49%) without a fetal type circle of Willis (p<0.01). In patients with a hypoplastic A1 segment, there was more often a contribution of the contralateral ICA to the ipsilateral deep brain structures.

15:00         4071.     A Comparison of 3D-GRASE and EPI for Vessel-Encoded Arterial Spin Labeling

Thomas William Okell^1,2, Michael Chappell¹, Matthias Günther^3,4, Peter Jezzard¹

¹FMRIB Centre, Clinical Neurology, University of Oxford, Oxford, Oxfordshire, United Kingdom; ²Department of Medical Physics and Clinical Engineering, Oxford Radcliffe Hospitals NHS Trust, Oxford, Oxfordshire, United Kingdom; ³Faculty for Physics and Electrical Engineering, University Bremen, Bremen, Germany; ⁴Fraunhofer MEVIS-Institute for Medical Image Computing, Bremen, Germany

In this study we compare echo planar imaging (EPI) and 3D-GRadient and Spin Echo (3D-GRASE) readouts with a vessel encoded arterial spin labelling preparation.  Comparable vascular territory maps were obtained in both cases.  The 3D-GRASE images had twice the signal-to-noise ratio and reduced signal drop-out but suffered from some blurring in the slice direction despite the use of parallel acceleration in one dimension.  We conclude that 3D-GRASE is a viable option for vascular territory imaging but would be improved by reduced blurring which could be achieved by using parallel acceleration in two dimensions, for example.

ASL:  Applications & Reproducibility

14:00         4072.     Cerebral Autoregulation Impairment Measured at the Brain Tissue Level with Arterial Spin Labeling MRI in Patients with a Symptomatic Carotid Artery Stenosis - not available

Reinoud Pieter Harmen Bokkers¹, Matthias J.P. van Osch², H Bart van der Worp³, Gert J. de Borst⁴, Willem P Th M Mali¹, Jeroen Hendrikse¹

¹Department of Radiology, UMCU, Utrecht, Netherlands; ²Department of Radiology, LUMC, Leiden, Netherlands; ³Department of Neurology, UMCU, Utrecht, Netherlands; ⁴Department of Vascular Surgery, UMCU, Utrecht, Netherlands

Patients with a stenosis of the internal carotid artery have a high risk of ischemic stroke. In these patients, impairment of the vasodilatory capacity of the cerebral vasculature is an important measure of the degree of hemodynamic compromise. The aim of our study was to measure the cerebral autoregulatory status of the brain tissue supplied by the individual brain feeding arteries using arterial spin labeling MRI and to compare this to healthy controls. Our results show, that ASL is able to visualize and quantify the vasodilatory capacity in the flow territories of the major cerebral arteries at brain tissue level.

14:30         4073.     High Flavonoid Cocoa Changes Regional Cerebral Blood Flow

Laura M. Parkes^1,2, Jonathan A. Goodwin², Andrew Irwin², Roeland van Kerckhoven³, Richard Draijer³

¹Imaging Sciences, University of Manchester, Manchester, United Kingdom; ²MARIARC, University of Liverpool, Liverpool, United Kingdom; ³Unilever Research & Development, Vlaardingen, Netherlands

The aim was to investigate the effect of high-flavonoid cocoa on CBF in a group of 15 subjects using arterial spin labeling, and determine any link between CBF and cognitive performance. We used a randomized cross-over design with 2 treatments: Cocoa soy-drink and a placebo drink, each taken for two weeks with CBF and cognitive performance measured at the end of each period. Consumption of high-flavonoid cocoa increased CBF in the temporal lobe and hippocampal regions involved in long-term memory function and decreased CBF to regions involved in working memory, in agreement with cognitive results.

15:00         4074.     Resting Cerebral Blood Flow  as a Biomarker of HIV in the Brain

Jewell Thomas¹, Huiling Peng¹, Tammie Benzinger², Avi Snyder¹, David Clifford¹, Beau Ances¹

¹Neurology, Washington University in St. Louis, St. Louis, MO, United States; ²Radiology, Washington University in St. Louis, St. Louis, MO, United States

HIV causes hypoperfusion within cortical and subcortical brain structures. We used arterial spin labeling (ASL) to measure resting cerebral blood flow (rCBF) within HIV+ participants (both naïve and on stable highly active antiretroviral therapy (HAART)) and HIV- controls. HIV- controls had a significantly higher rCBF (61.7 ± 1.7 mL/100gm/min) compared to HIV+ participants (48.4 ± 1.9 mL/100gm/min). rCBF was significantly diminished in HIV+ naïve patients (44.8 ± 1.9 mL/100gm/min) compared to HIV+ subjects on stable HAART (52.6 ± 2.0 mL/100gm/min). Our results suggest that rCBF may provide a sensitive biomarker for efficacy of HAART in the brain of HIV+ participants.

15:30         4075.     Hemodynamic Characterization of Dementias Via Pseudo Continuous ASL

Simone Chaudhary^1,2, Rafal Janik¹, Amy Scouten¹, Adrienne Dorr¹, Wayne Lee³, Graeme Schwindt¹, Sandra Black¹, John Sled³, Bojana Stefanovic¹

¹Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; ²Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; ³Hospital for Sick Children, Toronto, Ontario, Canada

A number of neurodegenerative diseases are characterized by compromised cerebral hemodynamics. Cerebral blood flow (CBF) and arterial transit time have been mapped in healthy elderly, MCI, and AD via pulsed continuous ASL at varying inversion times. Two compartment theory was employed in the analysis. MCI showed a trend toward decreased CBF relative to healthy volunteers, whereas AD was associated with a pronounced, statistically significant hypoperfusion. Arterial transit time decreases suggested compensatory vasodilation in a subset of subjects.

