Improving DSC-MRI by Orientation-Corrected Phase-Based AIF and VOF
Matus Straka¹, Rexford D. Newbould², Milos Sramek³, Gregory W. Albers⁴, Roland Bammer^1
1Radiology, Stanford University, Stanford, CA, United States; ²Clinical Imaging Centre, GlaxoSmithKline, London, United Kingdom; ³Commision for Scientific Visualization, Austrian Academy Of Sciences, Vienna, Austria; ⁴Stroke Center, Stanford University Medical Center, Stanford, CA, United States

Quantitative perfusion measurements require accurate measurements of tracer concentration. Magnitude T2*-based data suffer from various artifacts and non-linearities and make quantification of (mainly vascular) tracer concentration difficult. Concentration can be derived from change in resonante frequency (phase of MR signal), however this effect depends on orientation of given vessel versus main magnetic field. Image-based filtering to enhance cylindrical structures is used to estimate vessel orientation from DSC-MRI data. This information is used to correct the phase information and improve quantification of Gd concentration in large vessels.

Brain Perfusion with MRI: Arterial Input Function Localization with the Support of MR Angiography
Bora Buyuksarac¹, Mehmed Ozkan^1
1Bogazici University, Istanbul, Turkey

In perfusion weighted images, the anatomic locations of the arteries are not clearly visible. The conventional arterial input function selection technique is to locate a region on a perfusion image that is supposed to include an artery and select the pixels of which time curves meet the criteria of steepness, narrowness and high signal intensity change. In this study, we alternatively employ MR angiography (MRA) images for more accurate results in localizing the arteries. With this method we achieve automated multiple AIF selection, through which regional CBF images on various brain slices are calculated.

New Criterion for Automatic AIF Selection in DSC Perfusion MRI to Exclude Partial Volume Effects
Egbert J. W. Bleeker¹, Matthias J. P. van Osch¹, Alan Connelly^2,3, Mark A. van Buchem¹, Andrew G. Webb¹, Fernando Calamante^2,3
1C.J.Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands; ²Brain Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, Australia; ³Department of Medicine, University of Melbourne, Melbourne, Australia

The current criteria for AIF selection algorithms determine “correct” measurements based on the shape of the first passage. However, this shape can be altered by partial volume effects, which often occur in AIF measurements due to the relatively low spatial resolution. A new criterion is proposed, based on tracer kinetic theory, that uses the additional information of the steady state to detect partial volume effects in the AIF measurement. This study shows that the proposed criterion should be a valuable addition to the current selection criteria.

Quantitative Cerebral Perfusion with SCALE-PWI: Accelerated Image Acquisition and Optimized Image Reconstruction
Jessy J. Mouannes¹, Wanyong Shin², Saurabh Shah³, Anindya Sen⁴, Sameer Maheshwari¹, Timothy J. Carroll^1,4
1Biomedical Engineering, Northwestern University, Chicago, IL, United States; ²National Institute on Drug Abuse, National Institute of Health, Baltimore, MD, United States; ³Siemens Medical Solutions USA, Chicago, IL, United States; ⁴Radiology, Northwestern University, Chicago, IL, United States

The multi-scan Bookend technique allows accurate, reliable and reproducible quantitative cerebreal perfusion measurements. An accelerated and simplified version of the Bookend technique protocol has been achieved through a Self-CALibrated Epi Perfusion Weighted Imaging (SCALE-PWI) MRI pulse sequence, with scan time under 2 minutes and allowing inline reconstruction of quantitative images of cerebral perfusion.  A study of two different delay times between consecutive modules of SCALE-PWI and a water correction factor (WCF) parameterization for SCALE-PWI are presented at 1.5T. The results show that a fast imaging protocol for SCALE-PWI (with zero delay) with appropriate WCF parameterization provide accurate quantitative cerebral perfusion.

Measurement of Cerebral Blood Flow and Cerebral Blood Volume in Humans Using Washout of Hyperoxic Contrast
David Thomas Pilkinton¹, Santosh Gaddam¹, Mark A. Elliott¹, Ravinder Reddy^1
1Center for Magnetic Resonance and Optical Imaging, University of Pennsylvania, Philadelphia, PA, United States

It has long been thought that hyperoxia alters the hemodynamics of the brain substantially, confounded attempts to measure hemodynamic quantities with hyperoxic contrast.  However, recent studies have shown that cerebral blood flow (CBF) experiences only a small (<4%) reduction upon breathing low to moderate oxygen concentrations (FiO2≤0.5). Since hyperoxic contrast exhibits fast washout times, accurate measurements of dynamic parameters are feasible.  We have shown here that that accurate measurements of CBV and CBF can be made dynamically during the washout of hyperoxic contrast using indicator-dilution theory in a manner akin to traditional dynamic susceptibility contrast (DSC) measurements.

