MRIを用いた脳動脈瘤血流動態解析  [in Japanese] MRI-based Flow Dynamics Analysis in Patients with Cerebral Aneurysm  [in Japanese]

脳動脈瘤患者にMRIを用いた血流動態解析を行い,術中所見と比較検討した.血流動態解析はtwo dimensional fast card phase contrast(2D-PC)法を用いて心電図同期下に撮像し,得られたデータを血流動態解析ソフトウェアを用いて解析した.術前に血流動態解析を行った未破裂脳動脈瘤5例(中大脳動脈瘤3例,前交通動脈瘤2例),破裂前交通動脈瘤1例,計6例に開頭クリッピング術を行った.術中所見では全例で動脈瘤壁の一部菲薄化を認め,同部位は術前の血流動態解析上,剪断応力は生理的範囲より低かった.しかし,1例では複数ヵ所で菲薄化し,剪断応力は低値から高値を示した.本法を用いることで,破裂脳動脈瘤においては破裂点の推定,未破裂脳動脈瘤においては将来の破裂の危険性や経過観察中の増大・形状の変化などの自然歴を推測するために有用である可能性が示唆された.また本法は,従来の脳血管造影検査に基づく方法に比べ簡便かつ非侵襲的であるため,施行可能である.今後も症例を重ね検討を行う必要があると考えられた.

Object: Flow dynamics are considered to have profound effects on the development and rupture of cerebral aneurysms. The present study used magnetic resonance imaging (MRI)-based flow dynamics analysis to investigate patients with cerebral aneurysms using 4 dimensional analysis (3 geometrical dimensions+chronological changes) to compare the findings of flow dynamics analysis with the intraoperative findings. Methods: MRI-based flow dynamics analysis was performed preoperatively in 6 patients with cerebral aneurysms, 3 with middle cerebral artery aneurysm and 3 with anterior communicating artery aneurysm. Flow dynamics data collection was carried out by the two dimensional fast card phase contrast method with a conventional MRI scanner (GE Signa 1.5 Tesla), combined with ECG gating. The data was analyzed using commercially available software (Flow visualization and analysis: Flova, Artech). Wall shear stress (WSS) was calculated and its change related to cardiac cycle was obtained as a color map. The preoperative findings were directly compared to the intraoperative findings. Results: Intraoperative findings showed that all aneurysms had areas of thin walls which were exposed to low levels of WSS. However, 1 of the 6 patients had multiple thin-wall areas in one aneurysm, one of which was exposed to low levels of WSS and the others to high levels of WSS. Quantification of WSS was available in 2 cases, which showed the thin-wall lesion was exposed to low WSS (around 1.0Pa) and the thick-wall lesion was exposed to high WSS (over 3.0Pa). Conclusion: MRI-based flow dynamics analysis is less invasive for patients and easy to perform. For better understanding of the natural history and risk of rupture of cerebral aneurysms, further study is needed.