Flow Quantification

Monday 22 April 2013

Alex J. Barker¹, Krishna C. Bandi², Julio Garcia¹, Pim van Ooij¹, Patrick McCarthy², James C. Carr¹, S Chris Malaisrie², and Michael Markl^1
1Radiology, Northwestern University, Chicago, IL, United States, ²Cardiac Surgery, Northwestern University, Chicago, IL, United States

In this study, the measurement of viscous energy loss, a parameter which is directly responsible for increased cardiac afterload and is independent of pressure recovery effects, was used to quantify LV loading in the presence of aortic valve disease (AVD). A theoretical basis for the technique is presented and applied in-vivo using 4D flow MRI in a range of healthy, dilated aorta, and aortic stenosis (AS) subjects (n=26). Abnormal flow features, combined with systolic flow jets and flow-jet/wall impingement, resulted in statistically elevated energy loss for dilated (0.08±0.02W, p=0.011) and AS patients (0.81±0.42W, p<0.001), compared to healthy volunteers (0.05±0.02W).

Oliver Wieben^1,2, Alejandro Roldán-Alzate², Scott B. Reeder^1,2, Mark L. Schiebler², Scott K. Nagle², Charles W. Acher³, Ben Ray Landgraf², Thomas M. Grist², and Christopher J. Francois^2
1Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, ²Radiology, University of Wisconsin-Madison, Madison, WI, United States, ³Surgery, University of Wisconsin-Madison, Madison, WI, United States

This pilot study investigates the use of 4D flow MRI to improve diagnosis of mesenteric ischemia by providing simultaneous anatomical depiction and functional assessment of the hemodynamics before and after a meal challenge. MR Flow data from a meal challenge are presented for eight patients suspected of mesenteric ischemia, demonstrating high potential to improve diagnostics and therapeutic decision making in this challenging diagnosis.

Julio Garcia¹, Romain Capoulade², Lyes Kadem³, Eric Larose², and Philippe Pibarot^2
1Radiology, Northwestern University, Chicago, Illinois, United States, ²Laval University, Quebec, Quebec, Canada, ³Concordia University, Montreal, Quebec, Canada

Transvalvular mean pressure gradient (MPG) measured by CMR often underestimates echo-Doppler MPG. This underestimation might be due to physical factors as flow turbulence generated downstream the severe AS, local signal loss, background noise and phase wrap. However fluid dynamic parameters may play also a significant role in the MPG measurement by CMR. The aims of this study were to identify the fluid dynamic factors associated with MPG underestimation by CMR and to investigate the association of those factors in the AS severity assessment by CMR.

Andrew L. Wentland^1,2, Thomas M. Grist^2,3, Dhanansayan Shanmuganayagam⁴, Christian G. Krueger⁴, Patrick E. McBride⁵, Jennifer J. Meudt⁴, Jess D. Reed⁴, and Oliver Wieben^1,2
1Medical Physics, University of Wisconsin School of Medicine & Public Health, Madison, WI, United States, ²Radiology, University of Wisconsin School of Medicine & Public Health, Madison, WI, United States, ³Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, ⁴Animal Sciences, University of Wisconsin, Madison, WI, United States, ⁵Medicine, University of Wisconsin School of Medicine & Public Health, Madison, WI, United States

The purpose of this study was to evaluate pulse wave velocity (PWV) measurements derived from 2D and 4D phase contrast MRI in swine with hypercholesterolemia and to compare these measurements to those derived from gold standard pressure probes. Bland-Altman analysis revealed relatively small differences between the MR and pressure probe PWV values; there was less variability with the 4D PWV measurements than with the 2D techniques. Correlation to pressure probe measurements was stronger with the 4D technique than with the 2D techniques. The 4D acquisition provides a promising means of computing PWV in a swine model of atherosclerosis.