13:30         4076.     Effect of Arterial Blood Signal Measurements on the Repeatability and Accuracy of Whole Brain CBF Values with 3D-PULSAR Imaging

Neville D. Gai¹, Sardha L. Talagala², John A. Butman¹

¹Radiology & Imaging Sciences, National Institutes of Health, Bethesda, MD, United States; ²NINDS, National Institutes of Health, Bethesda, MD, United States

3D-PULSAR and 3D-IR-PULSAR provide whole brain perfusion imaging in about 5 minutes. Quantification of CBF is done using the Buxton model in conjunction with a QUIPSS II saturation pulse to define bolus length. Measurement of the arterial blood signal (M_0A)is considered the single most important factor affecting accuracy and repeatability of CBF values in such a model. We investigated repeatability across volunteers with and without this source of error. It is shown that M_0A does not contribute significantly more than other sources of errors as long as parial volume and saturation effects are avoided. In addition, experiments with the same volunteers and different sessions provided average CBF values that were within 3% of each other.

14:00         4077.     Measurement Stability in Arterial Spin Labeling Investigated Using Multiple Sites

Jerod Michael Rasmussen¹, Tom Liu², Bryon Mueller³, Greg Brown², Christina Wierenga², Gary H. Glover⁴

¹University of California, Irvine, Irvine, CA, United States; ²University of California, San Diego; ³University of Minnesota; ⁴Stanford University

This study uses multiple scanners to investigate the effect of varying the number of repetitions used in CBF measurement of Gray Matter tissue (GM) and establishes recommendations for the minimum scan time necessary for a stable calculation. Data was combined across 2 traveling subjects studies and the number of repetitions used for analysis ranged from 16 to 104 in control/tag pairs. Gray Matter masked CBF statistics showed an expected inverse decrease in noise with acquisitions and converged on a recommendation of 92 repetitions for a stable CBF measurement.

14:30         4078.     Comparison of Reproducibility Between Continuous, Pulsed, and Pseudo-Continuous Arterial Spin Labeling

Yufen Chen¹, Jiongjiong Wang¹, Marc Korczykowski¹, Maria Fernandez-Seara², John A. Detre¹

¹Center of Functional Neuroimaging, University of Pennsylvania, Philadelphia, PA, United States; ²Center for Applied Medical Research, University of Navarra, Pamplona, Navarra, Spain

Pseudo-continuous arterial spin labeling is a recent addition to the family of ASL methods that combines the high signal-to-noise ratio (SNR) of continuous methods and the lower duty cycle of pulsed methods. To date, no formal within- and across-session comparison between the methods has been performed. Here, we compare the reproducibility of three variants of ASL: continuous, pulsed and pseudo-continuous. Our results demonstrate that pCASL and PASL have the lowest degree of variations (~13%) in scans repeated after one week, pCASL also has higher temporal SNR, which makes it a favorable method for measuring cerebral blood flow.

15:00         4079.     Regional Distribution, Laterality, and Reliability of Volumetric Cerebral Perfusion Imaging in Healthy Adults

Adolf Pfefferbaum^1,2, Ajit Shankaranarayanan³, David Alsop^4,5, Sandra Chanraud, ^1,2, Anne-Lise Pitel², Torsten Rohlfing¹, Edith V. Sullivan²

¹Neuroscience Program, SRI International, Menlo Park, CA, United States; ²Psychiatry&Behavioral Sciences, Stanford University, Stanford, CA, United States; ³MR Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States; ⁴Radiology, Harvard Medical School, Boston, MA, United States; ⁵Radiology, Beth Israel Deaconess Medical Center, Boston, m, United States

The regional distribution, laterality and reliability of volumetric arterial spin labeling (ASL) measurements of CBF in cortical, subcortical, and cerebellar regions was determined in normal volunteers. Regional CBF, normalized for global perfusion, was highly reliable when measured on separate days. There was considerable regional variability and several regions of significant lateral asymmetry. The posterior cingulate cortex had the highest perfusion and the globus pallidus the lowest, may be due to iron-induced signal attenuation. High rCBF in the posterior cingulate cortex in this task-free acquisition is consistent with its identification as a principal node of the "default mode network."

13:30         4080.     Comparison Between Total CBF Values Measured by ASL and Phase Contrast Over Increased Range of CBF Values - not available

Noam Alperin¹, Murat Bagci, Sang H. Lee, Lara Eftimov², Birgit Ertl-Wagner²

¹University of Miami, Miami, FL, United States; ²University of Munich, Germany

ASL utilizes the water in arterial blood as endogenous contrast agent to assess cerebral blood perfusion and therefore is becoming more commonly used. A perfusion image is generated by subtracting a tagged image from a control image, where the tagged image is acquired following the “labeling” of the blood upstream. The time delay between the labeling and the image acquisition is the transient time. The choice of this delay can affect the derived CBF values. This project aims to compare between measurements of total CBF obtained with ASL and phase contrast MRI. The comparison was done over a wide range of CBF values by manipulating the subjects end tidal pCO2 level. Results from this comparison suggest that the PC based tCBF values could be used for “calibrations” of relative ASL derived CBF values.

14:00         4081.     Comparison of Arterial Transit Times Estimated Using FEAST and LL-FAIR

Yufen Chen¹, jiongjiong Wang¹, Marc Korczykowski¹, John A. Detre¹

¹Center of Functional Neuroimaging, University of Pennsylvania, Philadelphia, PA, United States

Arterial transit time is a physiological parameter measured by arterial spin labeling. Look-locker (LL-FAIR) and Flow Encoded Arterial Spin Tagging (FEAST) are two ASL variants that can quantify arterial transit time. Comparison of the estimated arterial transit times show good correlation between the two methods in gray matter of major vascular regions (r=0.46, p=0.02), despite a difference of ~1s. This is because FEAST is sensitive to arterial transit time to tissue, while LL-FAIR measures the arrival of labeled blood in the imaging slice. Combination of the two can improve understanding of pathology of cerebrovascular diseases.

14:30         4082.     The Porcine Kidney as a Biological Phantom for MR ASL Perfusion Measurements

Keith Heberlein¹, Ulrike Haberland¹, Ernst Klotz¹, Micahel Lell²

¹Siemens AG, Healthcare Sector, Erlangen, Germany; ²Oberarzt Radiologisches Institut, Universitätsklinikum Erlangen

The porcine kidney is an effective biological phantom due to a dense capillary system, high rates of in vivo perfusion and an accessible vascular supply which is integrated easily into a flow circuit. This work demonstrates ASL based perfusion imaging and reproduces previous results based on CT dye dilution perfusion measures. A robust, stable model for multi-modality imaging of perfusion is presented.

