Markedly reduced apparent blood volume on bolus contrast magnetic resonance imaging as a predictor of hemorrhage after thrombolytic therapy for acute ischemic stroke

Background and Purpose - Accurate assessment of the risk of hemorrhage could help to improve patient selection for thrombolytic therapy and reduce hemorrhagic complications, especially for patients with longer or uncertain time after symptom onset. This study sought to define characteristics of hemodynamic magnetic resonance imaging (MRI), which best predict hemorrhage. Methods - Bolus contrast and diffusion MRI were performed before intravenous tissue plasminogen activator (tPA) therapy in 20 patients presenting with acute stroke symptoms within the first 6 hours after symptom onset. Hemorrhage was assessed on follow-up MRI (n=15) and computed tomography (n=5) scans. Results - Of the 20 patients studied, 5 had detectable hemorrhage on follow-up scans. Blood volume maps demonstrated virtually no signal within much of the hemorrhagic region, indicating contrast did not arrive by the end of the imaging series (80 seconds). Within the hemodynamically abnormal region, a threshold of at least 126 voxels with blood volume <5% of contralateral normal gray matter separated hemorrhagic patients from nonhemorrhagic with a sensitivity of 100% and a specificity of 73% (P<0.01). All subjects with hemorrhage were at least partially reperfused after thrombolysis, whereas most false-positives did not reperfuse (P<0.05). The number of low blood volume voxels within individual patients correlated with the number of voxels with apparent diffusion coefficient values <550×10^-6 mm²/s (P<0.019), another previously proposed predictor of hemorrhage. Conclusions - Extremely low or completely absent contrast arrival may indicate tissue-at-risk for hemorrhage before tPA treatment and thus may aid in risk-benefit assessments. Occurrence of hemorrhage within at-risk areas may depend on tissue reperfusion.