Dual echo vessel-encoded ASL for simultaneous BOLD and CBF reactivity assessment in patients with ischemic cerebrovascular disease.

PURPOSE: Blood oxygenation level-dependent (BOLD)-weighted and vessel-encoded arterial spin labeling (VE-ASL) MRI provide complementary information and can be used in sequence to gauge hemodynamic contributions to cerebrovascular reactivity. Here, cerebrovascular reactivity is assessed using dual echo VE-ASL MRI to understand how VE labeling preparations influence BOLD and ASL contrast in flow-limited and healthy perfusion territories. METHODS: Patients (n = 12; age = 55 +/- 14 years; 6F/6M) presenting with ischemic steno-occlusive cerebrovascular disease underwent 3.0T angiographic imaging, T1 -weighted structural, and planning-free dual echo hypercarbic hyperoxic (i.e., carbogen) VE-ASL MRI. Vasculopathy extent, timecourses, and cerebrovascular reactivity (signal change and Z-statistic) for different VE-ASL images were contrasted across flow territories and Bonferroni-corrected P-values reported. RESULTS: BOLD cerebrovascular reactivity (i.e., long-TE VE-ASL) Z-statistics were similarly sensitive to asymmetric disease (P ≤ 0.002) regardless of labeling scenario. Cerebral blood flow reactivity correlated significantly with BOLD reactivity (Z-statistic). However, BOLD signal changes did not differ significantly between labeling scenarios (P > 0.003) or across territories (P > 0.002), indicating BOLD signal changes in response to carbogen offer low sensitivity to lateralizing disease. CONCLUSION: Dual echo VE-ASL can provide simultaneous cerebral blood flow and qualitative BOLD contrast consistent with lateralizing disease severity in patients with asymmetric steno-occlusive disease. The methodological strengths and limitations of composite BOLD and VE-ASL measurements in the clinic are discussed.

The vascular steal phenomenon is an incomplete contributor to negative cerebrovascular reactivity in patients with symptomatic intracranial stenosis.

'Vascular steal' has been proposed as a compensatory mechanism in hemodynamically compromised ischemic parenchyma. Here, independent measures of cerebral blood flow (CBF) and blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) responses to a vascular stimulus in patients with ischemic cerebrovascular disease are recorded. Symptomatic intracranial stenosis patients (n=40) underwent a multimodal 3.0T MRI protocol including structural (T1-weighted and T2-weighted fluid-attenuated inversion recovery) and hemodynamic (BOLD and CBF-weighted arterial spin labeling) functional MRI during room air and hypercarbic gas administration. CBF changes in regions demonstrating negative BOLD reactivity were recorded, as well as clinical correlates including symptomatic hemisphere by infarct and lateralizing symptoms. Fifteen out of forty participants exhibited negative BOLD reactivity. Of these, a positive relationship was found between BOLD and CBF reactivity in unaffected (stenosis degree<50%) cortex. In negative BOLD cerebrovascular reactivity regions, three patients exhibited significant (P<0.01) reductions in CBF consistent with vascular steal; six exhibited increases in CBF; and the remaining exhibited no statistical change in CBF. Secondary findings were that negative BOLD reactivity correlated with symptomatic hemisphere by lateralizing clinical symptoms and prior infarcts(s). These data support the conclusion that negative hypercarbia-induced BOLD responses, frequently assigned to vascular steal, are heterogeneous in origin with possible contributions from autoregulation and/or metabolism.

Posttreatment variables improve outcome prediction after intra-arterial therapy for acute ischemic stroke.