15:00         4083.     Perfusion Imaging of the Human Cervical Spinal Cord

Govind Nair¹, Xiaoping P. Hu¹

¹Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, Atlanta, GA, United States

Perfusion imaging of the cervical cord, while challenging due to anatomical constraints and pattern of blood flow, may prove to be valuable in diagnosing and evaluating pathologies like ischemia, tumor and neurodegeneration. In this study, perfusion imaging of the cervical enlargement was performed on healthy human subjects using pulsed ASL technique with varying inversion times. We estimate an arterial transit time of 2s and observed the peak perfusion signal at 4s from the inversion pulse. The quantitative spinal cord perfusion rate was determined to be 26±11 ml/100g/min, which was lower than those in the brain.

13:30         4084.     Increased Basal Ganglia Metabolism by the Dopamine Antagonist Metoclopramide  Measured by Perfusion MRI

Maria Asuncion Fernandez-Seara¹, Maite Aznarez-Sanado¹, Franz Heukamp², Maria Asuncion Pastor¹

¹Neuroscience, Center for Applied Medical Research. University of Navarra, Pamplona, Navarra, Spain; ²IESE Business School. University of Navarra

The effects on cerebral perfusion of an oral dose of the dopamine antagonist antiemetic Metoclopramide were assessed in a group of young healthy volunteers, using phase contrast imaging and arterial spin labeling perfusion MRI. Metoclopramide significantly reduced mean blood velocity and blood flow through the internal carotid arteries and cerebral blood flow in distributed areas of the cortex. However, Metoclopramide intake selectively increased perfusion in the striatum. A similar perfusion pattern has been observed in patients with Parkinson´s disease. Our results suggest that hyperperfusion in the striatum could be a very early marker of PD and that ASL perfusion MRI could aid in the early diagnosis of the disease.

14:00         4085.     Quantification of Cerebral Blood Flow, Oxygen Extraction Fraction, and Oxygen Metabolic Index in Human with Inhalation of Air and Carbogen

Hongyu An¹, Souvik Sen¹, Yasheng Chen¹, William Powers¹, Weili Lin¹

¹University of North Carolina at Chapel Hill, Chapel Hill, NC, United States

In this study, we have demonstrated that using CASL and ASE methods, CBF and OEF can be consistently measured in human under repeated air and carbogen inhalation.  In agreement with previous PET study, an increase of CBF along with a reciprocal decrease of OEF, and an unchanged OMI were detected with carbogen inhalation.

14:30         4086.     Comparison of Cerebral Blood Flow Using Arterial Spin Labeling and Phase Contrast Angiography Under Hyperoxia and Hypercarbia.

John Robert Cain¹, Samantha J. Mills¹, Alan Jackson¹, Laura M. Parkes^1,2

¹Imaging Science, University of Manchester, Manchester, United Kingdom; ²Biomedical Imaging Institute, University of Manchester, Manchester, United Kingdom

Four healthy subjects (aged 24-29) underwent MRI imaging, inhaling 100% O₂, medical air and carbogen gas (95%O₂ 5%CO₂). Imaging consisted of STAR ASL sequence followed by a PCA acquisition under each gas. CBF values were higher during carbogen inhalation compared to medical air with both PCA and ASL. 100% O₂ CBF results were not significantly different from medical air using both methods but the difference between the ASL label and control signal (ΔM) was decreased compared to medical air and increased during CO₂ inhalation. ASL was able to detect changes in CBF with equal precision to PCA CBF measurements.

15:00         4087.     Human Retinal Blood Flow MRI Using Pseudo-Continuous Arterial Spin Labeling and Balanced Steady State Free Precession

Sung-Hong Park¹, Yi Zhang¹, Jinqi Li¹, Qi Peng¹, Jiongjiong Wang², Timothy Q. Duong¹

¹Research Imaging Institute, Ophthalmology/Radiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States; ²Radiology and Neurology, University of Pennsylvania, Philadelphia, PA, United States

Mapping human retinal blood flow has not been easy with EPI-based arterial spin labeling (ASL) techniques because of significant susceptibility effects around eyes. In this study, we propose to use a combination of pseudo-continuous ASL and balanced steady state free precession (bSSFP) readout for mapping blood flow in the human retina. The results showed reproducible human retinal blood flow, free of motion artifacts, image distortion, signal drop out and bSSFP banding artifacts.

Dynamic Contrast Enhancement MRI

14:00         4088.     Design and Testing of a Phantom for Calibration of MRI Systems Used in DCE-MRI Clinical Trials

Michael H. Buonocore¹, David H. Gultekin², Michael A. Jacobs³, Steffen Sammet⁴, Natarajan Raghunand⁵, Joshua Levy⁶, Michael V. Knopp⁴

¹Radiology, UC Davis Imaging Research Center, Sacramento, CA, United States; ²Memorial Sloan-Kettering Cancer Center, New York, NY, United States; ³Radiology, Johns Hopkins University, Baltimore, MD, United States; ⁴Radiology, Ohio State University, Columbus, OH, United States; ⁵Radiology, University of Arizona, Tucson, AZ, United States; ⁶The Phantom Laboratory, Inc., Salem, NY, United States

This study presents a new DCE-MRI phantom designed for calibration of MRI systems to be used in multi-site clinical trials. Preliminary results at four clinical sites show the ability of the phantom to reveal critical similarities but also expected and unexpected differences in the images and derived DCE-MRI parameters.

