Identification of the optimal thresholds for the hypoperfusion intensity ratio in moyamoya disease

OBJECTIVE The authors’ objective was to retrospectively compare two methods for defining the hypoperfusion intensity ratio (HIR) in moyamoya disease (MMD) by using hypoperfused volumes calculated from time to maximum of the residue function (Tmax) thresholds of 10 seconds/4 seconds and 10 seconds/6 seconds. METHODS All hemispheres were categorized into normal, ischemic, and hemorrhagic groups. Hypoperfused volumes were calculated using Tmax thresholds of 10 seconds, 6 seconds, and 4 seconds. HIR was computed as Tmax > 10 seconds/Tmax > 4 seconds (HIR 10/4 ) and Tmax > 10 seconds/Tmax > 6 seconds (HIR 10/6 ). Angiographic collaterals were assessed using CT perfusion (CTP)–sourced images (CTP-sis). The 3-month clinical follow-up included primary outcomes (survival or death) and secondary outcomes (modified Rankin Scale [mRS] and Katz activities of daily living [ADL] scale scores). Multivariate logistic regression and correlation analyses were conducted. RESULTS Thirty patients (54 hemispheres) were included. Patients with poor primary outcomes exhibited higher rates of hypertension (p = 0.015), larger hypoperfused volumes, and elevated HIR 10/4 and HIR 10/6 (p < 0.001). The regression model with HIR 10/4 outperformed that with HIR 10/6 for predicting primary outcomes (Z = 2.02, p = 0.044). Both HIR 10/4 and HIR 10/6 correlated with mRS and ADL scores (p < 0.05). Although there was no correlation between HIR and CTP-sis when all hemispheres were included, a significant association was found between HIR 10/4 and CTP-sis when hemispheres with hemorrhagic lesions were excluded (p = 0.013). CONCLUSIONS HIR 10/4 exhibited a superior predictive value for primary outcomes in MMD compared to HIR 10/6 . Additionally, HIR 10/4 showed a significant association with angiographic collaterals, particularly in ischemic MMD cases. This study suggested that HIR defined as Tmax > 10 seconds/Tmax > 4 seconds may be more suitable than Tmax > 10 seconds/Tmax > 6 seconds in MMD.