Go with the Flow
Tuesday 21 April 2009
Room 312 16:00-18:00

Moderators:

 Jelena Bock and Georg M. Bongartz
 
16:00  317. Flow Assessment Over All Heart Valves Simultaneously Using 3D Velocity-Encoded MRI with Retrospective Valve Tracking
    Jos J.M. Westenberg1, Stijntje D. Roes1, Sebastiaan Hammer2, Pieter J. van den Boogaard1, Nina Ajmone Marsan3, Jeroen J. Bax3, Johan H.C. Reiber1, Albert de Roos1, Rob J. van der Geest1
1Radiology, Leiden University Medical Center, Leiden, Netherlands; 2Internal Medicine, Leiden University Medical Center, Leiden, Netherlands; 3Cardiology, Leiden University Medical Center, Leiden, Netherlands
    Conventional 2-dimensional one-directional through-plane velocity-encoded MRI not only extents imaging time when the flow through all heart valves needs to be studied sequentially, but also shows low agreement in net flow volume between the four valves. Three-dimensional three-directional velocity-encoded MRI with retrospective valve tracking during offline analysis is introduced for simultaneous flow assessment at all four heart valves in less than 5 minutes scan time. This technique is applied to 16 volunteers without valve regurgitation and 29 patients with valve regurgitation. The net flow volumes show good agreement between the valves. Regurgitation and net flow can be quantified accurately.
     
16:12 318. Pressure Gradient Wave Propagation in the Left Atrium and Left Ventricle During Early Diastole
    June Cheng Baron1, Ben Esch2, Jessica Scott2, Mark Haykowsky3, Ian Paterson4, Richard Thompson1
1Biomedical Engineering, University of Alberta, Edmonton, AB, Canada; 2Cardiovascular Physiology and Rehabilitation Laboratory, University of British Columbia, Vancouver, BC, Canada; 3Physical Therapy, University of Alberta, Edmonton, AB, Canada; 4Division of Cardiology, University of Alberta, Edmonton, AB, Canada
    Pressure gradients are an appealing measure of diastolic function because they provide a direct assessment of the forces responsible for driving blood flow, and have now been reported in several clinical studies. While pressure gradients are commonly expressed in terms of a peak pressure difference over space at a single point in time they vary considerably over time and space, with unique patterns in the atrium and ventricle. We show, for the first time, that pressure gradients, calculated using phase contrast MRI, present as distinct ventricular and atrial waves with characteristic speeds, directions and amplitudes.
     
16:24 319. 4D Flow of the Whole Heart and Great Vessels Using a Real Time Self Respiratory Gating Technique: A Validation Study
    Sergio Andres Uribe Arancibia1, Philipp Beerbaum1, Allan Rasmusson2, Thomas Sorensen2, Reza Razavi1, Tobias Schaeffter1
1Division of Imaging Sciences, King's College London, London, UK; 2Department of Computer Science, University of Aarhus, Aarhus, Denmark
   

In this study we propose to validate a 4D flow technique that acquires data on the whole heart and great vessels using a self-respiratory gating technique. The method allows retrospective flow quantification from data obtained in a single free breathing scan. In 15 volunteers, the method was compared with 2D flows and with a 4D flow data obtained without respiratory gating. Result showed an excellent agreement with the clinically used 2D sequence. When applied in a congenital heart patient the technique showed to be very valuable for retrospective analysis of flow in any arbitrary plane and direction.
     
16:36 320. PC VIPR for Comprehensive Cardiovascular Evaluation in Congenital Heart Disease
    Christopher J. François1, Elizabeth K. Nett2, Benjamin R. Landgraf1, Kevin M. Johnson2, Shardha Srinivasan3, John Carter Ralphe3, Darren P. Lum1, Oliver Wieben2
1Radiology, University of Wisconsin, Madison, WI, USA; 2Medical Physics, University of Wisconsin, Madison, WI, USA; 3Pediatric Cardiology, University of Wisconsin, Madison, WI, USA
    This study demonstrates the feasibility of using phase contrast (PC) vastly undersampled isotropic projection reconstruction (VIPR) for the evaluation of patients with congenital heart disease. The scan is completed during free breathing and provides coverage of the whole chest with isotropic spatial resolution. The data are reconstructed as (1) magnitude images, (2) angiograms, and (3) cine velocity vector fields to quantify flow and other hemodynamic parameters, thereby providing comprehensive information from a single scan. Because PC VIPR does not require the use of contrast material, this sequence can be performed in patients in whom the administration of Gd-based contrast material is not considered safe.
     
16:48 321. Analysis of Aortic Hemodynamics After Treatment for Coarctation Using Flow-Sensitive 4D MRI at 3T
    Alex Frydrychowicz1, Daniel Hirtler2, Raoul Arnold2, Alexander Berger1, Aurelien F. Stalder1, Jelena Bock1, Andreas Harloff3, Mathias Langer1, Jürgen Hennig1, Michael Markl1
1Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany; 2Pediatric Cardiology, University Hospital Freiburg, Freiburg, Germany; 3Neurology, University Hospital Freiburg, Freiburg, Germany
    Surgical repair of aortic coarctation can lead to severe secondary complications such as re-stenosis and aneurysms. It was the aim of this study to investigate the influence of aortic flow alterations on the formation of secondary complications in 24 patients after coarctation repair by means of time-resolved 3-directional flow-sensitive 3D MRI at 3T. 3D visualization using time-resolved particle traces and streamlines revealed the different extent of altered flow patterns associated with the post surgical status of the patient. Characteristic changes in 3D flow patterns hint towards a hemodynamic contribution to the otherwise multifactorial etiology of complications associated with aortic coarctation.
     
