Vali, Alireza

BackgroundStroke etiology is undetermined in approximately one‐sixth to one‐third of patients. The presence of aortic flow reversal and plaques in the descending aorta (DAo) has been identified as a potential retrograde embolic mechanism.PurposeTo assess the relationships between aortic stiffness, wall thickness, and flow reversal in patients with cryptogenic stroke and healthy controls.Study TypeProspective.PopulationTwenty one patients with cryptogenic stroke and proven DAo plaques (69 ± 9 years, 43% female), 18 age‐matched controls (age: 65 ± 8 years, 61% female), and 14 younger controls (36 ± 9 years, 57% female).Field Strength/Sequence1.5T; 4D flow MRI and 3D dark blood T1‐weighted turbo spin echo MRI of the aorta.AssessmentNoncontrast aortic 4D flow MRI to measure 3D flow dynamics and 3D dark blood aortic wall MRI to assess wall thickness. 4D flow MRI analysis included automated quantification of aortic stiffness by pulse wave velocity (PWV) and voxelwise mapping of the flow reversal fraction (FRF).Statistical TestsAnalysis of variance (ANOVA) or Kruskal–Wallis tests, Student's unpaired t‐tests or Wilcoxon rank‐sum tests, regression analysis.ResultsAortic PWV and FRF were statistically higher in patients (8.9 ± 1.7 m/s, 18.4 ± 7.7%) than younger controls (5.3 ± 0.8 m/s, P < 0.0167; 8.5 ± 2.9%, P < 0.0167), but not age‐matched controls (8.2 ± 1.6 m/s, P = 0.22; 15.6 ± 5.8%, P = 0.22). Maximum aortic wall thickness was higher in patients (3.1 ± 0.7 mm) than younger controls (2.2 ± 0.2 mm, P < 0.0167) and age‐matched controls (2.7 ± 0.5 mm) (P < 0.0167). For all subjects, positive relationships were found between PWV and age (R2 = 0.71, P < 0.05), aortic wall thickness (R2 = 0.20, P < 0.05), and FRF (R2 = 0.47, P < 0.05). Patients demonstrated relationships between PWV and FRF in the ascending aorta (R2 = 0.32, P < 0.05) and arch (R2 = 0.24, P < 0.05).Data ConclusionThis study showed the utility of 4D flow MRI for evaluating aortic PWV and voxelwise flow reversal. Positive relationships between aortic PWV, wall thickness, and flow reversal support the hypothesis that aortic stiffness is involved in this retrograde embolic mechanism.Level of Evidence2Technical Efficacy Stage1

Background Blood flow reversal is a possible mechanism for retrograde embolism in the setting of high‐risk atherosclerotic plaques in the descending aorta (DAo). Evidence suggests that pulse wave velocity (PWV) is a determinant of blood flow reversal and can be reduced by the destiffening effect of renin‐angiotensin system inhibitors (RASI). Purpose To evaluate the impact of antihypertensive therapy on in vivo changes in PWV and flow reversal in patients with cryptogenic stroke. Study Type Prospective. Population Sixteen patients (69 ± 9 years; 10 males) included after cryptogenic stroke. Field Strength/Sequence 3T. 4D flow sequence (temporal resolution = 19.6 msec) Assessment Patients underwent aortic MRI at baseline and at 6‐month follow‐up. Patients received standard‐of‐care antihypertensive therapy that were classified as RASI vs. non‐RASI medications (ie, destiffening vs. nondestiffening).We compared aortic PWV, flow reversal fraction (FRF), aortic measurements, cardiac function, and other aortic and cardiac measurements in the antihypertensive therapy groups. Statistical Tests Two‐tailed paired or unpaired Student's t ‐tests (normal distributions) or Wilcoxon tests (nonnormal distribution). Univariate correlations using Pearson correlation coefficients. Results There was a significant decrease in PWV in the RASI ( n = 10) group (9.4 ± 1.6 m/s vs. 8.3 ± 1.9 m/s; P < 0.05), as well as FRF (18.6% ± 4.1% vs. 16.3% ± 4.0%; P < 0.05) between baseline and the 6‐month MRI studies. There were no changes in PWV or FRF in the non‐RASI ( n = 6) group ( P = 0.146 and P = 0.32). A decrease in FRF was significantly correlated with a decrease in PWV ( r = 0.53; P < 0.05). Data Conclusion The findings of our study suggest that RASI therapy after cryptogenic stroke resulted in a decrease of blood flow reversal and aortic stiffness. Evidence Level 1 Technical Efficacy Stage 4

BackgroundSystematic evaluation of complex flow in the true lumen and false lumen (TL, FL) is needed to better understand which patients with chronic descending aortic dissection (DAD) are predisposed to complications.PurposeTo develop quantitative hemodynamic maps from 4D flow MRI for evaluating TL and FL flow characteristics.Study TypeRetrospective.PopulationIn all, 20 DAD patients (age = 60 ± 11 years; 12 male) (six medically managed type B AD [TBAD], 14 repaired type A AD [rTAAD] now with ascending aortic graft [AAo] or elephant trunk [ET1] repair) and 21 age‐matched controls (age = 59 ± 10 years; 13 male) were included.Field Strength/Sequence1.5T, 3T, 4D flow MRI.Assessment4D flow MRI was acquired in all subjects. Data analysis included 3D segmentation of TL and FL and voxelwise calculation of forward flow, reverse flow, flow stasis, and kinetic energy as quantitative hemodynamics maps.Statistical TestsAnalysis of variance (ANOVA) or Kruskal–Wallis tests were performed for comparing subject groups. Correlation and Bland–Altman analysis was performed for the interobserver study.ResultsPatients with rTAAD presented with elevated TL reverse flow (AAo repair: P = 0.004, ET1: P = 0.018) and increased TL kinetic energy (AAo repair: P = 0.0002, ET1: P = 0.011) compared to controls. In addition, TL kinetic energy was increased vs. patients with TBAD (AAo repair: P = 0.021, ET1: P = 0.048). rTAAD was associated with higher FL kinetic energy and lower FL stasis compared to patients with TBAD (AAo repair: P = 0.002, ET1: P = 0.024 and AAo repair: P = 0.003, ET1: P = 0.048, respectively).Data ConclusionQuantitative maps from 4D flow MRI demonstrated global and regional hemodynamic differences between DAD patients and controls. Patients with rTAAD vs. TBAD had significantly altered regional TL and FL hemodynamics. These findings indicate the potential of 4D flow MRI‐derived hemodynamic maps to help better evaluate patients with DAD.Level of Evidence: 3Technical Efficacy Stage: 1J. Magn. Reson. Imaging 2020;51:1357–1368.