Magnetic resonance perfusion imaging in acute ischemic stroke using continuous arterial spin labeling

Background and Purpose-Continuous arterial spin-labeled perfusion MRI (CASL -PI) uses electromagnetically labeled arterial blood water as a diffusible tracer to noninvasively measure cerebral blood now (CBF), We hypothesized t hat CASL-PI could detect perfusion deficits and perfusion/diffusion mismatc hes and predict outcome in acute ischemic stroke. Methods-We studied 15 patients with acute ischemic stroke within 24 hours o f symptom onset. With the use of a 6-minute imaging protocol, CASL-PI was m easured at 1.5 T in 8-mm contiguous supratentorial slices with a 3.75-mm in -plane resolution. Diffusion-weighted images were also obtained. Visual ins pection for perfusion deficits, perfusion/diffusion mismatches, and effects of delayed arterial transit was performed. CBF in predetermined vascular t erritories was quantified by transformation into Talairach space. Regional CBF values were correlated with National Institutes of Health Stroke Scale (NIHSS) score on admission and Rankin Scale (RS) score at 30 days. Results-Interpretable CASL-PI images were obtained in all patients. Perfusi on deficits were consistent with symptoms and/or diffusion-weighted imaging abnormalities. Eleven patients had hypoperfusion, 3 had normal perfusion, and 1 had relative hyperperfusion. Perfusion/diffusion mismatches were pres ent in 8 patients. Delayed arterial transit effect was present in 7 patient s; serial imaging in 2 of them showed that the delayed arterial transit are a did not succumb to infarction. CBF in the affected hemisphere correlated with NIHSS and RS scores (P=0.037 and P=0.003, Spearman rank correlation). The interhemispheric percent difference in middle cerebral artery CBF corre lated with NIHSS and RS scores (P=0.007 and P=0.0002, respectively). Conclusions-CASL-PI provides rapid noninvasive multislice imaging in acute ischemic stroke. It depicts perfusion deficits and perfusion/diffusion mism atches and quantifies regional CBF, CASL-PI CBF asymmetries correlate with severity and outcome, Delayed arterial transit effects may indicate collate ral flow.