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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

[Fundamental study of the energy subtraction process using a monochromatic image for computed tomography angiography after coil embolization of a cerebral aneurysm].

Coil-embolized cerebral aneurysms are difficult to evaluate using computed tomography (CT) angiography (CTA) due to artifacts caused by the coil devices. This study was conducted to assess the practicality of energy subtraction processing using monochromatic images obtained using CTA after coil embolization of a cerebral aneurysm. In this study, the changes in the CT value of the contrast agent and the coil were analyzed not only at varying monochromatic energy levels but also by energy subtraction processing. Our analyses revealed an exponential change in the CT value of the contrast agent at any desired energy. We also found that the CT value of the coil was unchanged at the upper threshold of the grayscale limit. Based on these results, we were able to create images of changes in material-specific CT values and thus eliminate the material. Energy subtraction processing enabled us to distinguish between the contrast agent, the coil, and the artifacts from coil devices. We suggest that energy subtraction processing using monochromatic images can resolve the limitations of CTA after coil embolization of cerebral aneurysms.