Ning Jin¹, Rizwan Ahmad², Yu Ding², Sven Zuehlsdorff³, and Orlando P. Simonetti^2,4
1Siemens Healthcare, Columbus, OH, United States, ²Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH, United States, ³Siemens Healthcare, Chicago, IL, United States, ⁴Department of Department of Internal Medicine, The Ohio State University, Columbus, OH, United States

A novel echo-planar (EPI) implementation of balanced four-point velocity encoded PC-MRI for rapid, breath-hold acquisition of three-directional velocity data with high temporal resolution is presented. A direct inversion with regularized least square estimation of velocities from the acquired phase data is used to increase temporal resolution by a factor of four. The combined approach enables simultaneous measurements of vx, vy, and vz with an effective temporal resolution of 14.5 ms within a single breath-hold.

Mo Kadbi¹, Melanie S. Traughber², Peter Martin², and Amir A. Amini^1
1Elect. and Comp. Eng., University of Louisville, Louisville, KY, United States, ²Philips healthcare, Highland Heights, OH, United States

4-D flow MRI has been recently investigated in several studies for quantitative flow assessment and visualization of complex flow pattern. Conventional 4-D PC MRI is not promising technique in the presence atherosclerotic disease and vascular stenosis due to intravoxel dephasing secondary to disturbed blood flow, and turbulence distal to narrowing often resulting in flow-related artifacts. Ultra-short TE (UTE) PC MRI revealed a shorter TE and improvement in flow quantification in disturbed and turbulent blood flow in through-plane direction . To take advantage of 4-D flow MRI as well as short TE, UTE technique was combined with 4D flow imaging and a 4-D UTE PC MRI technique was investigated. The fusibility of this technique for comprehensive flow assessment in healthy carotid artery compared to conventional 4-D PC MRI was studied.

Vinicius de Carvalho Rispoli^1,2 and Joao L. A. Carvalho^1
1Department of Electrical Engineering, University of Brasília, Brasília, DF, Brazil, ²UnB-Gama Faculty, University of Brasília, Gama, DF, Brazil

Fourier velocity encoding (FVE) provides considerably higher SNR than phase contrast, and is robust to partial-volume effects. FVE typically presents low spatial resolution, due to scan-time restrictions associated with its higher dimensionality. FVE is capable of providing the velocity distribution associated with a large voxel, but does not directly provides a velocity map. We propose a method for deriving high spatial resolution velocity maps from low-resolution FVE data. Experiments using numerical phantoms, as well as simulated spiral FVE data derived from real phase contrast data, show that it is possible to obtain reasonably accurate velocities maps from low-resolution FVE distributions.

Julia Busch¹, Signe Johanna Vannesjo¹, Christoph Barmet^1,2, Klaas P. Pruessmann¹, and Sebastian Kozerke^1,3
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, ²Skope Magnetic Resonance Technologies, Zurich, Switzerland, ³Division of Imaging Sciences and Biomedical Engineering, King’s College London, London, United Kingdom

Background phase errors of various spatial and temporal orders limit the accuracy of phase-contrast magnetic resonance imaging. Current calibration techniques can compensate for them almost completely; however, they require the MR system to be temporally stable. In the present work we analyze the stability of background phase errors under thermal changes of the gradient system as it may occur for scans of long duration and high duty-cycle. Measurement of the gradient impulse response function shows a shift in frequency of the oscillatory field fluctuations with increasing temperature which results in a change of 0th and 1st order field offsets.

Michael Loecher¹, Oliver Wieben^1,2, and Kevin M. Johnson^1
1Medical Physics, University of Wisconsin Madison, Madison, Wisconsin, United States, ²Radiology, University of Wisconsin Madison, Madison, Wisconsin, United States

This study applies a single-step Laplacian based unwrapping algorithm to 4D-Flow MRI. The Laplacian operation is extended to all 4 dimensions to solve for a continuous phase field in space and time. Digital flow phantom experiments show the improved performance for varying SNR and VENC settings, and in vivo measurement with significant wrapping are shown to be successfully unwrapped.