14:30         4089.     Monte Carlo Simulation to Study the Robustness of Empirical DCE-MRI Kinetic Parameters to Gaussian Noise

Ka-Loh Li¹, Alan Jackson¹, Gerard Thompson¹, Xiaoping Zhu¹

¹Imaging Science and Biomedical Engineering, The University of Manchester, Manchester, United Kingdom

Using empirical descriptors to assess T1-weighted DCE-MRI data is easy to perform. However, the effects of MRI noise on the reliability of empirical kinetic parameters have not been systematically investigated. This study investigated the robustness of several empirical parameters to Gaussian noise under various pharmacokinetic and noisy conditions using Monte Carlo simulation. We found that area under the enhancement curves was most robust to Gaussian noise. Signal enhancement ratio is mostly sensitive to noise and pharmacokinetic conditions. The study improved our understanding of the noise effect on empirical kinetic parameters, leading to better interpretation of these parametric images.

15:00         4090.     Optimal Period of Linearity Using Patlak Analysis in Brain Tumors

Rajan Jain¹, Hassan Bagher-Ebadian^2,3, Jayant Narang¹, Siamak Pourabdollah Nejad-Davarani², Sona Sakesna¹, Lonni Schultz⁴, Mohammad H. Asgari², James R. Ewing^2,3

¹Radiology, Henry Ford Hospital, Detroit, MI, United States; ²Neurology, Henry Ford Hospital, Detroit, MI, United States; ³Physics, Oakland University, Rochester, MI, United States; ⁴Biostatistics and Research Epidemiology, Henry Ford Hospital, Detroit, MI, United States

In Patlak analysis, contrast agent transport is assumed to be unidirectional (from plasma space into extracellular extravascular space). Although this model has the advantage of simplicity, it is important to note that it will give inaccurate results when this assumption is incorrect as in leaky brain tumors. Using longer acquisition fit-times will probably yield overestimates of fV and underestimates of Ktrans in the leaky regions as these will fall into the non-linear part of the Patlak plot. Hence, understanding of the optimal fit-times as well as proper modeling used for Patlak analysis is important for measuring the physiologic parameters accurately.

15:30         4091.     The Patlak Plot in MRI Pharmacokinetic Analysis

Charles S. Springer, Jr. ¹, William D. Rooney¹, Xin Li¹

¹Advanced Imaging Research Center, Oregon Health & Science University, Portland, OR, United States

An honored method for pharmacokinetic interpretation is the Patlak Plot – the popular linearization technique introduced over 25 years ago for graphical tracer data analyses.  In (Dynamic-Contrast-Enhanced) DCE-MRI, the injected contrast reagent (CR) plays the tracer role.  However, there are crucial differences between the molecular mechanisms underlying the detection of tracers and CRs.  This contribution discusses how these differences impact the use of the Patlak Plot for the analysis of DCE-MRI data.

13:30         4092.     Background Correction of Phase-Based Arterial Input Functions

Anders Garpebring¹, Patrik Brynolfsson¹, Ronnie Wirestam², Nils Östlund³, Mikael Karlsson¹

¹Radiation Sciences, Umeå University, Umeå, Sweden; ²Medical Radiation Physics, Lund University, Lund, Sweden; ³Biomedical Engineering and Informatics, Umeå University Hospital, Umeå, Sweden

Phase sensitive MRI has shown great potential for quantification of the Arterial Input Function (AIF). However, motion induced phase artefacts are problematic for in-vivo measurements and must be compensated for. The purpose of this study was to compare three different background ROI selection procedures for compensation of phase errors. Results showed that efficient correction of motion induced phase shifts requires a background ROI placed close to the vessel from which the AIF is sampled. Some further improvement can also be achieved by tracking and compensating for any in-plane motion of the vessel.

14:00         4093.     Preliminary Results with 3D DCE-MRI Curve Pattern Analysis of Treatment Response in Osteosarcoma

Junyu Guo¹, Qing Ji¹, Mary E. McCarville¹, Najat C. Daw², Wilburn E. Reddick¹

¹Radiological Science, St Jude Children's Research Hospital, Memphis, TN, United States; ²Department of Oncology, St Jude Children's Research Hospital, Memphis, TN, United States

A new osteosarcoma treatment protocol in our Institute includes a multiagent chemotherapy with an anti-angiogenic agent (bevacizumab). Serial DCE-MRI was performed at six different time points during neoadjuvant therapy, and a recently developed DCE-MRI data analysis method, the CPA method, was used to process the data and assess treatment response in the first eight patients. According to our preliminary results, it is feasible to assess the tumor treatment response to neoadjuvant therapy using the CPA method in DCE-MRI. Further investigation of this CPA method on a larger cohort of patients will be performed.

14:30         4094.     The Effect of Blood Inflow and B₁-Field Inhomogeneity on Measurement of the AIF in Axial 3-D SPGR DCE-MRI

Caleb Roberts^1,2, Ross A. Little^1,2, Yvonne Watson^1,2, Sha Zhao^1,2, David L. Buckley³, Geoff J M Parker^1,2

¹Imaging Science and Biomedical Engineering, The University of Manchester, Manchester, United Kingdom, United Kingdom; ²The Biomedical Imaging Institute, The University of Manchester, Manchester, Greater Manchester, United Kingdom; ³Division of Medical Physics, University of Leeds, Leeds, United Kingdom

A major potential confound in axial 3-D dynamic contrast-enhanced MRI (DCE-MRI) studies is the blood inflow effect and therefore the choice of slice location for arterial input function (AIF) measurement within the imaging volume must be considered carefully.  Using a combination of computer simulations, flow phantom and in vivo studies we describe and understand the effect of blood inflow on the measurement of the AIF.  We demonstrate that reliable AIFs are achievable in 3-D DCE-MRI but the use of inflow affected AIFs in tracer kinetic modeling result in large errors in tissue microvascular parameters.

