Importance of variants in cerebrovascular anatomy for potential retrograde embolization in cryptogenic stroke.

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 (aged 63 ± 17 years) 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 six (17%) patients. Circle of Willis and aortic arch variant anatomy was found in 60% of patients, leading to reclassification of retrograde embolization risk as present in three (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. KEY POINTS: • Retrograde embolization from descending aortic plaques constitutes a plausible etiology in cryptogenic stroke. • Common variants of cerebrovascular anatomy are important in determining retrograde embolization mechanism. • Variant cerebrovascular anatomy can link retrograde flow pathways with vascular stroke territory.

The effect of atrial fibrillation on outcomes in patients undergoing carotid endarterectomy or stent placement in general practice.

BACKGROUND: Atrial fibrillation is a common comorbid condition among patients undergoing carotid endarterectomy (CEA) and carotid artery stent placement (CAS); however, the outcomes of patients with atrial fibrillation undergoing CAS have not been fully examined. We sought to investigate the impact of atrial fibrillation on outcomes of CEA and CAS in general practice. METHODS: We analyzed the data from the National Inpatient Sample (NIS), which is representative of all admissions in the United States from 2005 to 2009. The primary end point was postoperative stroke, cardiac complication, postoperative mortality, and composite of these end points. Univariate and multivariate regression analyses were performed to determine, first, the association of atrial fibrillation (compared to without atrial fibrillation) and, second, the association of CEA (compared with CAS) in patients with atrial fibrillation with the occurrence of postoperative stroke, cardiac complication, or death. Covariates included in the logistic regression were the patient's gender, age, race/ethnicity, comorbid conditions, and symptom status (symptomatic vs asymptomatic status) and the hospital's characteristics. RESULTS: Of the total 672,074 patients who underwent CAS or CEA, 8.8% (95% confidence interval [CI], 8.7-8.9) of the procedures were performed in patients with atrial fibrillation. Atrial fibrillation was associated with an increased risk of postoperative stroke in patients undergoing CEA (n = 879 [1.7%]; P < .0001; odds ratio [OR], 1.57; 95% CI, 1.32-1.86) but not in patients undergoing CAS. The relative risk of the composite end point of postoperative stroke, cardiac complications, and mortality was increased in patients with atrial fibrillation undergoing CAS (OR, 1.43; 95% CI, 1.18-1.74) and in those undergoing CEA (OR, 3.18; 95% CI, 2.89-3.49). After adjustment for potential confounders, the odds of the composite end point of postoperative stroke, cardiac complications, and mortality (OR, 1.31; 95% CI, 1.08-1.59) in atrial fibrillation patients were significantly higher among patients who underwent CEA (compared with those who underwent CAS). An opposite relationship was seen in patients without atrial fibrillation, in whom the composite end point was significantly lower in patients undergoing CEA. CONCLUSIONS: 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.

K-t GRAPPA-accelerated 4D flow MRI of liver hemodynamics: influence of different acceleration factors on qualitative and quantitative assessment of blood flow.

OBJECTIVE: We sought to evaluate the feasibility of k-t parallel imaging for accelerated 4D flow MRI in the hepatic vascular system by investigating the impact of different acceleration factors. MATERIALS AND METHODS: k-t GRAPPA accelerated 4D flow MRI of the liver vasculature was evaluated in 16 healthy volunteers at 3T with acceleration factors R = 3, R = 5, and R = 8 (2.0 × 2.5 × 2.4 mm(3), TR = 82 ms), and R = 5 (TR = 41 ms); GRAPPA R = 2 was used as the reference standard. Qualitative flow analysis included grading of 3D streamlines and time-resolved particle traces. Quantitative evaluation assessed velocities, net flow, and wall shear stress (WSS). RESULTS: Significant scan time savings were realized for all acceleration factors compared to standard GRAPPA R = 2 (21-71 %) (p < 0.001). Quantification of velocities and net flow offered similar results between k-t GRAPPA R = 3 and R = 5 compared to standard GRAPPA R = 2. Significantly increased leakage artifacts and noise were seen between standard GRAPPA R = 2 and k-t GRAPPA R = 8 (p < 0.001) with significant underestimation of peak velocities and WSS of up to 31 % in the hepatic arterial system (p <0.05). WSS was significantly underestimated up to 13 % in all vessels of the portal venous system for k-t GRAPPA R = 5, while significantly higher values were observed for the same acceleration with higher temporal resolution in two veins (p < 0.05). CONCLUSION: k-t acceleration of 4D flow MRI is feasible for liver hemodynamic assessment with acceleration factors R = 3 and R = 5 resulting in a scan time reduction of at least 40 % with similar quantitation of liver hemodynamics compared with GRAPPA R = 2.

