3D MR Cisternography/Angiography Fusion Imagingによる血管外壁形態からみた内頸動脈－後交通動脈瘤とInfundibular Dilationの鑑別診断

Fusion Imaging of 3D MR Cisternography/Angiography for Differential Diagnosis of Internal Carotid-Posterior Communicating Artery Aneurysms and Infundibular Dilations

Ⅰ．は じ め に

　Magnetic resonance angiography（MRA）による脳血管病変のスクリーニングが普及するに伴い，無症候性未破裂脳動脈瘤が検出される機会が増えている．そのなかで内頸動脈－後交通動脈分岐部に脳動脈瘤様の血管膨隆部が認められ，脳動脈瘤，infundibular dilation，あるいは正常な動脈起始部との鑑別診断に苦慮する場合も多い^1-4)．今回3D MR cisternography（MRC）と3D MRAの融合画像（3D MRC/MRA fusion image^7,9)）を作成して，血管外壁形態から血管膨隆部を鑑別したので，その画像解析技術につき報告する．

By using a fusion imaging of three-dimensional (3D) magnetic resonance cisternography (MRC) and coregistered magnetic resonance angiography (MRA),protrusions at the bifurcation of the internal carotid-posterior communication artery,detected by MRA,were investigated to differentiate between the infundibular dilations and aneurysms. The MRA,obtained by the 3D time-of-flight sequence,showed the flow-related arterial structures by means of an inflow effect mainly induced by the peak systolic flow velocity. The MRC,obtained by 3D fast spin-echo sequence,depicted the contours of the vascular structures within the cisternal space in contrast to the surrounding cerebrospinal fluid. Fusion images of 3D MRC/MRA showed the anatomy of protrusions from the different viewpoints with flow-related intraluminal images (MRA) in conjunction with outer-wall configuration images of the vascular structures (MRC). This imaging technique may be useful to differentiate the infundibular dilations from the internal carotid-posterior communicating artery aneurysms.