Coregistration of Wall Shear Stress and Plaque Distribution Within the Thoracic Aorta of Acute Stroke Patients
Michael Markl¹, Stephanie Brendecke², Jan Simon¹, Alex Frydrychowicz³, Andreas Harloff^2
1Diagnostic Radiology, Medical Physics, University Hospital, Freiburg, Germany; ²Neurology, University Hospital, Freiburg, Germany; ³Radiology, University of Wisconsin, Madison, United States

Flow-sensitive 4D-MRI (3D morphology and 3-directional blood flow) and segmental wall shear stress analysis were employed in 94 patients with aortic atherosclerosis. A one-to-one comparison of wall parameter distribution with plaque location was performed in a large number of complex aortic plaques. Critical wall parameters such as low wall shear stress and high oscillatory shear index were concentrated at the inner curvature of the aorta and near the outlet of the supra-aortic arteries. For most complex plaques a consistent location of critical wall parameters in wall segments adjacent to the atheroma suggested a close correlation of hemodynamics and advanced atherosclerosis.

Analysis of Right Atrial and Ventricular Flow Patterns with Whole Heart 4D Flow MRI – Comparison of Tetralogy of Fallot with Normal Volunteers
Christopher J. François¹, Shardha Srinivasan², Benjamin R. Landgraf¹, Alex Frydrychowicz¹, Scott B. Reeder^1,3, Mark L. Schiebler¹, Oliver Wieben^1,3
1Radiology, University of Wisconsin, Madison, WI, United States; ²Pediatrics, University of Wisconsin, Madison, WI, United States; ³Medical Physics, University of Wisconsin, Madison, WI, United States

An appropriate understanding of cardiac function requires analysis of flow patterns through the heart. This is particularly true in congenital heart disease prior to and following repair, where reconstruction of a normally functioning heart would be desirable. This work describes the analysis of flow patterns in the right heart in normal volunteers and patients with Tetralogy of Fallot using whole heart 4D flow MRI.

Simultaneous Quantification of Blood Velocity and Oxygenation in Femoral Artery and Vein in Response to Cuff-Induced Ischemia
Michael C. Langham¹, Jeremy Magland¹, Felix W. Wehrli^1
1Radiology, University of Pennsylvania, Philadelphia, PA, United States

Quantifying reactive hyperemia in the lower extremities is a common approach for assessing vascular dysfunction associated with peripheral arterial disease (PAD). Often assessment is limited to measuring a single physiologic parameter such as velocity, flow-mediated dilatation and blood oxygenation. As a first step toward the development of an integrated MRI examination of PAD we have combined velocity quantification technique with a field mapping pulse sequence allowing simultaneous time-course mapping of blood velocity and oxygenation in femoral artery and vein during cuff-induced hyperemia. The results of blood velocity and oxygenation quantification agree with those found in the literature.

5-Point, Ultra-Short TE, 3D Radial Phase Contrast: Improved Characterization of Complex and Turbulent Flow
Kevin M . Johnson^1
1Medical Physics, University of Wisconsin - Madison, Madison, WI, United States

The accuracy of PC MR is deteriorated by flow features common to pathology such as acceleration, unstable flow, and turbulence. Recently, ultra short TE 2D radial sequences have been shown to provide more reliable through plane flow measurements than standard PC.  Meanwhile, investigators have utilized conventional 3D PC sequences for the measurement of turbulence kinetic energy using signal losses.  In this work, we investigate a synergistic combination of ultra-short TE 3D radial trajectories and a 5-point velocity encoding scheme for improvements in both the velocity measurement accuracy and estimation of intra-voxel standard deviations utilized for turbulence mapping.

Hadamard-Transform K-T PCA for Cine 3D Velocity Vector Field Mapping of Carotid Flow
Verena Knobloch¹, Daniel Giese¹, Peter Boesiger¹, Sebastian Kozerke^1
1Institute for Biomedical Engineering, Swiss Federal Institute of Technology and University Zurich, Zurich, Switzerland

It has been shown recently that k-t PCA permits high acceleration without compromising the accuracy of single directional flow quantification. In this work 3D velocity fields are measured in a phantom and an in-vivo case and reconstructed with different acceleration factors. Pathline tracking is possible up to an acceleration factor of 10.

