AbstractBackground and PurposeQuantitative CT perfusion (CTP) thresholds for assessing the extent of ischemia in patients with acute ischemic stroke (AIS) have been established; relative cerebral blood flow (rCBF) <30% is typically used for estimating estimated ischemic core volume and T_max (time to maximum) >6 seconds for critical hypoperfused volume in AIS patients with large vessel occlusion (LVO). In this study, we aimed to identify the optimal threshold values for patients presenting with AIS secondary to distal medium vessel occlusions (DMVOs).MethodsIn this retrospective study, consecutive AIS patients with anterior circulation DMVO who underwent pretreatment CTP and follow‐up MRI/CT were included. The CTP data were processed by RAPID (iSchemaView, Menlo Park, CA) to generate estimated ischemic core volumes using rCBF <20%, <30%, <34%, and <38% and critical hypoperfused volumes using T_max (seconds) >4, >6, >8, and >10. Final infarct volumes (FIVs) were obtained from follow‐up MRI/CT within 5 days of symptom onset. Diagnostic performance between CTP thresholds and FIV was assessed in the successfully and unsuccessfully recanalized groups.ResultsFifty‐five patients met our inclusion criteria (32 female [58.2%], 68.0 ± 12.1 years old [mean ± SD]). Recanalization was attempted with intravenous tissue‐type plasminogen activator and mechanical thrombectomy in 27.7% and 38.1% of patients, respectively. Twenty‐five patients (45.4%) were successfully recanalized. In the successfully recanalized patients, no CTP threshold significantly outperformed what is used in LVO setting (rCBF < 30%). All rCBF CTP thresholds demonstrated fair diagnostic performances for predicting FIV. In unsuccessfully recanalized patients, all T_max CTP thresholds strongly predicted FIV with relative superiority of T_max >10 seconds (area under the receiver operating characteristic curve = .875, p = .001).ConclusionIn AIS patients with DMVOs, longer T_max delays than T_max > 6 seconds, most notably, T_max > 10 seconds, best predict FIV in unsuccessfully recanalized patients. No CTP threshold reliably predicts FIV in the successfully recanalized group nor significantly outperformed rCBF < 30%.