Importance of Different Correction Methods for Optimized 3D Visualization of 3-Directional MR Velocity Data
Ramona Lorenz¹, Jelena Bock¹, Jan Korvink², Michael Markl^1
1Dept. of Diagnostic Radiology, University Hospital, Freiburg, Germany; ²Dept. of Microsystems Technology, IMTEK, Freiburg, Germany

3D visualization of time resolved 3D phase contrast data plays an important role for the analysis of flow characteristics inside the vessels of interest. However, phase offset errors due to gradient field distortions caused by three major effects including eddy currents, concomitant gradients, and gradient field non-linearities can severely distort the measured three-directional velocities. This results in distortion of streamlines and particle traces which might lead to incorrect flow pattern visualization. The application of correction methods for all three phase offset errors resulted in an improvement of 3D streamline visualisation.

Identification of Myocardial Infarction Using Fractional Anisotropy of 3D Strain Tensors
Sahar Soleimanifard¹, Khaled Z. Abd-Elmoniem, ¹², Harsh K. Agarwal¹, Miguel Santaularia-Tomas³, Tetsuo Sasano³, Evertjan Vonken³, Amr Youssef³, M. Roselle Abraham³, Theodore P. Abraham³, Jerry Ladd Prince^1
1Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, United States; ²National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, United States; ³Cardiology Division, Department of Medicine, Johns Hopkins University, Baltimore, MD, United States

Assessment of tissue viability is currently involved with injection of gadolinium for contrast-enhanced imaging. Strain profile of myocardium has been previously studied but requires comparison of tensors fields, which is usually difficult due to multivariate nature of tensors. It is desirable to describe tensors with scalar indices, which are more mathematically and statistically intuitive. In this work, fractional anisotropy (FA) of strain tensors in healthy and infarcted regions in a large animal model is computed and compared with conventional delayed-enhancement method. High correlation between both representations shows promise of FA in assessment of viability without negative effects of contrast agents.

An Extended Graphical Model for Analysis of Dynamic Contrast-Enhanced MRI
Huijun Chen¹, Feiyu Li¹, Xihai Zhao¹, Chun Yuan¹, William S. Kerwin^1
1Department of Radiology, University of Washington, Seattle, WA, United States

Kinetic modeling of DCE-MRI permits the measurement of physiological parameters, such as K^trans. The modified Kety/Tofts model may lead to fit failures when the data acquisition period is too short. The estimates of the Patlak model can be highly inaccurate due to the neglecting of contrast agent reflux. In this investigation, an extended graphical model is proposed. In the tests of simulation data and in vivo data of carotid artery, the proposed extended graphical model was shown to address the bias inherent in the Patlak model and produce more stable estimates than the modified Kety/Tofts model for short duration experiments.

Improved T2* Estimation Technique in Human Carotid Arteries
Travis Patrick Sharkey-Toppen¹, Bradley Dean Clymer¹, Andrei Maiseyeu¹, Tam Tran¹, Georgeta Mihai¹, Subha V. Raman^1
1The Ohio State University, Columbus, OH, United States

Atherosclerosis is one of the leading causes of death worldwide. It has been shown that iron may play a significant role in the development of plaque. Quantification of iron via T2* is complicated in small vessels such as the carotids due to their limited size, motion and flow artifacts. Evaluation of a new T2* estimation technique which utilizes WLSE and outlier detection is shown to lower the effect of noise and increase reproducibility in small vessels.

Three-Dimensional Prolate Spheroidal Extrapolation for Sparse DTI of the In-Vivo Heart
Nicolas Toussaint¹, Christian Stoeck², Maxime Sermesant^1,3, Sebastian Kozerke^1,2, Philip Batchelor^1
1Imaging Sciences, King's College London, London, United Kingdom; ²ETH Zurich, Zurich, Switzerland; ³Asclepios Research Group, INRIA, Sophia Antipolis, France

We propose to extrapolate sparsely distributed cardiac DTI using prolate spheroid coordinate system. For this, a segmented shape of the left ventricle is mapped to the closest truncated prolate spheroid using a non-linear diffeomorphic registration algorithm. Thereby, the tensor components and spatial positions can be expressed in prolate spheroid coordinates. After extrapolation, dense tensors are mapped back using the symmetric transformation. Comparison with the classic Cartesian extrapolation shows better consistency of the tensor field at unknown positions. It is demonstrated that this shape-based extrapolation method gives robust estimation of the in-vivo fibre architecture of the left ventricle.  

