画像処理法による良性胃潰瘍と陥凹型早期胃癌の鑑別診断―Ⅲ型を意識して

Differential Diagnosis between Benign Gastric Ulcer and Depressed-type Early Gastric Cancer by an Image Processing Method: Focusing on Type Ⅲ

要旨　電子内視鏡（TGS-50B）と画像解析装置を用いて良性胃潰瘍と早期胃癌の鑑別点をⅢ型早期胃癌を意識しつつ検討した．以前から筆者らは良性胃潰瘍の経過を電子内視鏡で詳細に観察し，潰瘍辺縁にみられる索状の再生粘膜を鮮明に捉えている．今回，潰瘍辺縁の再生粘膜模様に着目して陥凹型早期胃癌との鑑別を試みた．良性胃潰瘍では治癒過程期において潰瘍辺縁にOSF値の高い索状の再生粘膜が全周にわたり認められた．一方，癌病巣内の消化性潰瘍においては再生粘膜模様がないか，あっても一部に欠損像がみられた．すなわち，再生粘膜模様に留意することによって陥凹性早期胃癌の診断向上が期待できる．

　Endoscopic diagnosis has been nearly perfected and diagnostic problems are rarely encountered in the great majority of patients. Nevertheless, there are occasions when cancer may be mistaken for an ulcer or an ulcer easily confused with a cancer.

　It was difficult to differentiate between the redness of regenerating mucosa at the edge of an ulcer and the redness of a cancer lesion using a conventional fiberscope. But it is easy to distinguish between the regenerating mucosal pattern of an ulcer and the uneven punctate redness of a cancer with an electronic endoscope which provides a fine resolvable image. With this in mind, we attempted to differentiate between depressed-type early gastric cancer and benign gastric ulcer using an electronic endoscope (TGS-50B;Toshiba-Machida) and an image analyzer (SPICCA;JapanAVIONICS).

　We observed ulcerative lesions in detail with the electronic endoscope, and used the image analyzer to convert the redness surrounding the ulcer into binary digitized data. Next, the binary digitized pattern was separated into minimum units of gastric mucosal pits, an oval was postulated which possessed an inertial moment identical to each of the particles, and calculating its oval specification (OSF) value as th eratio of its long diameter to its short diameter, we used the average value of 20 particles as the image value.

　Evaluating the results of differential diagnosis of benign gastric ulcer and cancer-associated ulcer based on the OSF values obtained by image analysis gave the following results :

　(1) During the healing process, high OSF value in the entire periphery of the ulcer and a long, neat, string-like regenerating mucosal pattern indicate a benign ulcer.

　(2) The absence of a neat, string-like regenerating mucosal pattern in a portion of the margin of a gastric ulcer indicates that a malignant lesion should be suspected at that site.