Scan–rescan reproducibility of segmental aortic wall shear stress as assessed by phase-specific segmentation with 4D flow MRI in healthy volunteers

Abstract

ObjectiveThe aim was to investigate scan–rescan reproducibility and observer variability of segmental aortic 3D systolic wall shear stress (WSS) by phase-specific segmentation with 4D flow MRI in healthy volunteers.Materials and methodsTen healthy volunteers (age 26.5 ± 2.6 years) underwent aortic 4D flow MRI twice. Maximum 3D systolic WSS (WSSmax) and mean 3D systolic WSS (WSSmean) for five thoracic aortic segments over five systolic cardiac phases by phase-specific segmentations were calculated. Scan–rescan analysis and observer reproducibility analysis were performed.ResultsScan–rescan data showed overall good reproducibility for WSSmean (coefficient of variation, COV 10–15%) with moderate-to-strong intraclass correlation coefficient (ICC 0.63–0.89). The variability in WSSmax was high (COV 16–31%) with moderate-to-good ICC (0.55–0.79) for different aortic segments. Intra- and interobserver reproducibility was good-to-excellent for regional aortic WSSmax (ICC ≥ 0.78; COV ≤ 17%) and strong-to-excellent for WSSmean (ICC ≥ 0.86; COV ≤ 11%). In general, ascending aortic segments showed more WSSmax/WSSmean variability compared to aortic arch or descending aortic segments for scan–rescan, intraobserver and interobserver comparison.ConclusionsScan–rescan reproducibility was good for WSSmean and moderate for WSSmax for all thoracic aortic segments over multiple systolic phases in healthy volunteers. Intra/interobserver reproducibility for segmental WSS assessment was good-to-excellent. Variability of WSSmax is higher and should be taken into account in case of individual follow-up or in comparative rest–stress studies to avoid misinterpretation.Electronic supplementary materialThe online version of this article (10.1007/s10334-018-0688-6) contains supplementary material, which is available to authorized users.

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“…Moreover, patients were analyzed with the software for which a 3D WSS reproducibility analysis study showed robustness of the segmentation and WSS analysis method. 16 Furthermore, the robustness and reproducibility of 2D WSS analysis in crosssectional planes has been previously demonstrated. 36 However, WSS determination in the neo-aortic root remains a challenge because of the aortic motion and the presence of slow and recirculating flow.…”

“…The 4D flow segmentation was performed as previously described. 16 In short, from the 4D flow raw data ( Fig. 1a) the peak systolic phase was automatically detected by the CAAS MR Flow software program by identification of the cardiac phase with the highest variance in the 3D velocity dataset.…”

“…36 However, WSS determination in the neo-aortic root remains a challenge because of the aortic motion and the presence of slow and recirculating flow. Although we did perform a timeresolved segmentation method to account for aortic motion, 16 small border errors may be present for the calculated WSS in the neo-aortic root region, implying that it may not actually reflect the stress on the wall.…”

“…All healthy subjects underwent the same MRI assessment of the heart and great vessels including 4D flow aortic imaging as part of a validation study. 16…”

“…After factorizing the velocity profile into its component parallel to the aortic lumen wall, the systolic WSS was computed by the first derivative of a quadratic approximation of that velocity profile at the location of the aortic lumen wall. 16 Similarities between the location of FD and the location of the highest systolic WSS were evaluated by determining the absolute difference between these locations. The number of octant positions clockwise or counterclockwise away from the position of the FD location was calculated and categorized as follows: 0 = no difference in location; 1 = difference of one octant position; 2 = difference of two octant positions; 3 = difference of three octant positions; 4 = difference of four octant positions.…”