Abstract 6: Relationship Between Hypoperfusion Intensity Ratio and Ischemic Core Growth Rate is Similar on CT and MRI for Unselected Acute LVO Patients

Background: Predicting infarct growth rate (IGR) in acute stroke with large vessel occlusion (LVO) is important for treatment decision-making. IGR has typically been studied in patients treated with thrombectomy, which likely has underestimated the prevalence of ‘fast progressors’, as large core patients are less frequently treated. We aimed to study IGR in an unselected LVO population and study the association between Hypoperfusion Intensity Ratio (HIR, a surrogate marker of collaterals) and IGR as assessed by both CT and MRI. Methods: Retrospective study including ICA/M1 stroke patients with witnessed stroke onset and baseline perfusion imaging (MRI or CT) performed within 24hrs from symptoms onset. To avoid selection bias, patients were selected from (1) the registries of 3 centers with systematic use of MRI- or CT-perfusion and including both MT-treated and untreated patients, and (2) one trial where thrombectomy decisions were performed blinded from perfusion MRI results. IGR was defined as core volume/onset-to-imaging time, and fast progressors as IGR≥10mL/hr. HIR was defined as the proportion of Tmax>6s volume with Tmax>10s. Results: Overall, 423 and 215 patients were included in the MRI and CT cohorts. Median IGR was 6.4mL/hr (IQR 2.2-21.3) and 5.2mL/hr (0-25.2) in the MRI and CT cohorts, and median HIR was 0.44 (0.27-0.59) and 0.45 (0.25-0.60). 174 (41%) MRI patients and 86 (40%) CT patients were fast progressors. IGR was increasing with increase of HIR quartiles in both cohorts ( P <0.001, Figure). IGR≥10mL was found in 7%, 17%, 58%, and 83% of patients within respective increasing HIR quartiles in the MRI cohort ( P <0.001), and in 2%, 21%, 60% and 80% in the CT cohort ( P <0.001). Conclusion: In this unselected LVO population, 40% of patients were fast progressors regardless of imaging modality. HIR was a strong predictor of IGR in both CT and MRI-assessed patients, and may help for patient triage, e.g . for transfer decision from an outside hospital for thrombectomy.