Virtual test occlusion for assessing ischemic tolerance using computational fluid dynamics.

Ischemic tolerance has been evaluated by the balloon test occlusion (BTO) for cerebral aneurysms and tumors that might require parent artery occlusion during surgery. However, because of its invasiveness, a non-invasive evaluation method is needed. In this study, we assessed the possibility of virtual test occlusion using computational fluid dynamics (CFD) as a non-invasive alternative to BTO for evaluating ischemic tolerance. Twenty-one patients who underwent BTO were included in the study. Virtual test occlusion was performed using CFD analysis, and the flow rate (FR) and wall shear stress (WSS) of the middle cerebral artery on the occlusion side were calculated. The correlations between these parameters and examination data including the parameters of computed tomography perfusion during BTO were assessed and the cutoff value of CFD parameters for detecting the good collateral group was calculated. The FR was strongly correlated with mean transit time (MTT) during BTO and moderately correlated with collateral flow grade based on angiographic appearance. The WSS was moderately correlated with collateral flow grade, mean stump pressure (MSP), and MTT. Furthermore, the FR and WSS were strongly correlated with the total FR and the diameters of the inlet vessels. The cutoff value of FR for detecting the good collateral group was 126.2 mL/min, while that of the WSS was 4.54 Pa. The parameters obtained through CFD analysis were correlated with collateral flow grade and MSP in addition to MTT. CFD analysis may be useful to evaluate ischemic tolerance as a non-invasive alternative to BTO.