Arterial spin labeling versus bolus-tracking perfusion in hyperacute stroke

Background and Purpose: Arterial spin labeling (ASL) is a perfusion magnetic resonance imaging (MRI) technique that does not require contrast administration and thus may be more practical in hyperacute stroke than susceptibility-weighted bolus-tracking perfusion-weighted imaging (PWI). However, a threshold for ASL measurement of the ischemic penumbra needs to be determined. Methods: A total of 58 patients with acute hemispheric ischemic stroke were imaged within 6 hours of symptom onset with MRI including ASL, diffusion-weighted MRI (DWI), and PWI, after perfusion computed tomography (CTP). Patients had repeat MRI at 24 hours. On repeat imaging, 32 patients did not reperfuse and were used to determine the penumbra threshold. A receiver-operating curve and a volumetric analysis were undertaken to identify the ASL-cerebral blood flow (CBF) threshold for the acute penumbra compared with the 24-hour DWI lesion in patients without reperfusion and with the acute PWI and CTP-Tmax thresholds. Results: An ASL-CBF threshold of 40% showed the highest area under the curve (AUC) for detection of the acute penumbra, defined by 24-hour DWI in nonreperfused patients (AUC 0.76, 95% confidence interval, 0.63-0.85), and was also accurate compared with the acute PWI-Tmax+6 seconds penumbral threshold (AUC 0.79, 95% confidence interval, 73-84) and acute CTP-Tmax 5.5 seconds penumbral threshold (AUC 0.77, 95% confidence interval, 72-84). Using a perfusion-to-diffusion mismatch ratio of 1.8:1, an ASL-CBF 40% mismatch compared with PWI-Tmax+ 6 seconds-DWI and CTP mismatch showed good sensitivity (0.81) and specificity (0.71). Conclusions: ASL-DWI mismatch shows potential to identify salvageable tissue in hyperacute stroke