CT colonography―大腸癌スクリーニングへの応用を目指した画像処理法の開発

Development of CT Colonography as a Screening Tool for Colorectal Cancer

要旨　CT colonographyは大腸の画像診断法として，欧米ばかりでなくわが国においても広く認知され，具体的な臨床診断へ導入されるようになった．最近では術前診断のみならず，大腸癌スクリーニングへ導入する施設が増加しており，一般的な大腸検査法としての地位を確実に築きつつある．デジタルCT画像のメリットを生かし，従来の消化管診断からは予想不可能な大腸の画像表示方法が開発され，実際の臨床診断に応用されるに至った．これまで研究されてきたコンピュータ支援検出，tagging前処置やelectronic cleansingの精度も向上し，画期的な新しい大腸の画像診断システムが構築されている．関連各社から様々な画像処理アルゴリズムを搭載した新しい画像ワークステーションが次々と登場し，フルデジタル画像処理による大腸CT三次元診断が現実のものとなった．既にCT colonographyによる大腸癌スクリーニングは世界的な傾向となり，今後，わが国の大腸内視鏡診断における経験を生かすことにより，真に有効性のあるCTC診断システムが構築されていくと予想される．

　Recently, CTC（CT colonography）has become an effective tool for colorectal cancer screening not only in western countries but in Japan. Many hospitals have introduced CTC into preoperative staging and colorectal screening. CTC has established its status as a diagnostic tool in colorectal examinations. By processing 3D digital volume data from multi-slice CT helical scanning, various kinds of three-dimensional images can be acquired to visualize the colorectum. Virtual endoscopy, volume rendering image, MPR（multi-planar reconstruction）, and their combination views are very useful for diagnosing colorectal lesions accurately. As a screening CTC image, VGP（virtual gross pathology）has been developed to visualize the entire mucosal surface of colorectum. VGP is useful for screening colorectal lesions efficiently in a short time. Computer-aided detection and digital preparation systems have also been improved, and are now available for CTC screening with VGP. CT manufacturers and workstation vendors are working hard to develop more effective CTC imaging systems, including new image analyses to enhance CTC diagnostic ability. Colorectal screening with CTC is now a common concept all over the world, and is paving an innovative way to a fully digitalized diagnostic system in colorectal diagnosis. With the use of superb Japanese experience in gastrointestinal tract diagnosis, CTC made in Japan will be the most reliable diagnostic system for colorectal screening in the world.