15:00         4095.     Introducing New DCE Parametric Maps to Quantify Vascular Changes Induced by the Anti-Angiogenic Drug Sunitinib

Areen Al.Bashir^1,2, Gilda Hillman³, Meng Li², Yashwanth Katkur², E. Mark Haacke^1,2

¹Department of Biomedical Engineeringt, Wayne State University, Detroit, MI, United States; ²Department of Radiology, Wayne State University, Detroit, MI, United States; ³Department of Radiation Oncology, Wayne State University

DCE-MRI has been routinely used to quantify the effectiveness of new anti-angiogenic drugs on the tumor vasculature using Gd-DTPA as a contrast agent. However, this quantification is not easy. DCE has a lot of parameters that make it a very complex technique, such as finding AIF and choosing the pharmacokinetic model. Hence, in this study, we introduced the new DCE parametric maps which was calculated from Gd concentration, C(t), data. Regional analysis were preformed on 4 groups of mice treated with different dose of the anti-angiogenic drug, sunitinib, and the results compared. Our results demonstrate that DCE parametric maps have the potential to quantify the effect of new anti-angiogenic drugs on tumor and normal tissues. These findings were confirmed with histological observations.

13:30         4096.     Evaluation of Tracer Kinetics Parameters in Brain Gliomas Using Combined T1W and T2*W Contrast-Enhanced Dynamic MR Imaging: Comparison with Pathological Findings - not available

Keiichi Kikuchi¹, Shohei Kouno², Hitoshi Miki¹, Shogo Oda¹, Teruhito Mochizuki¹, Shiro Ohue², Kenya Murase³

¹Radiology, Ehime University, Toon City, Ehime, Japan; ²Neurosurgery, Ehime University, Toon City, Ehime, Japan; ³Medical Engineering, Osaka University, Suita, Osaka, Japan

We evaluated various tracer kinetics parameters of brain gliomas using combined DCE-MRI and DSC-MRI in one examination. The tracer kinetics parameters are high in grade IV gliomas; especially the K1 value has a significant correlation with MIB-1 and MVD. These parameters derived from DSC-MRI and DCE-MRI should be correlated with the tumor vascularity and/or tissue permeability, and will provide additional information for diagnosis and prediction prognosis. Our protocol, which can derive the various tracer kinetics parameters of brain tumors in one examination, will be a promising protocol to evaluate the characteristics of brain tumors.

14:00         4097.     Quantitative Analysis of Perfusion Parameters in Osteoporotic Patients with Acute Vertebral Fracture Using Dynamic-Contrast-Enhanced MRI

Gerwin P. Schmidt¹, Andreas Biffar, Steven P. Sourbron, Melvin D'Anastasi, Mike Notohamiprodjo, Maximilian F. Reiser, Andrea Baur-Melnyk

¹Department of Radiology, University Hospitals Munich, Munich, Bavaria, Germany

The analysis of dynamic contrast-enhanced data provides reproducible quantitative perfusion parameters in healthy and pathologic bone marrow. Perfusion is strongly increased in acute osteoporotic fractures yielding areas of different perfusion parameters, potentially representing different sites of reactive and reparative process. Furthermore, perfusion parameter changes correlate with severity of osteoporosis and may serve as a tool to differentiate various stages of the disease.

14:30         4098.     Qualitative and Quantitative Assessment of Osteosarcoma Treatment Response Using DCE-MRA

Junyu Guo¹, Wilburn E. Reddick¹

¹Radiological Science, St Jude Children's Research Hospital, Memphis, TN, United States

A DCE-MRA method is presented to provide a new way of rendering DCE-MRI data, which greatly simplifies the process for the large volume of DCE-MRI data and enables qualitative and quantitative assessment of the treatment response. The qualitative DCE-MRA method provides a simple and quick way for a radiologist to make an overall assessment of tumor response to neoadjuvant chemotherapy. This method makes it potentially possible for a radiologist to identify a likely nonresponder. The quantitative measures were evaluated and the shape of plot curves of the two patients was consistent with that from direct observation of MIP images.

15:00         4099.     Evaluating the Response to the Radiation Therapy of the Head and Neck Neoplasms by Dynamic Contrast-Enhanced MRI

Shin-Lei Peng¹, Chih-Feng Chen², Ho-Ling Liu³, Fu-Nien Wang¹

¹Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan, Taiwan; ²Department of Radiology, Chang Gung Memorial Hospital Kaohsiung Medical Center, Kaohsiung, Taiwan, Taiwan; ³Medical Imaging and Radiological Sciences , Chang Gung University, Taoyuan, Taiwan, Taiwan

Most of the DCE-MRI studies analyzed averaged signal time curves from a tumor region in a single slice. However, the averaged signal could not totally represent the heterogeneity of the whole tumor. The goal of this study was analyzing the histogram distribution of all initial slopes of enhancement from pixel-by-pixel signal time curves and distinguishing the malignant tumor from radiation necrosis in the hand and neck neoplasms. And the results show that the histogram distribution improved the specificity of diagnosis and provided the information about the heterogeneity of tumor compositions.

13:30         4100.     Direct Measurement of Arterial Input Function in White Matter

Vishal Patil¹, Jens H. Jensen¹, Glyn Johnson¹

¹Radiology, NYU School of Medicine, New York, United States

Estimating the arterial input function (AIF) is the first step in most DSC and DCE MRI analyses. Problems associated with measuring an AIF in a large vessel are partially resolved by AIF measurements in normal white matter. However, an accurate relationship between relaxivity and contrast agent concentration, C, has never been determined in white matter in vivo. In this study we compared AIFs derived from blood and white matter using two relaxivity models: 1) A nonlinear model which interpolates between both short and long static dephasing regime times. 2) A linear model while only considers long dephasing times. The results demonstrate that the nonlinear model provides an accurate relationship between relaxivity and C.

14:00         4101.     Nonlinear Partial Volume Effects in DCE-MRI

Matthias C. Schabel¹, Edward V R DiBella¹

¹Radiology/Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, United States

In the presence of partial voxel blood volume, conventional quantitative methods of converting signal to concentration in DCE-MRI result in significant biases in pharmacokinetic parameter estimates. Direct modeling and nonlinear regression of signal dependence on concentration avoids these biases, giving accurate and unbiased parameter estimates.

