Three-dimensional CT angiography（3D-CTA）による破裂・未破裂脳動脈瘤の診断

Diagnosis of Ruptured and Unruptured Cerebral Aneurysms with Three-dimensional CT Angiography (3D-CTA)

I．はじめに

　近年computer imagingの発達により3次元画像が作製され，病変の局在診断や治療計画の検討に応用されているが，1989年に登場した高速螺旋型CTは従来のCTでは困難であった3次元画像の作製を容易にした．

　1992年より連続回転型高速CT装置が札幌医科大学に導入され，短時間に広範囲の部位が撮影されるようになり，良好な3次元画像や多断画再構成画像（MPR image）が作製可能となった．その後ソフトウエアーの開発で3次元CT angiography（3D-CTA）が検査可能となり，脳血管障害の診断に3D-CTAを使用してきたが，本論文では破裂および未破裂脳動脈瘤の診断に使用した結果について報告する．

Three-dimensional CT angiography (3D-CTA) is a new, minimally invasive technique for the diagnosis of cerebral aneurysms. The purpose of this study is to compare the diagnostic value of 3D-CTA for ruptured and unruptured cerebral aneurysms with that of MR angiography (MRA) and digital subtraction angiogra-phy (DSA).

Forty-one cases consisting of 11 cases of ruptured aneurysms and 30 cases of unruptured aneurysms, with a total of 67 cerebral aneurysms, were included in this study.

3D-CTA was performed with a bolus injection of nonionic contrast medium on the SOMATOM PLUS-S scanner and the ProSeed Accell scanner. Three-dimensional images were obtained by both shaded sur-face reconstruction (SSR) method and maximum in-tensity projection (MIP) method.

The CT values of cisternal clot in cases of ruptured cerebral aneurysms did not exceed 90HU in any of the cases. The effect of SAH was, therefore, eliminated in the SSR images through a threshold level processing of a CT value of 150HU. All the cerebral aneurysms were visualized by this process. With regard to the detectability of cerebral aneu-rysms, 3D-CTA was able to demonstrate cerebral aneurysms with diameters of larger than 1mm as well as giant aneurysms which MRA would sometimes fail to reveal.

3D-CTA was superior to MRA and DSA in making diagnosis of small aneurysms such as those with dia-meters of less than 3mm. There was no difference be-tween 3D-CTA and DSA in diagnostic ability for medium-sized aneurysms. With regard to large aneurysms of more than 12mm in diameter, 3D-CTA was considered to be more useful than MRA and DSA, particularly for planning of operations by its feasibility for marking a simulation. For the operation, three-dimensional images of 3D-CTA provided useful in-formation concerning the shape and anatomical features relating to the aneurysm, particularly the parent arter-ies and bony structures.

The aneurysms located in the vicinity of the caver-nous sinus were able to be visualized by 3D image re-construction with elevation of the threshold level to 250HU. In addition, MIP image was able to visualize the calcification of an arterial wall, which provided use-ful information for applying clips for aneurysms.