BACKGROUND: There are multiple clinical and radiographic factors that influence outcomes after endovascular reperfusion therapy (ERT) in acute ischemic stroke (AIS). We sought to derive and validate an outcome prediction score for AIS patients undergoing ERT based on readily available pretreatment and posttreatment factors. METHODS: The derivation cohort included 511 patients with anterior circulation AIS treated with ERT at 10 centers between September 2009 and July 2011. The prospective validation cohort included 223 patients with anterior circulation AIS treated in the North American Solitaire Acute Stroke registry. Multivariable logistic regression identified predictors of good outcome (modified Rankin score ≤2 at 3 months) in the derivation cohort; model ß coefficients were used to assign points and calculate a risk score. Discrimination was tested using C statistics with 95% confidence intervals (CIs) in the derivation and validation cohorts. Calibration was assessed using the Hosmer-Lemeshow test and plots of observed to expected outcomes. We assessed the net reclassification improvement for the derived score compared to the Totaled Health Risks in Vascular Events (THRIVE) score. Subgroup analysis in patients with pretreatment Alberta Stroke Program Early CT Score (ASPECTS) and posttreatment final infarct volume measurements was also performed to identify whether these radiographic predictors improved the model compared to simpler models. RESULTS: Good outcome was noted in 186 (36.4%) and 100 patients (44.8%) in the derivation and validation cohorts, respectively. Combining readily available pretreatment and posttreatment variables, we created a score (acronym: SNARL) based on the following parameters: symptomatic hemorrhage [2 points: none, hemorrhagic infarction (HI)1-2 or parenchymal hematoma (PH) type 1; 0 points: PH2], baseline National Institutes of Health Stroke Scale score (3 points: 0-10; 1 point: 11-20; 0 points: >20), age (2 points: <60 years; 1 point: 60-79 years; 0 points: >79 years), reperfusion (3 points: Thrombolysis In Cerebral Ischemia score 2b or 3) and location of clot (1 point: M2; 0 points: M1 or internal carotid artery). The SNARL score demonstrated good discrimination in the derivation (C statistic 0.79, 95% CI 0.75-0.83) and validation cohorts (C statistic 0.74, 95% CI 0.68-0.81) and was superior to the THRIVE score (derivation cohort: C statistic 0.65, 95% CI 0.60-0.70; validation cohort: C-statistic 0.59, 95% CI 0.52-0.67; p < 0.01 in both cohorts) but was inferior to a score that included age, ASPECTS, reperfusion status and final infarct volume (C statistic 0.86, 95% CI 0.82-0.91; p = 0.04). Compared with the THRIVE score, the SNARL score resulted in a net reclassification improvement of 34.8%. CONCLUSIONS: Among AIS patients treated with ERT, pretreatment scores such as the THRIVE score provide only fair prognostic information. Inclusion of posttreatment variables such as reperfusion and symptomatic hemorrhage greatly influences outcome and results in improved outcome prediction.

Routine clinical evaluation of cerebrovascular reserve capacity using carbogen in patients with intracranial stenosis.

BACKGROUND AND PURPOSE: A promising method for identifying hemodynamic impairment that may serve as a biomarker for stroke risk in patients with intracranial stenosis is cerebrovascular reactivity (CVR) mapping using noninvasive MRI. Here, abilities to measure CVR safely in the clinic using hypercarbic hyperoxic (carbogen) gas challenges, which increase oxygen delivery to tissue, are investigated. METHODS: In sequence with structural and angiographic imaging, blood oxygenation level-dependent carbogen-induced CVR scans were performed in patients with symptomatic intracranial stenosis (n=92) and control (n=10) volunteers, with a subgroup of patients (n=57) undergoing cerebral blood flow-weighted pseudocontinuous arterial spin labeling CVR. Subjects were stratified for 4 substudies to evaluate relationships between (1) carbogen and hypercarbic normoxic CVR in healthy tissue (n=10), (2) carbogen cerebral blood flow CVR and blood oxygenation level-dependent CVR in intracranial stenosis patients (n=57), (3) carbogen CVR and clinical measures of disease in patients with asymmetrical intracranial atherosclerotic (n=31) and moyamoya (n=29) disease, and (4) the CVR scan and immediate and longer-term complications (n=92). RESULTS: Noninvasive blood oxygenation level-dependent carbogen-induced CVR values correlate with (1) lobar hypercarbic normoxic gas stimuli in healthy tissue (R=0.92; P<0.001), (2) carbogen-induced cerebral blood flow CVR in patients with intracranial stenosis (R=0.30-0.33; P<0.012), and (3) angiographic measures of disease severity both in atherosclerotic and moyamoya patients after appropriate processing. No immediate stroke-related complications were reported in response to carbogen administration; longer-term neurological events fell within the range for expected events in this patient population. CONCLUSIONS: Carbogen-induced CVR elicited no added adverse events and provided a surrogate marker of cerebrovascular reserve consistent with intracranial vasculopathy.

Relationships between hypercarbic reactivity, cerebral blood flow, and arterial circulation times in patients with moyamoya disease.

