Among the 74 patients, pretreatment PWI was available in 72/74 (97%) and technically adequate slope imaging in 69/74 (93%). Post-treatment PWI was available in 71/74 (96%) with slope imaging in 70/74 (95%). Among the 69 patients with pretreatment slope imaging, parenchymal hematomas occurred in 7 (10%), including PH2 in 2 and PH1 in 5, and hemorrhagic infarctions in 11 (16%), including HI2 in 9 and HI1 in 2. Pretreatment slope imaging revealed permeability abnormalities in 6 patients (9%), of whom 5 developed hemorrhages, including PH2 in 2, PH1 in 1, and HI2 in 2. Pretreatment permeability abnormality increased the odds of a parenchymal hematoma, OR 14.8, 95% CI 2.2–98.0, p0.007.Pretreatment delayed contrast arrival was noted in 4 cases, among whom 1 patient experienced PH1 and 3 fatal outcome. On post-treatment slope imaging, permeability abnormality was evident in 11 cases, and all experienced hemorrhagic transformation. Delayed contrast arrival was present in 6, associated with HT in 1 and fatal outcome in another 3. In conclusion, analysis of the DEFUSE cohort confirms the feasibility and predictive value of pretreatment slope imaging of permeability abnormality. Permeability derangements increased the odds of parenchymal hematoma after lytic therapy 15-fold. Permeability abnormality on post-treatment MRI correlated even more strongly with hemorrhage. Another form of slope imaging abnormality, delayed contrast arrival, may be an additional useful predictor of poor outcome.