Metric Optimized Gating for Fetal Cardiac MR Imaging
Michael Shelton Jansz^1,2, Mike Seed³, Joshua F. van Amerom^1,2, Shi Joon Yoo^3,4, Christopher K. Macgowan^1,2
1Medical Biophysics, University of Toronto and Hospital for Sick Children, Toronto, Ontario, Canada; ²Medical Imaging, University of Toronto and Hospital for Sick Children, Toronto, Ontario, Canada; ³Pediatric Cardiology, University of Toronto and Hospital for Sick Children, Toronto, Ontario, Canada; ⁴Dignostic Imaging, University of Toronto and Hospital for Sick Children, Toronto, Ontario, Canada

Phase-contrast MRI of pulsatile flow typically requires cardiac gating; however, a gating signal is not necessarily available in utero for fetal cardiac imaging.  We propose a new technique for reconstructing ungated data where the gating is determined retrospectively by optimizing an image metric.  Simulations and in vivo data are presented to demonstrate the feasibility of this technique.

Objective Characterization of Disease Severity by Determination of Blood Flow Reserve Capacity of the Popliteal Artery in Intermittent Claudication
Bastiaan Versluis¹, Marjolein HG Dremmen¹, Patty J. Nelemans², Joachim E. Wildberger¹, Tim Leiner¹, Walter H. Backes^1
1Radiology, Maastricht Universitary Medical Centre, Maastricht, Netherlands; ²Epidemiology, Maastricht Universitary Medical Centre, Maastricht, Netherlands

Objective characterization of peripheral arterial disease (PAD) severity remains difficult purely on the basis of morphological assessement. We describe a method to determine rest flow and blood flow reserve capacity (BFRC) of the popliteal artery, using serial velocity encoded 2D MR cine PCA flow measurements. Using this method, we found a strong reduction in rest flow, maximum flow and BFRC in 10 patients with intermittent claudication compared to 10 healthy subjects. This method can potentially be used to supplement MR angiography to objectively characterize PAD disease severity and to monitor therapy efficacy in intermittent claudication.

Analysis of Complex Flow Patterns with Acceleration-Encoded MRI
Felix Staehle¹, Simon Bauer¹, Bernd André Jung¹, Jürgen Hennig¹, Michael Markl^1
1Department of Diagnostic Radiology, University Hospital Freiburg, Freiburg, Germany

The phase contrast principle (PC) can be employed to measure flow acceleration by using acceleration sensitive encoding gradients. The aim of this study was to evaluate a newly developed gradient optimized acceleration-sensitive PC-MRI technique with full three-directional acceleration encoding of aortic blood flow. Results were compared to standard velocity encoded phase contrast MRI. In addition, the value of acceleration induced intravoxel dephasing as a new image contrast providing information about complex and vortical flow was investigated.

Novel Hybrid Real-Time Phase-Contrast Sequence
Jennifer Anne Steeden^1,2, David Atkinson¹, Andrew M. Taylor², Vivek Muthurangu^2
1Medical Physics, University College London, London, United Kingdom; ²Centre for Cardiovascular MR, UCL Institute of Child Health, London, United Kingdom

Real-time phase contrast (PC) imaging has a low temporal resolution because interleaved flow-encoded and compensated readouts must be acquired. We have developed a hybrid real-time PC sequence that acquires real-time flow-encoded and flow-compensated readouts in alternating blocks. The encoded data is subsequently matched to the compensated data, allowing the temporal resolution to be effectively doubled. This technique was demonstrated in 10 volunteers to adequately match the flow-compensated data to the flow-encoded data. It was also shown to accurately measure stroke volumes, with a good correlation against a reference gated sequence and an in-house real-time interleaved flow sequence.

Analysis and Correction of Background Velocity Offsets in Cine Phase-Contrast Imaging Using Magnetic Field Monitoring
Daniel Giese^1,2, Maximilian Haeberlin¹, Christoph Barmet¹, Tobias Schaeffter², Klaas Paul Pruessmann¹, Sebastian Kozerke^1,2
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; ²Division of Imaging Sciences, King's College London, London, United Kingdom

The sensitivity of phase contrast MRI to magnetic field gradient imperfections has long been recognized and a number of image-based approaches exist to partially correct for background velocity offsets. Image-based velocity offset correction assumes a sufficient number of static image pixels and often only phase offsets with 0th  and 1st order in space can be accounted for. In this work, a 16-channel magnetic field camera is employed to analyze and correct background velocity offsets in cine phase-contrast velocity imaging. It is demonstrated that phase offsets exhibit primarily constant and linear terms in space but do considerably vary in magnitude over time in triggered cine sequences necessitating heart-phase dependent correction.