Young Investigator Award Presentations
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Monday 7 May 2012
Plenary Hall  14:15 - 16:15 Moderators: John A. Detre, Karla L. Miller

14:15 0066.   
Arterial Input Function for Bolus Tracking Perfusion Imaging in the Brain
Elias Kellner1, Irina Mader2, Daniel Nico Splitthoff1, Marco Reisert1, Katharina Förster3, Thao Nguyen-Thanh2, Peter Gall1, and Valerij G. Kiselev1
1Department of Radiology, Medical Physics, University Medical Center Freiburg, D-79106 Freiburg, Germany, 2Section of Neuroradiology, Neurocenter of the Freiburg University Hospital, D-79106 Freiburg, Germany, 3Department of Cardiovascular Surgery, Albert-Ludwigs-University Freiburg, D-79106 Freiburg, Germany

Dynamic susceptibility contrast MRI is a well-known method for determination of perfusion parameters in the brain. The major challenge of the method is to measure the contrast inflow into the brain, commonly, the arterial input function (AIF). The measurement of the AIF is subject to a number of problems such as signal void in blood, nonlinear dependence on contrast agent concentration and partial volume effects. In this study, those problems are solved with an extension of a conventional perfusion pulse sequence. Results obtained in an animal model reproduce known values of the cardiac output and the cerebral blood volume.

14:35 0067.   Nonlinear Formulation of the Magnetic Field to Source Relationship for Robust Quantitative Susceptibility Mapping
Tian Liu1, Cynthia Wisnieff2,3, Min Lou4, Weiwei Chen5, Pascal Spincemaille3, and Yi Wang2,3
1MedImageMetric LLC, New York, NY, United States, 2Biomedical Engineering, Cornell University, Ithaca, NY, United States, 3Radiology, Weill Cornell Medical College, New York, NY, United States, 4Neurology, The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China, 5Radiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science& Technology (HUST), Wuhan, Hubei, China

Quantitative Susceptibility Mapping is becoming an increasingly active area of scientific and clinical investigations. In practical applications, there are sources of errors for QSM including noise, phase unwrapping failures and signal model inaccuracy. To improve the robustness of QSM quality, we propose a nonlinear data fitting for field map estimation and dipole inversion to reduce noise and phase unwrapping failures, and a method for model error reduction through iterative tuning. Compared to the previous linear QSM method, this nonlinear QSM method reduced checkerboard pattern in high susceptibility regions in healthy subjects and markedly reduced artifacts in patients with intracerebral hemorrhages.

14:55 0068.   
Chemical Shift Induced Phase Errors in Phase Contrast MRI
Matthew J. Middione1,2, and Daniel B. Ennis1,2
1Department of Radiological Sciences, Diagnostic Cardiovascular Imaging Section, University of California, Los Angeles, CA, United States, 2Biomedical Physics Interdepartmental Program, University of California, Los Angeles, CA, United States

Phase contrast MRI (PC-MRI) is subject to numerous sources of error, which decrease both quantitative accuracy and clinical confidence in the reported measures. Perivascular fat surrounds most vessels and can chemically shift across the vessel wall into the lumen, thereby superposing the complex off-resonant fat signal onto the complex signal in a pixel containing flowing blood. This phase error can lead to a clinically significant over- or underestimation of net forward flow (10-20mL). A judicious choice of bandwidth and TE can reduce the chemical shift induced phase errors in PC-MRI net forward flow measurements to clinically insignificant levels (<5mL).

15:15 0069.   
Spatially Resolved Extended Phase Graphs: modeling and design of multi-pulse sequences with Parallel Transmission
Shaihan J Malik1, and Joseph V Hajnal1
1Robert Steiner MRI Unit, Imaging Sciences Department, MRC Clinical Sciences Centre, Hammersmith Hospital, Imperial College London, London, London, United Kingdom

RF inhomogeneity correction using parallel transmission usually focuses on optimising RF field uniformity. Although improving field homogeneity generally improves images, most imaging sequences employ rapid successions of RF pulses, making the received signals depend on the combined history of many pulses interspersed with periods of relaxation. Independent modulation of separate pulses provides additional degrees of freedom for manipulation of resulting signal. Using a spatially resolved extended phase graph (SREPG) signal model, RF inputs may be optimised to produce uniform signals from non-uniform fields. Improved image homogeneity with more uniform contrast is demonstrated on 3D TSE brain imaging at 3T.

15:35 0070.   
In vivo O-Space imaging with a dedicated 12 cm Z2 insert coil on a human 3T scanner using phase map calibration
Jason Stockmann1, Gigi Galiana2, Leo Tam1, Christoph Juchem2, Terence Nixon2, and Robert Todd Constable1,2
1Biomedical Engineering, Yale University, New Haven, CT, United States, 2Diagnostic Radiology, Yale University, New Haven, CT, United States

We present the first accelerated in vivo "O-Space" images acquired using a quadratic gradient insert coil in combination with conventional linear gradients. We achieve a highly accurate calibration by using phase encoding to map the spin phase in each voxel at every readout point of the O-Space pulse sequence, accounting for effects of field strength, timing, concomitant fields, and eddy currents. O-Space images compare favorably to under-sampled radial and Cartesian images at high acceleration factors using only 8 receive coils. This work paves the way for more in-depth future investigation of projection imaging with nonlinear encoding fields.

15:55 0071.   
A Kinetic Model for Vessel-Encoded Dynamic Angiography with Arterial Spin Labeling
Thomas W Okell1, Michael A Chappell1,2, Ursula G Schulz3, and Peter Jezzard1
1FMRIB Centre, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2Institute of Biomedical Engineering, Department of Engineering, University of Oxford, Oxford, Oxfordshire, United Kingdom, 3Stroke Prevention Research Unit, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, Oxfordshire, United Kingdom

Vessel-encoded dynamic angiography with arterial spin labeling is able to produce artery-specific images qualitatively showing the blood flow patterns, vessel morphology and hemodynamics. Here we develop a kinetic model to describe the signal in such acquisitions, allowing the generation of parameter maps relating to blood volume, arrival time and dispersion, which may provide useful biomarkers of disease. These parameters are also used to generate intuitive inflow images and calculate the relative blood volume flow rates in downstream vessels from each feeding artery. Results from application of these methods in healthy volunteers and a patient with Moyamoya disease are shown.