On the Role of Tissue–blood Exchange on the Relaxation Effect of Paramagnetic Blood Tracers
José Rufino Solera Ureña¹, Salvador Olmos Gassó¹, Valerij G. Kiselev^2
1Aragon Institute of Engineering Research, Universidad de Zaragoza, Zaragoza, Spain; ²Dept. of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany

The signal attenuation observed in DSC–MRI measurements is considered largely to obey to susceptibility-induced magnetic inhomogeneities at the mesoscopic scale. Another mesoscopic process contributing to increased spin dephasing is the diffusion of tissue water carrying a transverse magnetisation M into the blood pool, where it then experiences faster relaxation due to the presence of paramagnetic contrast agent. To quantify this effect, an effective extravascular dephased volume is defined. Analytical expressions are given for various exchange regimes and numerical estimates are compared with the vascular volume. Results indicate that in the brain the exchange of tissue magnetisation across the blood–brain barrier is permeability limited and does not contribute significantly to the signal dephasing. However, the contribution of magnetisation exchange may be important in organs with increased capillary permeability and/or blood volume. The method  is applicable to other problems in quantitative perfusion MRI.

PET Validation of Vascular-Space-Occupancy CBV Measurement
Jinsoo Uh¹, Ai-Ling Lin², Kihak Lee², Peter Fox², Hanzhang Lu^1
1Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States; ²Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, United States

This study validates the use of VASO-MRI for quantitative measurement of cerebral blood volume in unit of ml blood in 100 ml brain. We measured CBV values using PET and VASO-MRI on the same subjects and compared them. The results showed that VASO-MRI provides quantitative and accurate estimations of CBV values in the human brain. Our data also demonstrated that VASO CBV has a higher SNR compared to the PET technique in addition to providing a higher spatial resolution.

Quantitative Assessment of Perfusion and Permeability in Multiple Sclerosis: Feasibility and Initial Results
Michael Ingrisch¹, Steven Sourbron¹, Dominik Morhard, Lisa-Ann Gerdes², Tania Kümpfel², Reinhard Hohlfeld², Maximilian F. Reiser, Christian Glaser
¹Josef Lissner Laboratory for Biomedical Imaging, Institute of Clinical Radiology, Ludwig Maximilian University, Munich, Germany; ²Institute for Clinical Neuroimmunology, Ludwig Maximilian University, Munich, Germany

We evaluate the feasibility of a 3D DCE-MRI measurement for the absolute quantification of perfusion and permeability in Multiple Sclerosis and present initial results. 19 patients were examined, perfusion and permeability were quantified with 2-compartment models in white matter, non-enhancing(NE) and contrast-enhancing(CE) lesions. The results show clear separation of WM and CE lesions in the permeability estimates; WM perfusion was lower than standard values from literature. The parameter variation in NE- and CE-lesions was relatively large, suggesting a potential for lesion characterization and monitoring of the effects of disease-modifiying drugs.

Steady State Effects on Cerebral Blood Flow Measurements Using Dynamic Contrast-Enhanced Perfusion MRI: A Simulation Study
Adam Espe Hansen¹, Henrik Pedersen¹, Henrik BW Larsson^1
1Functional Imaging Unit, Glostrup Hospital, University of Copenhagen, Glostrup, Denmark

Dynamic contrast enhanced (DCE) perfusion MRI of the passage of a Gd bolus requires rapid imaging, which will introduce steady state effects. We simulate the time development of the longitudinal magnetization during a typical R₁ time course and evaluate the influence of steady state effects on the estimation of cerebral blood flow (CBF). We find that steady state effects can seriously affect CBF estimates if the saturation prepulse is not exact. The CBF bias can be minimized to a few percent if a large alfa flip angle of the order of 30 degrees is used.

Towards More Accurate Modeling of DCE Data: Development of a Multi-Compartment Phantom
Jeff R. Anderson¹, Joseph J H Ackerman¹, Joel R. Garbow^1
1Washington University in St. Louis, St. Louis, MO, United States

Dynamic contrast enhanced (DCE) MRI is a powerful tool for the imaging of cancer in vivo. However, debate still remains in the literature about which DCE signal model(s) best reflect(s) the image time-course data. An in vitro phantom, based on semi-permeable hollow fibers, has been constructed as a novel platform to assess the quantitative limits of DCE-MRI parameter estimation. Time-of-flight effects allow the intra-lumen signal to be suppressed in the presence of lumen flow and, thus, the kinetic characteristics defining contrast-agent diffusion through the fiber walls into the extra-lumen space to be quantitatively assessed.