Fourier Analysis of STimulated Echoes (FAST) for Quantitative Analysis of Left Ventricular Torsion
Meral Reyhan¹, Daniel B. Ennis¹, Yutaka Natsuaki^2
1Radiological Sciences, University of California, Los Angeles, CA, United States; ²Siemens Medical Solutions USA, Inc., Los Angeles, CA, United States

Left ventricular (LV) torsion is an important measure of LV performance.  This study validates a novel quantitative method (Fourier Analysis of STimulated echoes - FAST) for the rapid quantification of LV torsion by comparison to a “gold standard” method (FindTags) and finds no statistical difference between the methods in six canine studies.  The intraobserver coefficient of variation (CV) for each observer was 4.2% and 2.3%. The interobserver CV was 8.4% and 5.4%.  FAST analysis of LV torsion in six healthy-subjects demonstrates quantitation of systolic torsion and early untwisting.  FAST is a highly reproducible and rapid (<3 minutes-per-study) quantitative method.

Varied Sampling Patterns in Modified Look-Locker with Saturation Recovery for Flexible Cardiac T1 Mapping
Ting Song^1,2, Vincent B. Ho^2,3, Glenn Slavin¹, Maureen N. Hood^2,3, Jeffrey A. Stainsby^4
1GE Healthcare Applied Science Laboratory, Bethesda, MD, United States; ²Radiology, Uniformed Services University of the Health Sciences, Bethesda, MD, United States; ³Radiology, National Navy Medical Center, Bethesda, MD, United States; ⁴GE Healthcare Applied Science Laboratory, Toronto, ON, Canada

A cardiac T1 mapping sequence using a modified Look-Locker with saturation recovery acquisition provides increased flexibility with respect to sampling of the signal recovery curve over more traditional inversion recovery T1 mapping methods. In this work we explore different sampling patterns on phantoms and human subjects. A sampling scheme requiring half the data samples and thus half the breath hold time is compared to previous methods. An SNR sensitivity analysis was performed to confirm the accuracy of the reduced data sampling method at clinically relevant SNR and tissue T1 values.

Fully Automated Generation of Arteriogram and Venogram Using Correlation and Pooled Covariance Matrix Analysis
Jiang Du¹, Afshin Karami¹, Yijing Wu², Frank Korosec², Thomas Grist², Charles Mistretta^2
1Radiology, University of California, San Diego, CA, United States; ²Medical Physics and Radiology, University of Wisconsin, Madison, WI, United States

Time-resolved CE--MRA provides contrast dynamics in the vasculature, which can be further used to separate arteries from veins. However, most of the segmentation algorithms require operator intervention. Furthermore, the contrast dynamics pattern may vary significantly within a large coronal imaging FOV due to delayed or asymmetric filling, or slow blood flow in the tortuous vessels. Correlation with single arterial and/or venous reference curves may result in misclassification. Here we present a fully automated region-specific segmentation algorithm for effective separation of arteries from veins based on cross correlation and pooled covariance matrix analysis.

Stent Visualization by Susceptibility Field Mapping Using the Original Resolution
Gopal Varma¹, Rachel Clough¹, Julien Senegas², Hannes Dahnke², Stephen Keevil^1,3, Tobias Schaeffter^1
1Imaging Sciences, King's College London, London, United Kingdom; ²Philips Research Europe, Hamburg, Germany; ³Medical Physics, Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom

Visualization of stent-grafts allows guidance and deployment to be assessed. Detection by negative contrast can be confused with other sources of hypo-intensity. A modified version for SGM is presented for positive visualization without compromise in resolution. This and its application by post-processing allows the information from both contrasts to be used without registration.

Heart-Within-Heart Dynamic Systems Implicit in Myocardial Fiber Architecture Revealed by Diffusion Tensor Tractography
Kuan-Liang Liu¹, Hsi-Yu Yu², V. J. Wedeen³, Wen-Yih Isaac Tseng^1,4
1Center for Optoelectronic Biomedicine, National Taiwan University, Taipei, Taiwan; ²Departments of Surgery, National Taiwan University Hospital, Taiwan; ³Department of Radiology, MGH Martinos Center for Biomedical Imaging, Harvard Medical School, Charlestown, MA, United States; ⁴Department of Medical Imaging, National Taiwan University Hospital, Taiwan

It is long known that the myocardial architecture has its functional significance. However, up to now there are no models that can fully explain the relationship between myocardial fiber structure and the mechanism of cardiac motion. In this study, we proposed using diffusion tensor imaging and fiber tracking technique to perform virtual dissection of the myocardial fiber architecture. We found that the LV myocardial fibers can be classified into two systems; the inner heart system corresponds to the motion of torsion and longitudinal shortening and the outer heart system corresponds to radial contraction of the LV wall.