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Purpose: Identifying acute ischemic stroke (AIS) patients with impending parenchymal hematoma (PH) after thrombolysis and/or endovascular treatments would be useful in guiding following treatment strategies.Methods: 102 patients had MRI on Siemens 1.5 T Avanto or 3.0 T TIM Trio systems, using 12 channel head coils. A pseudo-continuous ASL pulse sequence with background suppressed 3D GRASE readout was applied along with other MR sequences within 24 hours after treatment with the following parameters: TR/TE/label time/post-labeling delay (PLD), 4000/22/1500/2000 ms; 30 pairs of label and control images with a scan time of 4min. Infarction core was acquired using ADC value < 550х10–6 mm2/s. CBF within the infarction core and its contralateral counterpart was measured. CBF at the 25th, median and 75th percentiles in the contralateral part were used as thresholds to define reperfusion in the lesion. ASL reperfusion volume above the threshold was calculated and noted as vol-25, vol-50 and vol-75 respectively.Results: Both ADC threshold volume and ASL reperfusion volume at all three percentiles differed significantly between HT categories such as HT vs. no HT, HI vs. PH, PH vs. no PH and PH-2 vs. no PH-2. In the ROC analysis, ASL reperfusion vol-25 has the highest area under the curve (AUC) (Figure 1). ASL vol-25 had significantly higher AUC when compared with ADC threshold volume in prediction of PH (0.782 vs. 0.679, P=0.002) and in prediction of PH-2 (0.844 vs. 0.749, P=0.0027). In stepwise multivariate logistic regression analysis, only ASL reperfusion vol-25 emerged as an independent predictor of HT (OR=1.94, 95% CI 1.14-3.59, P=0.022). Similarly for the PH2 vs. no PH2 outcome, only ASL reperfusion vol-25 was an independent predictor (OR=2.34, 95% CI 1.22-5.28, P=0.02).Conclusion: Post treatment MRI-ASL can evaluate reperfusion status in AIS patients. Increasing volume of reperfusion within infarction core is highly associated with impending higher grade of HT.