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Thursday 10 May 2012
Room 212-213  16:00 - 18:00 Moderators: Jelena Bock, Christopher Jean-Pierre Francois

16:00 0664.   
Noninvasive estimation of pulmonary vascular resistance with 4D flow-sensitive MRI in a canine model of acute pulmonary arterial hypertension
Alejandro Roldan-Alzate1, Alex Frydrychowicz2, Leif Jensen1, Scott K Nagle1, Heidi Kellihan3, Naomi Chesler4, Oliver Wieben1,5, and Christopher J François1
1Radiology, University of Wisconsin, Madison, WI, United States, 2Radiology, Universitatsklinikum Schleswig-Holstein, Lubeck, Germany, 3Veterinary Medicine, University of Wisconsin, Madison, WI, United States, 4Biomedical Engineering, University of Wisconsin, Madison, WI, United States, 5Medical Physics, University of Wisconsin, Madison, WI, United States

Pulmonary vascular resistance (PVR) is a hemodynamic parameter that is used to assess disease severity and to guide the management of patients with a variety of cardiovascular and pulmonary conditions. 4D flow-sensitive MRI is increasingly being used for hemodynamic analyses of cardiovascular diseases, including pulmonary arterial hypertension. PC VIPR is a time-efficient 4D flow-sensitive MRI technique, using radial undersampling, to obtain high spatial resolution data with a large volume of coverage. In this study we validated the use of PC VIPR data for the estimation of PVR in a canine model of acute pulmonary arterial hypertension.

16:12 0665.   
Highly Accelerated 4D MR Flow Measurements in Congenital Heart Disease
Daniel Giese1,2, Gerald Greil1, Tobias Schaeffter1, and Sebastian Kozerke1,2
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom, 2Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Especially due to its long acquisition times, 4D Flow MRI often remains compromised in a clinical routine setting. Scan acceleration techniques have been proposed to alleviate this issue. In the present work we demonstrate the potential of using highly undersampled 4D Flow MRI reconstructed using k-t PCA in imaging of congenital heart disease patients (CHD). Patients with different pathologies were scanned and initial results prove that volume flow compares well with fully sampled 2D Flow MRI and that particle tracking exhibits additional clinically valuable information.

16:24 0666.   
Ischemic Mitral Regurgitation Contributes to Alterations in Left Ventricular Three-Dimensional Intracardiac Flow Patterns
Melissa M. Levack1, Walter R.T. Witschey1, Jeremy R. McGarvey1, Kevin Koomalsingh1, Gerald A. Zsido1, Norihiro Kondo1, Manabu Takebe1, Chun Xu1, Francisco Contijoch1, Alexander Barker2, Michael Markl3, Joseph H. Gorman1, James J. Pilla1, and Robert C. Gorman1
1University of Pennsylvania, Philadelphia, PA, United States, 2Radiology, University Medical Center, Freiburg, Germany, 3Department of Radiology, Northwestern University, Chicago, IL, United States

Brief description: To assess and quantify left ventricular (LV) three-dimensional intracardiac blood flow patterns in ischemic mitral regurgitation (IMR). Methods: Ten animals (5 control and 5 IMR) underwent a 4D time-resolved, flow sensitive MRI imaging protocol. Transvalvular flows, sphericity index (SI), LV volumes and vortex ring quantification were calculated. Results: SI for control animals was 0.11 ± 0.01 and increased to 0.24 ± 0.02 (P<0.001) for ischemic animals. Average peak curl in IMR was 0.048 ± 0.004 1/sec (0.061 ± 0.007 1/sec, P<0.05). Discussion: IMR leads to asymmetric ventricular vortex formation which correlates with increases in SI during LV remodeling.

16:36 0667.   
Assessment of Left Ventricular 2D Flow Pathlines during Early Diastole Using SPAMM-PAV: a study in normal volunteers and canine models with reperfused infarcts
Ziheng Zhang1, Daniel Friedman1,2, Donald P Dione3, Ben A Lin3, James S Duncan4, Albert J Sinusas3, and Smita Sampath1
1Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT, United States, 2Department of Mechanical Engineering, University of Pennsylvania School of Engineering and Applied Sciences, philadelphia, PA, United States, 3Department of Medicine, Section of Cardiovascular Medicine, Yale University School of Medicine, 4Department of Biomedical Engineering and Diagnostic Radiology, Yale University

The functional mechanisms involved in adverse left ventricular remodeling caused by reperfusion injury are unclear. We have developed a new high temporal resolution MR imaging technique, SPAMM-PAV (SPAtially Modulated Magnetization with Polarity Alternated Velocity encoding) that provides simultaneous regional assessment of flow velocities and myocardial strains during early diastole. Using this method, we performed flow pathline analysis, (1) to study the impact of RI on the nature of filling patterns and (2) to develop a novel index of filling efficiency, characterized by the kinetic energy of flow pathlines during early diastole.