k-t GRAPPA accelerated four-dimensional flow MRI in the aorta: effect on scan time, image quality, and quantification of flow and wall shear stress.

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.

Safety and effectiveness of endovascular treatment after 6 hours of symptom onset in patients with anterior circulation ischemic stroke: a matched case control study.

BACKGROUND: Endovascular treatment within 6 hours of symptom onset appears to be beneficial in carefully selected patients with ischemic stroke. It is unclear whether endovascular treatment beyond 6 hours of symptom onset is safe and efficacious. METHODS: Over a 6-year period, 52 patients with acute ischemic stroke in the anterior circulation underwent emergent endovascular thrombolytic infusion and mechanical thrombectomy after 6 hours of symptom onset at 3 institutions. Their outcomes were compared to 52 placebo-treated patients matched by baseline National Institutes of Health Stroke Scale (NIHSS) score and nonlacunar anterior circulation location from the Trial of Org 10172 in Acute Stroke Treatment trial using a 1:1 ratio. Univariate and multivariate analyses were performed comparing the rates of symptomatic intracerebral hemorrhage, early neurologic improvement, favorable outcome at 7 days or discharge, and in-hospital mortality between the 2 groups. RESULTS: After adjustment for gender, time interval between symptom onset to treatment, hypertension, hyperlipidemia, and history of cigarette smoking, rates of neurologic improvement at 24 hours (odds ratio [OR] 1.15; 95% confidence interval [CI] 0.43-3.1) and favorable outcome at 7 days or discharge (OR 1.39; 95% CI 0.47-4.05) were similar in the 2 groups. No differences in the rates of symptomatic intracerebral hemorrhage or death were found after adjusting for potential confounders. In an analysis limited to only those patients who underwent computed tomographic perfusion or magnetic resonance imaging before receiving endovascular treatment, the rate of favorable outcome at 7 days or discharge was similar between patients who underwent endovascular treatment and control patients (35.7% v 32.1%; P = .77). CONCLUSIONS: We did not observe any evidence of benefit in halting neurologic worsening or improving outcomes among patients undergoing endovascular treatment for treatment of an anterior circulation ischemic stroke after 6 hours of symptom onset. Strong evidence of both the safety and efficacy of emergent endovascular treatment when administered to patients with stroke in the anterior circulation is needed.

Improved respiratory navigator gating for thoracic 4D flow MRI.

BACKGROUND: Thoracic and abdominal 4D flow MRI is typically acquired in combination with navigator respiration control which can result in highly variable scan efficiency (Seff) and thus total scan time due to inter-individual variability in breathing patterns. The aim of this study was to test the feasibility of an improved respiratory control strategy based on diaphragm navigator gating with fixed Seff, respiratory driven phase encoding, and a navigator training phase. METHODS: 4D flow MRI of the thoracic aorta was performed in 10 healthy subjects at 1.5T and 3T systems for the in-vivo assessment of aortic time-resolved 3D blood flow velocities. For each subject, four 4D flow scans (1: conventional navigator gating, 2-4: new implementation with fixed Seff =60%, 80% and 100%) were acquired. Data analysis included semi-quantitative evaluation of image quality of the 4D flow magnitude images (image quality grading on a four point scale), 3D segmentation of the thoracic aorta, and voxel-by-voxel comparisons of systolic 3D flow velocity vector fields between scans. RESULTS: Conventional navigator gating resulted in variable Seff=74±13% (range=56%-100%) due to inter-individual variability of respiration patterns. For scans 2-4, the new navigator implementation was able to achieve predictable total scan times with stable Seff, only depending on heart rate. Semi- and fully quantitative analysis of image quality in 4D flow magnitude images was similar for the new navigator scheme compared to conventional navigator gating. For aortic systolic 3D velocities, good agreement was found between all new navigator settings (scan 2-4) with the conventional navigator gating (scan 1) with best performance for Seff=80% (mean difference=-0.01 m/s; limits of agreement=0.23 m/s, Pearson's ρ=0.89, p<0.001). No significant differences for image quality or 3D systolic velocities were found for 1.5T compared to 3T. CONCLUSIONS: The findings of this study demonstrate the feasibility of the new navigator scheme to acquire 4D flow data with more predictable scan time while maintaining image quality and 3D velocity information, which may prove beneficial for clinical applications.

