Optimal Cerebral Blood Flow Thresholds for Ischemic Core Estimation Using Computed Tomography Perfusion and Diffusion‐Weighted Imaging

Objective Computed tomography perfusion (CTP) imaging is crucial in quantifying cerebral blood flow (CBF) and thereby making an endovascular treatment (EVT) after large vessel occlusion. However, CTP is prone to overestimating the ischemic core. We sought to delineate the optimal regional CBF (rCBF) thresholds of pre‐EVT CTP. Methods We collected acute ischemic stroke patients due to large vessel occlusion who achieved successful recanalization with baseline CTP, immediate post‐EVT diffusion‐weighted image (DWI) within 3 hours, and delayed post‐EVT DWI between 24 and 196 hours. Core volumes estimated by CTP at various rCBF thresholds were validated against immediate and delayed DWI lesion volumes. Results A total of 175 acute large vessel occlusion patients were included. Baseline CTP was taken in a median of 24 minutes (interquartile range [IQR] 21–31 minutes) after arrival; after the CTP, groin puncture in a median of 37 minutes (IQR 28–52 minutes), immediate post‐EVT DWI scans in a median of 1.6 hours (IQR 0.8–2.1 hours), and delayed DWI scans in a median of 89 hours (IQR 69–106 hours). The correlations between the rCBF thresholds were the best at rCBF <22% for immediate DWI (0.64; 95% CI 0.55–0.73) and at rCBF <30% for delayed DWI (0.69; 95% CI 0.61–0.76). The interval between CTP and recanalization was inversely correlated with the overestimation of ischemic core volume compared with the subsequent DWI. Interpretation Optimal rCBF thresholds for estimating ischemic core using CTP depend significantly on the timing of DWI post‐EVT and CTP to recanalization delay. The optimal rCBF thresholds for ischemic core estimation may vary depending on the clinical setting. ANN NEUROL 2025;97:919–929