17:00 322. Phase Contrast Ultra Short TE; a More Reliable Technique for Measurement of High Velocity Turbulent Stenotic Jets
   

Kieran O'Brien1, Saul Myerson2, Brett Cowan1, Alistair Young1, Matthew Robson2
1University of Auckland, Auckland, New Zealand; 2University of Oxford, Oxford, UK
    The reliability of phase contrast (PC) magnetic resonance velocity measurements in high velocity stenotic jets has been questioned. The best method to reduce errors due to intravoxel dephasing is to shorten the TE; however, in conventional Cartesian PC sequences the TE cannot be shortened adequately for reliable clinical diagnosis. We present an alternative technique that utilizes velocity-dependent selective-slice-excitation and centric-radial readout trajectories to minimize TE. Velocity measurement occurs over the shortest time window resulting in reduced intravoxel dephasing and better agreement with a high velocity (~10m/s) stenotic phantom. Clinical feasibility was demonstrated in a patient with aortic stenosis.
   

 
17:12 323. Three-Dimensional Assessment of Wall Shear Stress Distribution in the Carotid Bifurcation
    Michael Markl1, Felix Wegent2, Simon Bauer1, Aurelien F. Stalder1, Alex Frydrychowicz1, Cornelius Weiller2, Martin Schumacher3, Andreas Harloff2
1Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany; 2Neurology, University Hospital Freiburg, Freiburg, Germany; 3Neuroradiology, University Hospital Freiburg, Freiburg, Germany
    Flow sensitive MRI for the in-vivo quantification of 3D blood-flow and derived vessel wall parameters may provide an enhanced understanding of flow-mediated arterial atherogenesis in the carotid arteries. We evaluated the normal distribution of segmental wall shear stress in 32 normal volunteers based flow-sensitive 4D MRI for full hemodynamic information on 3D blood flow. Analysis of vectorial wall shear stress (WSS) identified carotid segments potentially predisposed to the development of atherosclerosis. Posterior regions demonstrated a high incidence of low absolute WSS and high oscillatory shear index (OSI) offering a potential explanation why carotid stenosis predominantly develops in the ICA bulb.
     
17:24 324. Time-Resolved Blood Flow Quantification Without Gating
    Michael C. Langham1, Jeremy Magland1, Felix W. Wehrli1
1Radiology, University of Pennsylvania, Philadelphia, PA, USA
    In MRI, gated phase-contrast (PC)-MRI is the standard approach to resolving pulsatile blood flow but arrhythmia (which is normal) can significantly affect accuracy and reproducibility since each phase-encoding takes one heartbeat. We describe a flow quantification technique with velocity-encoded projections where reference image is used to remove signals from the background, e.g. tissue, prior to taking phase difference. The projection method achieves temporal resolution of 20 ms without gating (prospective or retrospective). We demonstrate the technique by time-resolving the triphasic pulsatile blood flow in femoral artery of healthy subjects and show that results are consistent with PC-MRI.
     
17:36 325. Evidence Across CMR Sites and Systems of Phase-Contrast Background Velocity Offsets Requiring Correction for Accurate Regurgitant or Shunt Flow
    Peter D. Gatehouse1, Marijn P. Rolf2, Martin J. Graves3, Mark B. Hofman2, John Totman4, Beat Werner5, Rebecca Quest6, Yingmin Liu7, Jochen von Spiczak8, Matthias Dieringer9, Juerg Schwitter10, Jeanette Schulz-Menger9, David N. Firmin1, Philip J. Kilner1
1Royal Brompton Hospital, London, UK; 2VU Medical Center, Amsterdam, Netherlands; 3Addenbrooke's Hospital, Cambridge, UK; 4King's College, London, UK; 5Kinderspital, Zurich, Switzerland; 6Imperial College, London, UK; 7University of Auckland, New Zealand; 8University and ETH, Zurich, Switzerland; 9Charité Universitätsmedizin, Berlin, Germany; 10University Hospital, Zurich, Switzerland
    Velocity offset errors are often reported to damage reliability of cardiac shunt and regurgitation by phase-contrast, hence this inter-site inter-scanner measurement of velocity errors to find out how widespread the problem might be.
     
17:48 326. In Vivo Assessment of Carotid Wall Shear Rate Using Spiral Fourier Velocity Encoding
   

Joao Luiz Azevedo Carvalho1,2, Jon Fredrik Nielsen2,3, Krishna Shrinivas Nayak2
1Electrical Engineering, University of Brasilia, Brasilia, DF, Brazil; 2Electrical Engineering, University of Southern California, Los Angeles, CA, USA; 3Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA
    Wall shear stress is believed to influence the development of atherosclerosis, but there is currently no gold standard for its in vivo measurement. High-resolution phase contrast is inadequate due to partial volume effects, long scan-times, and low SNR. We evaluate the use of spiral Fourier velocity encoding for assessing wall shear rate in the carotid arteries. The shear rate is estimated using the method described by Frayne and Rutt MRM 34:378-387, which estimates the velocity profile within a voxel from its velocity distribution. The proposed method is validated using simulated data from computational fluid dynamics, and demonstrated in vivo at 3T.