BACKGROUND AND PURPOSE Cerebrovascular collaterals have been increasingly recognized as predictive of clinical outcomes in Moyamoya disease in Asia. The aim of this study was to characterize collaterals in North American adult patients with Moyamoya disease and to assess whether similar correlations are valid. MATERIALS AND METHODS Patients with Moyamoya disease (n = 39; mean age, 43.5±10.6 years) and age- and sex-matched control subjects (n = 33; mean age, 44.3±12.0 years) were graded via angiography. Clinical symptoms of stroke or hemorrhage were graded separately by imaging. Correlations between collateralization and disease severity, measured by the modified Suzuki score, were evaluated in patients with Moyamoya disease by fitting a regression model with clustered ordinal multinomial responses. RESULTS The presence of leptomeningeal collaterals (P = .008), dilation of the anterior choroidal artery (P = .01), and the posterior communicating artery/ICA ratio (P = .004) all correlated significantly with disease severity. The presence of infarct or hemorrhage and posterior steno-occlusive disease did not correlate significantly with the modified Suzuki score (P=.1). Anterior choroidal artery changes were not specific for hemorrhage. Patients with Moyamoya disease were statistically more likely than controls to have higher posterior communicating artery/ICA ratios and a greater incidence of leptomeningeal collaterals. CONCLUSIONS As with Moyamoya disease in Asian patients, the presence of cerebrovascular collaterals correlated with the modified Suzuki score for disease severity in North American patients with Moyamoya disease. However, anterior choroidal artery changes, which correlated with increased rates of hemorrhage in Asian studies, were not specific to hemorrhage in North Americans.

Background and Purpose The importance of collateralization for maintaining adequate cerebral perfusion is increasingly recognized. However, measuring collateral flow noninvasively has proved elusive. The aim of this study was to assess correlations among (1) baseline perfusion and arterial transit time artifact, (2) cerebrovascular reactivity (CVR), and (3) the presence of collateral vessels on digital subtraction angiography (DSA). Materials and Methods The relationship between the presence of collateral vessels on arterial-spin-labeling (ASL) MRI and DSA was compared to blood-oxygenation-level-dependent (BOLD) MRI measures of hypercapnic cerebrovascular reactivity (CVR) in patients with symptomatic intracranial stenosis (n=18). DSA maps were reviewed by a neuroradiologist and assigned the following scores: 1) collaterals to the periphery of the ischemic site; 2) complete irrigation of the ischemic bed via collateral flow; 3) normal antegrade flow. ASL maps were scored according to 0) low signal; 1) moderate signal with arterial transit artifact (ATA); 2) high signal with ATA; 3) normal signal. Results In regions with normal-to-high signal on ASL, collateral vessel presence on DSA strongly correlated with declines in CVR as measured on BOLD MRI (p<0.001), most notably in patients with non-atherosclerotic disease. There was a trend toward increasing CVR with increases in the degree of collateralization on DSA (p=0.082). Conclusion Collateral vessels may have fundamentally different vasoreactivity properties than healthy vessels, a finding that is observed most prominently in non-atherosclerotic disease and to a lesser extent in atherosclerotic disease.

'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 ¼ 40) underwent a multimodal 3.0T MRI protocol including structural (T 1 -weighted and T 2 -weighted fluidattenuated 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 degreeo50%) cortex. In negative BOLD cerebrovascular reactivity regions, three patients exhibited significant (Po0.01) 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.

Cerebrovascular reactivity (CVR)-weighted blood-oxygenation-level-dependent magnetic resonance imaging (BOLD-MRI) experiments are frequently used in conjunction with hyperoxia. Owing to complex interactions between hyperoxia and hypercapnia, quantitative effects of these gas mixtures on BOLD responses, blood and tissue R2*, and blood oxygenation are incompletely understood. Here we performed BOLD imaging (3 T; TE/TR=35/2,000 ms; spatial resolution=3 × 3 × 3.5 mm(3)) in healthy volunteers (n=12; age=29±4.1 years) breathing (i) room air (RA), (ii) normocapnic-hyperoxia (95% O2/5% N2, HO), (iii) hypercapnic-normoxia (5% CO2/21% O2/74% N2, HC-NO), and (iv) hypercapnic-hyperoxia (5% CO2/95% O2, HC-HO). For HC-HO, experiments were performed with separate RA and HO baselines to control for changes in O2. T2-relaxation-under-spin-tagging MRI was used to calculate basal venous oxygenation. Signal changes were quantified and established hemodynamic models were applied to quantify vasoactive blood oxygenation, blood-water R2*, and tissue-water R2*. In the cortex, fractional BOLD changes (stimulus/baseline) were HO/RA=0.011±0.007; HC-NO/RA=0.014±0.004; HC-HO/HO=0.020±0.008; and HC-HO/RA=0.035±0.010; for the measured basal venous oxygenation level of 0.632, this led to venous blood oxygenation levels of 0.660 (HO), 0.665 (HC-NO), and 0.712 (HC-HO). Interleaving a HC-HO stimulus with HO baseline provided a smaller but significantly elevated BOLD response compared with a HC-NO stimulus. Results provide an outline for how blood oxygenation differs for several gas stimuli and provides quantitative information on how hypercapnic BOLD CVR and R2* are altered during hyperoxia.

Background and Purpose Crossed cerebellar diaschisis (CCD) is most commonly investigated using hemodynamic PET and SPECT imaging. However, noninvasive MRI offers advantages of improved spatial resolution, allowing hemodynamic changes to be compared directly with structural findings and without concerns related to ionizing radiation exposure. The aim of this study was to evaluate relationships between CCD identified from cerebral blood flow (CBF)-weighted arterial spin labeling (ASL) MRI with cerebrovascular reactivity (CVR)-weighted blood oxygenation level dependent (BOLD) MRI, Wallerian degeneration, clinical motor impairment, and corticospinal tract involvement. Methods Subjects (n=74) enrolled in an ongoing observational stroke trial underwent CBF-weighted ASL and hypercapnic CVR-weighted BOLD MRI. Hemispheric asymmetry indices for basal cerebellar CBF, cerebellar CVR, and cerebral peduncular area were compared between subjects with unilateral supratentorial infarcts (n=18) and control subjects without infarcts (n=16). CCD required (1) supratentorial infarct and (2) asymmetric cerebellar CBF (>95% confidence interval relative to controls). Results In CCD subjects (n=9), CVR (p=0.04) and cerebral peduncular area (p < 0.01) were significantly asymmetric compared to controls. Compared to infarct subjects not meeting CCD criteria (n=9), CCD subjects had no difference in corticospinal tract location for infarct (p=1.0) or motor impairment (p=0.08). Conclusions CCD correlated with cerebellar CVR asymmetry and Wallerian degeneration. These findings suggest that noninvasive MRI may be a useful alternative to PET or SPECT to study structural correlates and clinical consequences of CCD following supratentorial stroke.