Velocity & Flow

Wednesday 14 May 2014

Tamer Basha¹, Kraig V. Kissinger¹, Beth Goddu¹, Sophie Berg¹, Warren J Manning^1,2, and Reza Nezafat^1
1Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States, ²Radiology, Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States

4D flow imaging using phase contrast CMR (PC CMR) allows visualization and quantification of blood flow. One of the major limitations of 4D flow imaging is its long scan time. In this study, we investigate an accelerated 4D flow imaging sequence that combines an efficient data sampling strategy using echo planar imaging (EPI) with randomly undersampled 3D k-space sampling pattern. The randomly undersampled k-space data are then reconstructed using compressed sensing (CS).

Jennifer Anne Steeden¹, Grzegorz Kowalik¹, Andrew Taylor¹, and Vivek Muthurangu^1
1Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science, London, United Kingdom

Renal artery blood flow (RABF) can be accurately measured using phase contrast MR (PCMR), however long scan times are required. This study proposes averaging data over an integer number of r-r intervals to measure RABF with high spatial resolution during a single breath-hold (~6 seconds). A novel golden-angle spiral PCMR sequence was tested in-vivo (N=30), and the limitations of the technique were tested in an in-silico experiment. In-silico the stroke volumes (SV) measured were within 6% of the true SV, for all heart rates and vessel expansibility tested. In-vivo SVs correlated well with a reference Cartesian PCMR sequence (r=0.9906, P<0.0001).

Julio Andres Sotelo^1,2, Jesús Urbina^3,4, Cristian Tejos^3,5, Israel Valverde^6,7, Daniel Hurtado^8,9, and Sergio Uribe^3,4
1Biomedical Imaging Center, Pontificia Universidad Catolica de Chile, Santiago, Santiago, Chile, ²Electrical Engineering, Pontificia Universidad Catolica de Chile, Santiago, Santiago, Chile, ³Biomedical Imaging Center, Pontificia Universidad Catolica de Chile, Santiago, Chile, ⁴Radiology, School of Medicine, Pontificia Universidad Catolica de Chile, Santiago, Chile, ⁵Electrical Engineering, Pontificia Universidad Catolica de Chile, Santiago, Chile, ⁶Pediatric Cardiology Unit, Hospital Virgen del Rocio, Sevilla, Spain, ⁷Division of Cardiovascular Physiology, Institute of Biomedicine Seville (IBIS), Hospital Universitario Virgen de Rocio/CSIC/University of Seville, Sevilla, Spain, ⁸Biomedical Engineering Group, Pontificia Universidad Catolica de Chile, Santiago, Chile, ⁹Structural Engineering, Pontificia Universidad Catolica de Chile, Santiago, Chile

We propose a novel methodology to compute the WSS in 3D of whole thoracic aorta from 3D CINE PC-MRI. The velocity data is interpolated using tetrahedral finite-elements and the WSS is obtained from a global least-squares stress-projection method. We report and compared the WSS with 2D approximation in the aorta of 15 volunteers and one phantom. Our results showed the local WSS values were in good agreement with the 2D approximation. To the best of our knowledge this is the first work that presents the calculation of a 3D WSS map from 3D PC-MRI data.

Bradley D Allen¹, Pim van Ooij¹, Alex J. Barker¹, Maria Carr¹, Maya Gabbour², Michael Markl^1,3, Cynthia K Rigsby², and Joshua D Robinson^4
1Department of Radiology, Northwestern University, Chicago, IL, United States, ²Department of Medical Imaging, Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, IL, United States, ³Department of Biomedical Engineering, Northwestern University, Chicago, IL, United States, ⁴Division of Pediatric Cardiology, Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, IL, United States

Pediatric bicuspid aortic valve (BAV) patients are not at increased risk of cardiovascular complications during childhood, but often require surgical management of their disease to limit progressive ascending aorta (AAo) dilation and reduce their risk of events in adulthood. Wall shear stress (WSS) has been shown to lead to vascular remodeling and may be the hemodynamic driver of progressive AAo dilation in these patient. In this study, 4D flow MRI was used to non-invasively quantify 3D WSS in the aorta of pediatric BAV patients, and WSS was found to correlate with AAo diameter and peak velocity.

Susanne Schnell¹, Alex J Barker¹, Pegah Entezari¹, A Reza Hornamand¹, Pim van Ooij¹, S Chris Malaisrie², Patrick M McCarthy², Jeremy Collins¹, James C Carr¹, and Michael Markl^1,3
1Radiology, Northwestern University, Chicago, Illinois, United States, ²Surgery, Cardiac Surgery Division, Northwestern University, Chicago, Illinois, United States, ³Biomedical Engineering, Northwestern University, Evanston, Illinois, United States

We evaluated flow dynamics, aorta diameter and geometry in relatives with a family member expressing a bicuspid aortic valve (BAV) and compared results to normal volunteers using contrast enhanced cardiac MRI and 4D flow MRI. The findings demonstrate subtle but significant differences in aortic hemodynamics in BAV relatives compared to age-matched normal controls. Of note, BAV relatives expressed more cubic shaped aortas, which may explain the observed differences. In fact, the significant higher vortex flow in the BAV relatives in the ascending and descending, as well as the significantly lower WSS was related to cubic aortic shape.