14:30         4102.     Non-Linear Contrast Agent Relaxivity and the Accuracy and Sensitivity of DCE MRI Measurements

Vishal Patil¹, Glyn Johnson¹

¹Radiology, NYU School of Medicine, New York, United States

DCE MRI is increasingly used to determine the prognosis and diagnosis of various pathologies. The accuracy of DCE MRI parameter estimates is dependent on a variety of factors including the relationship between relaxivity and contrast agent concentration, C. Recent studies have demonstrated that relaxivity is not linearly dependent on C but is more accuratly described by a quadratic model. In this study we investigate the effect of neglecting non-linear components on DCE MRI parameter estimates derived using a Tofts/Kety model with both T₁ and T₂*-weighted protocols.

15:00         4103.     Optimal Flip Angle Set in Spoiled Gradient-Echo MR Imaging Technique

Hassan Bagher-Ebadian^1,2, Ramesh Paudyal¹, Rajan Jain³, Jayant Narang³, James Russle Ewing^1,2

¹Neurology, Henry Ford Hospital, Detroit, MI, United States; ²Physics, Oakland University, Rochester, MI, United States; ³Radiology, Henry Ford Hospital, Detroit, MI, United States

In spoiled gradient echo sequences, the T1-weighting of image contrast is strongly affected by a nonlinear interaction of two sequence parameters, repetition time (TR) and flip angle (á) . Since the T1 is filed dependant, optimal set of á is chosen to produce a field-dependent contrast behavior in MR imaging. Therefore, a pulse sequence with an optimal set of flip angle which provides a best Signal-to-Noise ratio would be useful in various quantitative methods. In the proposed study, a set of optimal flip angles which yield a better tissue contrast at different magnetic field strengths (3T, 7T) is determined.

DSC Perfusion

14:00         4104.     Comparison of Different Algorithms for Minimizing Macro Vessel Signal in Cerebral Perfusion Imaging

Gernot Reishofer¹, Karl Koschutnig², Christian Enzinger³, Stefan Ropele³, Franz Ebner²

¹Radiology, Medical University Graz, Graz, Austria; ²Neuroradiology, Medical University Graz; ³Neurology, Medical University Graz

Parameter values obtained by DSC-MRI are often overestimated compared to PET and SPECT, which is due to the high sensitivity of DSC-MRI to large vessel. Two methods for minimizing macro vessel signal are compared in this work. First, the ICA method which is based on the separation of independent flow patterns using independent component analysis and second, the ELV method which is based on clustering of parameters derived from the dynamic contrast-enhanced first-pass curve. Our results indicate that the ICA method has some advantages over the ELV method and should be preferred for minimizing macro vessel signal in DSC-MRI data.

14:30         4105.     Tissue Similarity Map of High Resolution Perfusion Weighted MR Imaging of the Brain

Meng Li¹, Areen Bashir¹, Yanming Yu², Yang Xuan¹, Zahid Latif¹, James Garbern¹, Jiani Hu¹, E M. Haacke^1,3

¹Wayne State University, Detroit, MI, United States; ²Peking University, Beijing, China; ³MRI Institute of Biomedical Research, Detroit, MI, United States

Tissue similarity map (TSM) is a new approach to reveal the brain tissue perfusion status directly from their signal intensity time course characteristics s(t) rather than indirectly through the concentration time curve c(t). It avoids the need for defining AIF as well. The purpose of this study is to use high resolution perfusion weighted MR imaging to create a tissue similarity map to demonstrate the differences in perfusion between tissues and inter-tissue. It may have immediate applications in clinic.

15:00         4106.     Voxel-Specific Brain Arterial Input Functions from DSC-MRI and Blind Deconvolution in a Group of Healthy Males

Renate Gruner^1,2, Håkon Nordli¹, Gunnar Moen¹, Torfinn Taxt^1,2

¹Haukeland University Hospital, Bergen, Norway; ²University of Bergen, Norway

Voxel specific arterial input functions were estimated in a group of 44 healthy males using a recently published blind deconvolution approach in order to investigate how the estimated functions varied across participants and brain regions. Qualitatively, variations in arterial input functions were consistent with expectations of normal vascular supply. The quantitative differences in the arterial input functions between brain regions suggested that the functions could be useful in reducing delay and dispersion effects in cerebral flow estimates. Differences in delays and dispersion were larger within one brain region across participants, than across regions within one participant.

15:30         4107.     Performance Analysis of the Inline Quantitative Cerebral Perfusion Measurements with MR

Anindya Sen¹, Sameer Maheshwari¹, Jessy J. Mouannes², Chris Eddleman³, Sven Zuehlsdorff⁴, Saurabh Shah⁴, Timothy J. Carroll^1,2

¹Radiology, Northwestern University, Chicago, IL, United States; ²Biomedical Engineering, Northwestern University, Chicago, IL, United States; ³Neurological Surgery, Northwestern University; ⁴CMR Research and Development, Siemens Healthcare, Chicago, IL, United States

The American Heart Association has deemed the quantification of cerebral perfusion in stroke to be of paramount importance. Hence accurate automated determination of perfusion image maps are essential for analyzing the tissue of risk after an ischemic stroke event.  The need for offline post-processing of Dynamic Susceotibility Contrast (DSC) images can delay the availability of time critical information (i.e. the extent of the perfusion diffusion mismatch predicts the response to intra venous thrombolysis in ischemic stroke) Therefore we have developed a inline protocol to eliminate the offline generation of quantitative perfusion maps with evaluation.

13:30         4108.     A Method to Remove Large Blood Vessel Contribution in Brain Tumor Perfusion Imaging

Kelvin K. Wong^1,2, Hui You³, Geoffrey S. Young^3,4, Stephen TC Wong^1,2

¹Department of Radiology, The Methodist Hospital Research Institute, Houston, TX, United States; ²Department of Radiology, Weill Cornell Medical College, New York, United States; ³Department of Radiology, Brigham and Women's Hospital, Boston, MA, United States; ⁴Department of Radiology, Harvard Medical School, Boston, MA, United States

Regional cerebral blood volume is a useful marker for brain tumor evaluation.  However, large blood vessels also contribute to high blood volume, which may have nothing to do with tumor angiogenesis.  Prior studies focused on multi-parametric methods to remove a blood vessel which is complex to implement and have a lot of assumptions in the automatic identifications. We propose a simple method to identify the regions affect by large blood vessels using a blood flow map generated by a novel deconvolution technique and successfully identifies the blood vessel contribution in the tumor blood volume map.

