Abstract WP79: Combination of Tmax and Relative CBV Perfusion Parameters More Accurately Predicts CTA Collaterals Than a Single Perfusion Parameter in DEFUSE 3

Abstract

Introduction: Perfusion abnormalities that have been associated with collateral status include the hypoperfusion intensity ratio (HIR) and reduction of cerebral blood volume within the ischemic lesion (CBV index). We hypothesized that assessment of both of these parameters would predict poor CTA collaterals with greater accuracy than a single parameter. This hypothesis was assessed among patients enrolled in the DEFUSE 3 trial that evaluated the efficacy of thrombectomy in patients with imaging evidence of salvageable tissue in the late 6-16 hour window. Methods: Patients were eligible for this analysis if they had adequate quality CTA and CT perfusion. An expert neuroradiologist assessed collateral status on CTA using the Tan scale. The HIR index (fraction of Tmax>10s delay within the Tmax>6s lesion) and the CBV index (mean CBV within the Tmax>6s lesion relative to normal CBV) were automatically calculated by RAPID software. ROC curve analysis was used to identify thresholds for both indices that predicted presence of poor collaterals on CTA. Proportions were compared using χ 2 and McNemar tests. Results: Of the 128 cases eligible for this analysis, 26% had poor collaterals on CTA. HIR ≥0.39 and CBV index ≤0.77 were the optimal thresholds for predicting poor collaterals on CTA. Good collaterals were present on CTA in 87% when neither of the perfusion indices were unfavorable, 77% when a single index was unfavorable, and 54% when both were unfavorable (p=0.001 for none vs both and p=0.029 for single vs both). Sensitivity for predicting poor CTA collaterals was 0.70 (95% CI 0.51-0.84) with HIR ≥0.39, 0.61 (0.42-0.77) with CBV index ≤0.77, and 0.82 (0.64-0.92) for the combined criteria of ‘either index unfavorable’ (p=0.016 for ‘either’ criteria vs CBV index alone). The presence of unfavorable criteria on both indices produced a higher specificity of 0.80 (0.70-0.87) vs. HIR alone 0.59 (0.48-0.69) or CBV alone 0.62 (0.52-0.72), both p<0.001. Conclusion: The combination of 2 fully automated perfusion parameters were more accurate for predicting CTA collaterals than a single perfusion parameter in the DEFUSE 3 population. Automated perfusion parameters do not require an expert neuroradiologist for interpretation and have no concerns regarding inter-rater agreement.