PURPOSE: To evaluate the correlation between angiographic measures of Moyamoya disease and tissue-level impairment from measurements of tissue perfusion and cerebrovascular reactivity (CVR). MATERIALS AND METHODS: The relationship between perfusion-weighted arterial spin labeling (ASL) and hypercarbic blood oxygenation-level dependent (BOLD) CVR and time-to-peak (TTP) were compared with angiographically measured risk factors, including arterial circulation time (ACT) and modified Suzuki Score (mSS) in patients (n = 15) with Moyamoya disease. RESULTS: Hemodynamic contrasts provided information not apparent from structural or angiographic imaging. Mean z-statistics demonstrate that BOLD is significantly (P = 0.017) higher in low mSS hemispheres (z-statistic = 5.0 ± 2.5) compared with high mSS hemispheres (z-statistic = 3.7 ± 1.7), suggesting that regions with less advanced stages of Moyamoya disease have higher reactivity. After correcting for multiple comparisons, a strong trend for a direct relationship (R = 0.38; P = 0.03) between BOLD TTP and ACT was observed, and a significant inverse relationship between CBF and ACT (R = -0.47; P = 0.01) was found, demonstrating that BOLD and ASL contrasts reflect DSA measures of vascular compromise in Moyamoya disease, albeit with different sensitivity. CONCLUSION: Correlative measures between angiography and hemodynamic methods suggest that BOLD and ASL could be used for expanding the diagnostic imaging infrastructure in Moyamoya patients and potentially tracking tissue response to revascularization.

Higher volume endovascular stroke centers have faster times to treatment, higher reperfusion rates and higher rates of good clinical outcomes.

BACKGROUND AND PURPOSE: Technological advances have helped to improve the efficiency of treating patients with large vessel occlusion in acute ischemic stroke. Unfortunately, the sequence of events prior to reperfusion may lead to significant treatment delays. This study sought to determine if high-volume (HV) centers were efficient at delivery of endovascular treatment approaches. METHODS: A retrospective review was performed of nine centers to assess a series of time points from obtaining a CT scan to the end of the endovascular procedure. Demographic, radiographic and angiographic variables were assessed by multivariate analysis to determine if HV centers were more efficient at delivery of care. RESULTS: A total of 442 consecutive patients of mean age 66 ± 14 years and median NIH Stroke Scale score of 18 were studied. HV centers were more likely to treat patients after intravenous administration of tissue plasminogen activator and those transferred from outside hospitals. After adjusting for appropriate variables, HV centers had significantly lower times from CT acquisition to groin puncture (OR 0.991, 95% CI 0.989 to 0.997, p=0.001) and total procedure times (OR 0.991, 95% CI 0.986 to 0.996, p=0.001). Additionally, patients treated at HV centers were more likely to have a good clinical outcome (OR 1.86, 95% CI 1.11 to 3.10, p<0.018) and successful reperfusion (OR 1.82, 95% CI 1.16 to 2.86, p<0.008). CONCLUSIONS: Significant delays occur in treating patients with endovascular therapy in acute ischemic stroke, offering opportunities for improvements in systems of care. Ongoing prospective clinical trials can help to assess if HV centers are achieving better clinical outcomes and higher reperfusion rates.

Advanced modality imaging evaluation in acute ischemic stroke may lead to delayed endovascular reperfusion therapy without improvement in clinical outcomes.

PURPOSE: Advanced neuroimaging techniques may improve patient selection for endovascular stroke treatment but may also delay time to reperfusion. We studied the effect of advanced modality imaging with CT perfusion (CTP) or MRI compared with non-contrast CT (NCT) in a multicenter cohort. MATERIALS AND METHODS: This is a retrospective study of 10 stroke centers who select patients for endovascular treatment using institutional protocols. Approval was obtained from each institution's review board as only de-identified information was used. We collected demographic and radiographic data, selected time intervals, and outcome data. ANOVA was used to compare the groups (NCT vs CTP vs MRI). Binary logistic regression analysis was performed to determine factors associated with a good clinical outcome. RESULTS: 556 patients were analyzed. Mean age was 66 ± 15 years and median National Institutes of Health Stroke Scale score was 18 (IQR 14-22). NCT was used in 286 (51%) patients, CTP in 190 (34%) patients, and MRI in 80 (14%) patients. NCT patients had significantly lower median times to groin puncture (61 min, IQR (40-117)) compared with CTP (114 min, IQR (81-152)) or MRI (124 min, IQR (87-165)). There were no differences in clinical outcomes, hemorrhage rates, or final infarct volumes among the groups. CONCLUSIONS: The current retrospective study shows that multimodal imaging may be associated with delays in treatment without reducing hemorrhage rates or improving clinical outcomes. This exploratory analysis suggests that prospective randomised studies are warranted to support the hypothesis that advanced modality imaging is superior to NCT in improving clinical outcomes.