Optimization of 4D Flow MRI Spatial and Temporal Resolution for Examining Complex Hemodynamics in the Carotid Artery Bifurcation

• Type of Material: Article
• Authors: Retta El Sayed, Emory University; Sharifi Alireza, Emory University; Charlie C. Park, Emory University; Diogo C. Haussen, Emory University; Jason William Allen, Emory University; John Oshinski, Emory University
• Language: English
• Date: 2023-05-08
• Publisher: Springer Nature
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
• Final Published Version (URL): https://doi.org/10.1007%2Fs13239-023-00667-1
• Title of Journal or Parent Work: Cardiovascular Engineering and Technology
• Volume: 14
• Issue: 3
• Start Page: 476
• End Page: 488
• Grant/Funding Information: This work was funded by the American Heart Association Grant Nos. 0000065426 (Sharifi) and 19IPLOI34760670 (Allen), National Institutes of Health Grant Nos. R21NS114603 (Allen and Oshinski) and R01EB027774 (Oshinski). Additionally, this material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 1937971 (El Sayed).
• Keywords: 4D FLOW; cartoid web; temporal resolution; spatial resolution; 4D fMRI
• Research Categories: Health Sciences, Medicine and Surgery; Engineering, Biomedical; Biophysics, Medical

Abstract

Background Three-dimensional, ECG-gated, time-resolved, three-directional, velocity-encoded phase-contrast MRI (4D flow MRI) has been applied extensively to measure blood velocity in great vessels but has been much less used in diseased carotid arteries. Carotid artery webs (CaW) are non-inflammatory intraluminal shelf-like projections into the internal carotid artery (ICA) bulb that are associated with complex flow and cryptogenic stroke. Purpose: Optimize 4D flow MRI for measuring the velocity field of complex flow in the carotid artery bifurcation model that contains a CaW. Methods: A 3D printed phantom model created from computed tomography angiography (CTA) of a subject with CaW was placed in a pulsatile flow loop within the MRI scanner. 4D Flow MRI images of the phantom were acquired with five different spatial resolutions (0.50–2.00 mm3) and four different temporal resolutions (23–96 ms) and compared to a computational fluid dynamics (CFD) solution of the flow field as a reference. We examined four planes perpendicular to the vessel centerline, one in the common carotid artery (CCA) and three in the internal carotid artery (ICA) where complex flow was expected. At these four planes pixel-by-pixel velocity values, flow, and time average wall shear stress (TAWSS) were compared between 4D flow MRI and CFD. Hypothesis: An optimized 4D flow MRI protocol will provide a good correlation with CFD velocity and TAWSS values in areas of complex flow within a clinically feasible scan time (~ 10 min). Results: Spatial resolution affected the velocity values, time average flow, and TAWSS measurements. Qualitatively, a spatial resolution of 0.50 mm3 resulted in higher noise, while a lower spatial resolution of 1.50–2.00 mm3 did not adequately resolve the velocity profile. Isotropic spatial resolutions of 0.50–1.00 mm3 showed no significant difference in total flow compared to CFD. Pixel-by-pixel velocity correlation coefficients between 4D flow MRI and CFD were > 0.75 for 0.50–1.00 mm3 but were < 0.5 for 1.50 and 2.00 mm3. Regional TAWSS values determined from 4D flow MRI were generally lower than CFD and decreased at lower spatial resolutions (larger pixel sizes). TAWSS differences between 4D flow and CFD were not statistically significant at spatial resolutions of 0.50–1.00 mm3 but were different at 1.50 and 2.00 mm3. Differences in temporal resolution only affected the flow values when temporal resolution was > 48.4 ms; temporal resolution did not affect TAWSS values. Conclusion: A spatial resolution of 0.74–1.00 mm3 and a temporal resolution of 23–48 ms (1–2 k-space segments) provides a 4D flow MRI protocol capable of imaging velocity and TAWSS in regions of complex flow within the carotid bifurcation at a clinically acceptable scan time.