14:00         4109.     Quantification of Vessel Permeability with Dynamic Susceptibility Contrast MRI

Yen-Peng Liao¹, Yi-Ying Wu², Yuan-Yu Hsu³, Yau-Yau Wai, ^1,4, Ho-Ling Liu^1,4

¹Department of Medical Imaging and Radiological Sciences, Chang Gung University, Taoyuan, Taiwan; ²Department of Radiology, Taichung Veterans General Hospital, Taiwan; ³Department of Medical Imaging, Buddhist Tzu Chi General Hospital, Taipei, Taiwan; ⁴Division of Medical Imaging and Intervention, Chang Gung Memorial Hospital, Taoyuan, Taiwan

In DSC-MRI, the leakage of contrast agent which results in additional T1 and T2* relaxation effects in disrupted BBB causes the contamination of T2*-weighted signal.  The relative CBV (rCBV) may be overestimated with uncorrected signal information.  This phenomenon can be described with a theoretical model considered T1 and T2* relaxation effects and the rCBV can be corrected.  Based on the model, the T1 of pre-contrast tissue measurement was an essential parameter for quantifying permeability surface area product (PS).  This study provides a method for absolutely quantification of PS.  The results showed comparable values to those in literatures.

14:30         4110.     Assessment of the Vascularity of Glioblastoma Multiforme Using Alternate-Echo Multislice Perfusion-Weighted MRI with the First-Pass Pharmacokinetic Model

Tatsuya Yamamoto¹, Hidemasa Uematsu¹, Hiroaki Takeuchi², Hirohiko Kimura¹

¹Department of Radiology, University of Fukui, Fukui, Japan; ²Department of Neurosurgery, University of Fukui, Fukui, Japan

T1 shortening effect due to the leakage of contrast agent causes underestimation of the tumor vascularity using single-echo perfusion-weighted MR imaging. On the other hand, T2* shortening due to contrast material present in the extravascular space causes overestimation. To incorporate the effects of the extravascular compartment containing contrast material residue, pharmacokinetic modeling with two compartments: the intravascular space; and the extravascular space: is required. We demonstrate here that the combination of an alternate-echo, single shot SPIRAL acquisition and first-pass pharmacokinetic model can correct for the T1 shortening effect, as well as for the T2* shortening in order to evaluate the exact tumor vascularity of enhancing glioblastoma multiforme.

15:00         4111.     Intraoperative DSC-MRI (IDSC-MRI): Feasibility and Clinical Application

Stephan Ulmer¹, Gesa Hartwigsen², Michael Helle¹, Olav Jansen¹, Maximillian Hubertus Mehdorn³, Arya Nabavi³

¹Institute of Neuroradiology, University Hospital of Schleswig-Holstein, Kiel, Germany; ²Department of Neurology, University Hospital of Schleswig-Holstein, Kiel, Germany; ³Department of Neurosurgery, University Hospital of Schleswig-Holstein, Kiel, Germany

Dynamic susceptibility contrast MRI (DSC-MRI) was applied in a model with an air-fluid-level and in a flow phantom to assess possible artifacts of an intraoperative setting. In 6 patients with glioblastoma multiforme iDSC-MRI was performed. In both models there were only minor distortions. In 5 patients complete removal of the lesion was already achieved by the time of iDSC-MRI. In the remaining case tumor could be depicted that demonstrated identical perfusion ratio as in the preoperatively acquired scans. DSC-MRI is technically feasable intraoperatively and enables a differentiation of residual tumor from contrast-enhancement caused by surgical manipulation in these intraoperative MRIs.

13:30         4112.     Comparison of Cerebral Blood Volume and Contrast Leakage Correction Efficiency with Dynamic Susceptibility Contrast Enhanced Perfusion Imaging - not available

Hiroyuki Kabasawa¹, Malancha Hore², Patrice Hervo³, Tetsuji Tsukamoto¹

¹Japan Applied Science Laboratory, GE Healthcare Japan, Hino, Tokyo, Japan; ²MR Engineering, GE Healthcare, Bangalore, India; ³MR Clinical Development, GE Healthcare, Buc, France

Post-processing correction methods have been proposed to correct this contrast leakage effect in disrupted BBB and to obtain accurate CBV estimation from DSC data. The estimated leakage effect from DSC can vary with the reference time course used in the post-processing. Here, we evaluated the impact of reference time course to estimate the leakage effect using numerical simulation and clinical data. This study showed that appropriate selection of reference time course is an important factor to obtain reasonable contrast leakage index using DSC MRI. Reference time course with wider width may introduce false positive signal in leakage map.

14:00         4113.     Comparison of a Data Processing Method Accounting for Contrast Agent Extravasation with the Pre-Load Approach in Bolus-Based CBV Estimates in Tumors

Irène Troprès^1,2, Nicolas Pannetier, ²³, Sylvie D. Grand, ^2,4, Alexandre Krainik, ^2,4, Jean-François Le Bas, ^2,4, Emmanuel L. Barbier, ²³

¹Unité IRM 3T, IFR1, La Tronche - Grenoble, France; ²Universite Grenoble 1, Grenoble, France; ³U836, INSERM, Grenoble, France; ⁴Neuroradiology, Grenoble Hospital, Grenoble, France

Estimate of relative Cerebral Blood Volume (rCBV) obtained with DSC methods suffers from contrast agent (CA) extravasation in brain tumors. The aim of this study is to compare a data processing method accounting for CA dilution with the pre-load approach. In nine patients, a DSC protocol was performed twice within the same session. A gamma-variate fit was used to compute rCBV maps, with and without considering the dilution. This study suggests that the dilution method is relevant when CA pre-load is performed and that normalization of rCBV estimates by white matter values should be handled with care.