16:48 0668.   
4D Flow MRI in aortic valve disease demonstrates altered distribution of aortic blood flow helicity
Ramona Lorenz1, Jelena Bock1, Alexander Jonathan Barker1, Florian von Knobelsdorff-Brenkenhoff2, Jan Gerrit Korvink3,4, and Michael Markl5
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Dept. of Cardiology and Nephrology, Charité Medical University Berlin, Working group on cardiovascular MRI, and HELIOS Klinikum Berlin-B, Berlin, Germany, 3Dept. of Microsystems Engineering - IMTEK, University of Freiburg, Freiburg, Germany, 4Freiburg Institute of Advanced Studies (FRIAS), University Freiburg, Freiburg, Germany, 5Dept. of Radiology and Biomedical Engineering, Northwestern University, Chicago, United States

This study provides a quantitative analysis of blood flow helicity within the aorta using 4D flow sensitive MRI. Helical flow was evaluated in a study with 12 healthy volunteers and 20 patients with aortic valve disease. Time resolved mean helicity along the entire aorta was quantified for each subject with good test-retest reliability. All healthy subjects show a consistent direction of rotation over the entire aorta with increased helicity in the aortic arch and good inter-individual agreement, while patients reveal strong variations in the distribution and a significant increase of helical flow in the aorta.

17:00 0669.   
Quantification and visualization of flow in small vessels of the Circle of Willis: time-resolved three-dimensional phase contrast MRI at 7T compared with 3T
Pim van Ooij1,2, Jaco J. M. Zwanenburg3,4, Fredy Visser3, Charles B. Majoie1, Ed vanBavel2, Jeroen Hendrikse3, and Aart J. Nederveen1
1Radiology, Academic Medical Center, Amsterdam, Netherlands, 2Biomedical Engineering & Physics, Academic Medical Center, Amsterdam, Netherlands, 3Radiology, University Medical Center Utrecht, Netherlands, 4Image Sciences Institute, University Medical Center Utrecht, Netherlands

Time-resolved 3D phase contrast MRI was performed in the Circle of Willis of five volunteers at 3T and 7T to investigate the differences in SNR and accuracy of blood flow quantification and visualization. At 7T the direction of the flow in the Anterior Communicating Arteries and Posterior Communicating Arteries was more distinct than at 3T. Increased signal and decreased noise levels at 7T compared to 3T enhance segmentation and allow for better quantification and visualization of flow in small vessels in the Circle of Willis.

17:12 0670.   
Radial Fourier velocity endcoding (rFVE) with SPIRiT exploiting temporal correlations in k-t space
Claudio Santelli1,2, Sebastian Kozerke1,2, and Tobias Schaeffter2
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, 2Division of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom

Fourier velocity encoding (FVE) resolves the distribution of velocities within a voxel by acquiring a range of kv-points. The The long acquisition times, however, have excluded the method from clinical use so far. SPIRiT provides a very general reconstruction framework for non-Cartesian undersampled data. Prior assumption of Gaussian velocity spectra additionally allows undersampling along the velocity encoding dimensions. We extended non-Cartesian SPIRiT to include the temporal dimension thereby additionally exploiting temporal correlations in k-t space. The k-t method is applied to non-uniformly undersampled kv-encodes to reconstruct mean and standard deviation of the velocity spectra for each voxel in aortic flow measurements.

17:24 0671.   
Direct quantification of turbulent shear stresses by multi-point phase-contrast MRI
Christian Binter1, Verena Knobloch1, Andreas Sigfridsson1, and Sebastian Kozerke1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

Excessive shear stresses in pathological flow situations can lead to platelet activation and damage of red blood cells. In-vivo assessment of shear stresses has, however, been impractical. In the present work it is demonstrated that turbulent shear stresses can be determined non-invasively using generalized phase-contrast MRI. Multi-point velocity encoding is employed to obtain information about velocity fluctuations along multiple directions, which permits quantification of turbulent kinetic energy and turbulent shear stresses. Measurements of artificial aortic valves in phantoms and in volunteers demonstrate the feasibility of the method in-vitro and in-vivo.

17:36 0672.   
Velocity Unwrap for High Resolution Slice-Selective Fourier Velocity Encoding Using Spiral SENSE
Jennifer Anne Steeden1, Alexander Jones1, David Atkinson2, Andrew M Taylor1, and Vivek Muthurangu1
1UCL Institute of Cardiovascular Science, London, UK, United Kingdom, 2Department of Medical Physics and Bioengineering, UCL, London, UK, United Kingdom

Quantification of peak velocity is important in the assessment of stenotic flow jets. It is possible to measure peak velocity accurately using Fourier Velocity Encoding (FVE). In this study, a fast, high-resolution slice-selective FVE sequence was developed with the use of spiral trajectories, parallel-imaging, partial-Fourier in the velocity-dimension and a novel velocity-unwrap technique. The resulting sequence was acquired within a short breath-hold. Peak velocities were compared from Doppler ultrasound (US), phase-contrast MR (PCMR) and FVE. Experiments carried out in-vitro and in-vivo showed that PCMR tended to underestimate peak velocity compared to Doppler US, whereas FVE agreed well with Doppler US.

17:48 0673.   
Real-time cardiovascular PC imaging using undersampled radial FLASH and nonlinear inverse reconstruction
Arun Antony Joseph1, Dirk Voit1, Klaus Dietmar Merboldt1, Martin Uecker1,2, Shuo Zhang1, and Jens Frahm1
1Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany, 2Electrical Engineering and Computer Science, University of California, Berkeley, United States

A method for real time phase contrast imaging with highly undersampled FLASH and regularized nonlinear inversion reconstruction was developed. High temporal resolution of 42.5 ms per phase contrast map avoids the temporal and/or spatial averaging effect common in Cine Phase Contrast Imaging. Variations of flow parameters for through plane flow of the ascending and descending aorta with respect to individual heart cycles and respiration were analyzed.