Comparison of Hemodynamics After Aortic Root Replacement Using Valve-Sparing or Bioprosthetic Valved Conduit.

BACKGROUND: The purpose of this study is to compare aortic hemodynamics and blood flow patterns using in-vivo four-dimensional (4D) flow magnetic resonance imaging (MRI) in patients after valve-sparing aortic root replacement (VSARR) and aortic root replacement with bioprosthetic valves (BIO-ARR). METHODS: In-vivo 4D flow MRI was performed in 11 patients after VSARR (47 ± 18 years, 6 bicuspid aortic valves, 5 trileaflet aortic valves), 16 patients after BIO-ARR (52 ± 14 years), and 10 healthy controls (47 ± 16 years). Analysis included three-dimensional 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 to 2.5m/second) in the aortic root and AAo in both VSARR and BIO-ARR were elevated compared with controls (1.1 to 1.3m/second, p < 0.005). Flow asymmetry in BIO-ARR was increased compared with VSARR, evidenced by more AAo outflow jets (9 of 16 BIO-ARR, 0 of 11 in VSARR). The 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/second, p < 0.05) but lower in the distal AAo when compared with VSARR. CONCLUSIONS: The 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.

Haemodynamic outcome at four-dimensional flow magnetic resonance imaging following valve-sparing aortic root replacement with tricuspid and bicuspid valve morphology.

OBJECTIVE: To provide a more complete characterization of aortic blood flow in patients following valve-sparing aortic root replacement (VSARR) compared with presurgical cohorts matched by tricuspid and bicuspid valve morphology, age and presurgical aorta size. METHODS: Four-dimensional (4D) flow magnetic resonance imaging (MRI) was performed to analyse three-dimensional (3D) blood flow in the thoracic aorta of n = 13 patients after VSARR with reimplantation of native tricuspid aortic valve (TAV, n = 6) and bicuspid aortic valve (BAV, n = 7). Results were compared with presurgical age and aortic size-matched control cohorts with TAV (n = 10) and BAV (n = 10). Pre- and post-surgical aortic flow was evaluated using time-resolved 3D pathlines using a blinded grading system (0-2, 0 = small, 1 = moderate and 2 = prominent) analysing ascending aortic (AAo) helical flow. Systolic flow profile uniformity in the aortic root, proximal and mid-AAo was evaluated using a four-quadrant model. Further analysis in nine analysis planes distributed along the thoracic aorta quantified peak systolic velocity, retrograde fraction and peak systolic flow acceleration. RESULTS: Pronounced AAo helical flow in presurgical control subjects (both BAV and TAV: helix grading = 1.8 ± 0.4) was significantly reduced (0.2 ± 0.4, P < 0.001) in cohorts after VSARR independent of aortic valve morphology. Presurgical AAo flow was highly eccentric for BAV patients but more uniform for TAV. VSARR resulted in less eccentric flow profiles. Systolic peak velocities were significantly (P < 0.05) increased in post-root repair BAV patients throughout the aorta (six of nine analysis planes) and to a lesser extent in TAV patients (three of nine analysis planes). BAV reimplantation resulted in significantly increased peak velocities in the proximal AAo compared with root repair with TAV (2.3 ± 0.6 vs 1.6 ± 0.4 m/s, P = 0.017). Post-surgical patients showed a non-significant trend towards higher systolic flow acceleration as a surrogate measure of reduced aortic compliance. CONCLUSIONS: 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.