14:30         4114.     Effects of Pre-Loading Dose on DSC-MRI with Contrast Agent Extravasation

Yi-Ying Wu^1,2, Jyh-Wen Chai¹, Chi-Chang Chen¹, Ho-Ling Liu^2,3

¹Department of Radiology, Taichung Veterans General Hospital, Taichung, Taiwan; ²Institute of Medical Physics and Imaging Science, Chang Gung University, Taoyuan, Taiwan; ³MRI Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan

Disruption of blood-brain barriers in brain lesions usually causes difficulty in accurate quantification if rCBV in DSC-MRI. In this study, a simulated model was proposed to evaluate the dependence of the pre-loading dose on the rCBV measurements. The results showed an underestimate of rCBV without pre-loading or with low pre-loading dose at 1.5T. The underestimation was improved with larger pre-loading dose. Significant overestimation of rCBV happened with pre-loading of contrast agents at 3.0T, particularly with higher dose and a longer TE. In conclusion, this experiment provided important evidence that how the pre-loading dose affect the accurate quantification of rCBV measurement.

15:00         4115.     Modeling Relaxation Effects During Bolus Passage Through Leaky Vasculature Using the Finite Perturber Method - not available

David Bonekamp¹, Barney Douglas Ward², Richard Leigh³, Peter B. Barker¹, Arvind P. Pathak¹

¹Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States; ²Department of Biophysics, Medical College of Wisconsin,, Milwaukee, WI, United States; ³Department of Neurology, Johns Hopkins University, Baltimore, MD, United States

Extravasation of contrast during bolus passage alters the dynamic susceptibility contrast MRI signal. Reliable quantification of microvascular parameters in common brain pathologies depends on the ability to account for effects of leaky vasculature. Analytical solutions are hampered by mathematical approximations. We extend the computational finite perturber model (FPM) by incorporating a compartmental model to simulate arterial bolus passage and contrast agent extravasation. We find that known characteristics of DSC-MRI signal curves can be successfully modeled. This approach provides a powerful framework to optimize imaging sequences and to examine the complicated interaction of pathological, physiological and biophysical phenomena that result in the observed DSC-MRI signal.

13:30         4116.     Direct Comparison of Dynamic Susceptibility Weighted MR Perfusion with CT Perfusion in Brain Tumors

Hassan Bagher-Ebadian^1,2, Jayant Narang³, James Russel Ewing¹, Siamak Pourabdollah Nejad-Davarani^1,4, Mohammad Hossein Asgari¹, Sona Saksena³, Rajan Jain³

¹Neurology, Henry Ford Hospital, Detroit, MI, United States; ²Physics, Oakland University, Rochester, MI, United States; ³Radiology, Henry Ford Hospital, Detroit, MI, United States; ⁴Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States

The purpose of this study is comparison of Dynamic susceptibility contrast enhanced MR perfusion (DSC-MRP) and CT Perfusion (CTP) in brain tumors patients in normal as well as abnormal regions. CTP maps were calculated using the Johnson and Wilson Model and DSC-MRP maps were calculated based on conventional singular value decomposition (SVD) technique. The results imply that there is underestimation of all perfusion parameters by SVD technique as compared to CTP mostly due to the fact that DSC-MRP only measures CBV from the microvasculature as well as due to the non-linearity of arterial input function with Contrast Agent (CA) concentration.

14:00         4117.     Measuring CBV by the Recirculation Part of Dynamic Susceptibility Contrast MRI on Rat Model

Yi-Ling Wu¹, Chien-Chung Chen¹, Yi-Chun Wu¹, Chia-Hao Chang¹, Fu-Nien Wang¹

¹Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsin-Chu, Taiwan, Taiwan

Measuring Relative CBV from the recirculation part of concentration time curve is investigated on rat model.  Since the first pass of DSC method is relative fast on rat, more data points could be recruited for CBV quantification in the recirculation part.  The results showed better regression lines between MION CBV and recirculation CBV, and therefore the feasibility is proved in this study.

14:30         4118.     Quantification of Systematic Error in Standard Formula for Computing Transverse Relaxation Rates in DSC–MRI. Implications for Blood Volume and Flow Calculations

José Rufino Solera Ureña¹, Salvador Olmos¹

¹Aragon Institute of Engineering Research, Universidad de Zaragoza, Zaragoza, Spain

In dynamic susceptibility contrast (DSC) MRI experiments, the increase in the tissue transverse relaxation rate due to the passage of a bolus of intravascular paramagnetic contrast agent is routinely calculated (up to a constant) as the logarithm of the tracer dependent MR intensity normalised to baseline intensity, assuming that T1 effects are negligible. This assumption is revisited by developing the enhancement condition for a typical GE pulse sequence and the associated enhancement angle. The systematic error associated with the usual formula is analysed. Error expressions for the blood volume and flow calculations in DSC–MRI experiments are also presented and their implications discussed.

15:00         4119.     Comparison of Four Techniques That Directly Use Residue Function Characteristics When Estimating Cerebral Blood Flow During DSC MRI Studies

Michael R. Smith^1,2, Juan Qiao¹, Marina Saluzzi^1,3, Richard Frayne, ^1,3

¹Electrical and Computer Engineering, University of Calgary, Calgary, Alberta, Canada; ²Radiology, University of Calgary, Calgary, Alberta, Canada; ³Seaman Family MR Research Centre, Foothills Hospital, Calgary, Alberta, Canada

Current filtering techniques used in dynamic susceptibility contrast (DSC) studies to remove deconvolution noise are based on characteristics of the arterial signal C_a (t) and lead to CBF maps that decrease in accuracy as the tissue mean transit time (MTT) gets smaller. Our hypothesis is that greater CBF accuracy and CBF precision can be achieved by using techniques based on characteristics of the residue function; either in the time domain R(t) or in the frequency domain R(f). Of the four techniques investigated, one approach shows the most promise. This technique uses multiple points along the tissue residue function in time and frequency domains to obtain MTT estimates, and then derives CBF using CBF = CBV / MTT where CBV is the cerebral blood volume.