Purpose The purpose of this study was to evaluate the utility of k-t parallel imaging for accelerating aortic four-dimensional (4D)-flow MRI. The aim was to systematically investigate the impact of different acceleration factors and number of coil elements on acquisition time, image quality and quantification of hemodynamic parameters. Methods k-t accelerated 4D-flow MRI (spatial/temporal resolution = 2.1 × 2.5 × 2.5 mm/40.0 ms) was acquired in 10 healthy volunteers with acceleration factors R = 3, 5, and 8 using 12- and 32-channel receiver coils. Results were compared with conventional parallel imaging (GRAPPA [generalized autocalibrating partial parallel acquisition], R = 2). Data analysis included radiological grading of three-dimensional blood flow visualization quality as well as quantification of blood flow, velocities and wall shear stress (WSS). Results k-t GRAPPA significantly reduced scan time by 28%, 54%, and 68%, for R = 3, 5, and 8, respectively, while maintaining image quality as demonstrated by overall similar image quality grading. Significant differences in peak WSS (diff12ch = −5.9%, diff32ch = 18.5%) and mean WSS (diff32ch = 13.9%) were found at the descending aorta for both receiver coils for R = 5 (PWSS < 0.04). Peak velocity differed for R=8 at the aortic root (−7.4%) and descending aorta (−12%) with PpeakVelo < 0.03. Conclusion k-t GRAPPA acceleration with a 12- or 32- channel receiver coil and an acceleration of 3 or 5 can compete with a standard GRAPPA R = 2 acceleration.

Background The purpose is to compare aortic hemodynamics and blood flow patterns using in-vivo 4D flow MRI in patients following valve-sparing aortic root replacement (VSARR) and aortic root replacement with bio-prosthetic valves (BIO-ARR). Methods In-vivo 4D flow MRI was performed in 11 patients after VSARR (47±18 years, 6 BAV, 5 TAV), 16 patients after BIO-ARR (52±14 years), and 10 healthy controls (47±16 years). Analysis included 3D blood flow visualization and grading of helix flow in the ascending aorta (AAo) and arch. Peak systolic velocity was quantified in 9 analysis planes in the AAo, aortic arch, and descending aorta. Flow profile uniformity was evaluated in the aortic root and ascending aorta. Results Peak systolic velocity (2.0–2.5m/s) in the aortic root and AAo in both VSARR and BIO-ARR were elevated compared to controls (1.1–1.3m/s, p < 0.005). Flow asymmetry in BIO-ARR was increased compared to VSARR, evidenced by more AAo outflow jets (9 of 16 BIO-ARR, 0 of 11 in VSARR). BIO-ARR exhibited significantly (p<0.001) increased helix flow in the AAo as a measure of increased flow derangement. Finally, peak systolic velocities were elevated at the aortic root for BIO-ARR (2.5 vs 2.0m/s, p < 0.05) but lower in the distal AAo when compared to VSARR.. Conclusion VSARR results in improved hemodynamic outcomes when compared with BIO-ARR as indicated by reduced peak velocities in the aortic root and less helix flow in the AAo by 4D flow MRI. Longitudinal research assessing the clinical impact of these differences in hemodynamic outcomes is warranted.

VSARR restored a cohesive flow pattern independent of native valve morphology but resulted in increased peak velocities throughout the aorta. 4D flow MRI methods can assess the clinical implications of altered aortic flow dynamics in patients undergoing VSARR.

Our analysis suggests that almost 10% of CAS and CEA is performed in patients with atrial fibrillation in general practice, and higher rates of adverse events are observed among these patients, particularly those undergoing CEA.

Objectives To test the hypothesis that variants in cerebrovascular anatomy will affect the number of patients demonstrating a plausible retrograde embolization mechanism from plaques in the descending aorta (DAo). Methods Thirty-five patients (63±17years) with cryptogenic stroke underwent 4D flow MRI for the assessment of aortic 3D blood flow and MR angiography for the evaluation of Circle of Willis, posterior circulation, and aortic arch architecture. In patients with proven DAo plaque, retrograde embolization was considered a potential mechanism if retrograde flow extended from the DAo to a supra-aortic vessel supplying the cerebral infarct territory. Results Retrograde embolization with matching cerebral infarct territory was detected in 6 (17%) patients. Circle of Willis and aortic arch variant anatomy was found in 60% of patients which led to the reclassification of retrograde embolization risk as present in 3 (9%) additional patients for a total 26% of cryptogenic stroke patients. Conclusion 4D flow MRI demonstrated 26% concordance with infarct location on imaging with retrograde diastolic flow into the feeding vessels of the affected cerebral area, identifying a potential etiology for cryptogenic stroke. Our findings further demonstrate the importance of cerebrovascular anatomy when determining concordance of retrograde flow pathways with vascular stroke territory from DAo plaques.