Abstract Number ‐ 57: Investigation on Hemodynamic Force Related to Thin‐walled Regions in Intracranial Aneurysm by Using CFD
Authors: Masuda Kazunori , Kakizaki Shota , Nagayama Gota , Kato Naoki , Takao Hiroyuki , Fujimura Soichiro , Sunami Shota , Kasai Tomoki , Yuzawa Kazuya , Uchikawa Hayato , Ishibashi Toshihiro , Fukudome Koji , Yamamoto Makoto , Murayama Yuichi 
Published: April 2023

Introduction
Although thin‐walled regions (TWRs) in an intracranial aneurysm have a risk of rupture due to contact with surgical instruments, imaging modalities cannot accurately evaluate the thickness of aneurysm walls. The surgical operation will be able to perform safely by identifying the location of TWRs before the treatment. In previous studies, computational fluid dynamics (CFD) has been used to investigate the relationship between hemodynamics and TWRs. However, a quantitative method has not been employed to evaluate the location of TWRs. This study aims to clarify the relationship between hemodynamics and TWRs by comparing the results of CFD analysis with quantitatively defined TWRs.

Methods
We identified 70 aneurysms (MCA: 48, ACA: 20, ICA: 2) treated with craniotomy and clipping. CFD analysis was conducted to evaluate the pressure difference (PD), wall shear stress (WSS), and wall shear stress divergence (WSSD) on the aneurysm wall. High regions were defined as the regions with values above the 90th percentile for each parameter, and Low regions were defined as the regions with values below the 10th percentile for each parameter. In this study, 4 regions (HighPD, HighWSS, LowWSS, and HighWSSD) and 6 regions obtained by combining two of these regions were defined as regions of interest (RoI). Because TWRs generally indicate intense red, the comprehensive red value (cR value) was defined by using the RGB color model to evaluate the intensity of redness. The cR value was calculated for each pixel of the intraoperative images, and TWRs were defined using the cR value. Comparing the results of CFD analysis and identified TWRs, the percentage of the area of TWRs in RoI was calculated as the occupancy ratio.

Results
Table 1 shows the mean occupancy ratio for each defined RoI. The mean occupancy ratio in RoI by a single parameter is higher in the order of HighPD, HighWSSD, HighWSS, and LowWSS regions. In HighPD regions, which show the highest occupancy ratio, the impingement flow to the aneurysm wall is considered to make the aneurysm wall thinner. In HighWSSD regions, the aneurysm wall seems to have thinned due to the tensile force along the wall surface caused by blood flow. The mean occupancy ratio of RoI obtained by the combination of two regions is lower than that of HighPD regions. However, in some cases, TWRs that could not be identified by HighPD regions can be detected by HighPD or HighWSSD regions.

Conclusions
The mean occupancy ratio for RoI was higher in the order of HighPD, HighWSSD, HighWSS, and LowWSS regions. Therefore, it was suggested that these hemodynamic parameters are related to TWRs. Furthermore, in some cases, TWRs that the RoI of a single parameter could not identify can be detected using RoI obtained by the combination of two parameters.