Jad Bou Ayache¹, Zoran Stankovic¹, Edouard Semaan¹, James C Carr¹, Michael Markl¹, and Jeremy D Collins^1
1Radiology Department, Feinberg School of Medicine, Chicago, Illinois, United States

Hypersplenism is a well-recognized, treatable cause of thrombocytopenia. However, the underlying flow disturbances contributing to platelet sequestration by the spleen are unknown. Liver donation, hematologic malignancy and liver cirrhosis predisposes to splenomegaly associated with various degrees of thrombocytopenia. We hypothesized that differences in splenic hemodynamics could explain the increased filtration effect independent of splenic size. 4D flow MRI was performed in patients with liver disease and healthy volunteers, correlating indexed splenic arterial and venous flow with platelet counts. Our feasibility study demonstrates significant differences in indexed splenic hemodynamics between patients with and without thrombocytopenia.

Daniel Jeong¹, Alejandro Roldan-Alzate¹, Sharda Srinivasan², Luke J. Lamers², Petros Anagnostopoulos³, Mark L. Schiebler¹, Oliver Wieben^1,4, and Christopher J. Francois^1
1Radiology, University of Wisconsin-Madison, Madison, WI, United States, ²Pediatrics, University of Wisconsin-Madison, Madison, United States, ³Surgery, Madison, United States, ⁴Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States

In this study we compared the efficiency of the right and left ventricles to generate cardiac output in subjects with repaired tetralogy of Fallot (rTOF) and healthy volunteers. 4D Flow MRI was used to calculate ventricular kinetic energy and great vessel flow. Significant differences in ventricular efficiency were observed between the two cohorts, with subjects with rTOF much less efficient than healthy volunteers.

Christopher J Francois¹, Alejandro Roldan-Alzate¹, Oliver Wieben^1,2, Naomi C Chesler³, Sanjiv Shah⁴, Pegah Entezari⁵, James C Carr⁵, Michael Markl^5,6, and Alex Barker^5,6
1Radiology, University of Wisconsin - Madison, Madison, WI, United States, ²Medical Physics, University of Wisconsin - Madison, WI, United States,³Biomedical Engineering, University of Wisconsin - Madison, WI, United States, ⁴Medicine, Northwestern University, IL, United States, ⁵Radiology, Northwestern University, IL, United States, ⁶Biomedical Engineering, Northwestern University, IL, United States

This two-center study compares pulmonary artery flow and wall shear stress (WSS) measurements derived from two different 4D Flow MRI sequences in subjects with pulmonary hypertension (PH) and healthy controls. Significant differences in flow and WSS were observed between PH and control groups. Interobserver variability for these measurements were negligible.

Hadrien Dyvorne¹, Ashley Knight-Greenfield¹, Guido Jajamovich¹, Cecilia Besa¹, Aurelien F Stalder², Julio Garcia Flores³, Michael Markl³, and Bachir Taouli^1
1Icahn School of Medicine at Mount Sinai, New York, NY, United States, ²Siemens AG – Healthcare sector, Erlangen, Germany, ³Radiology, Feinberg School of Medicine, Northwestern Univeresity, Chicago, IL, United States

A new technique was developed to perform fast acquisition of 4D flow in abdominal vessels. By combining undersampled spiral sampling and dynamic compressed sensing reconstruction, 4D flow could be acquired in significantly shorter time, down to a breath hold. In 5 subjects, the novel technique shows high correlation with a standard Cartesian 4D flow measurement and good agreement with 2D phase contrast. Accelerated spiral 4D flow has high potential for comprehensive assessment of hemodynamics in a clinically acceptable scan time.

Christoph Müller¹, Waltraud Brigitte Buchenberg¹, Christoph Benk², Ramona Lorenz¹, Stephan Berner¹, and Bernd Jung^1
1Dept. of Radiology, Medical Physics, University Medical Center, Freiburg, Germany, ²Dept. of Cardiovascular Surgery, Heart Center Freiburg, University Freiburg, Germany

Since in vivo MR studies of ventricular assist devices (VAD) patients are not possible, in vitro models are an important tool to assess flow alterations caused by VADs. For instance they allow for characterizing the impact of different cannula positions or different operating conditions on the hemodynamics. Using an in vitro MR compatible model system this work investigated the flow characteristics of a VAD with a blood supply via the right subclavian artery (SCA) as commonly used in cardio-thoracic surgery in the recent past. 4D phase contrast (PC)-MRI was used for qualitative and quantitative evaluation of flow characteristics.