AFI

Autofluorescence Imaging for Screening Colonoscopy

要旨　自家蛍光内視鏡（AFI）は，消化管粘膜への励起光の照射により内因性の蛍光物質から生じる自家蛍光をとらえて画像化する装置である．現行のAFI systemは，白色光観察からボタン1つでAFI観察に切り替え可能である．AFI観察では大腸腫瘍は緑色の背景に紫色に描出され，特に平坦な病変の拾い上げ診断能の向上が期待されている．現在までの検討では，右半結腸において白色光観察に比べて見逃し割合の低下が示されたものの，S状結腸においてはその有用性が示されなかった．管腔が狭く屈曲の多いS状結腸ではAFIの機能を十分に発揮できない可能性があるため，筆者らは先端に透明フードを装着した観察法を用い，その有用性について検討している．

　AFI（autofluorescence imaging）is an endoscopic device to visualize the reflected autofluorescence which is emitted from endogeneous fluorophore by exposing short wavelength excitation light. The latest model of the AFI system can switch the observation mode in a few seconds─white light image（WLI）to AFI and AFI to WLI. Colonic tumors are shown as distinct purple areas in the surrounding green mucosa using AFI, so AFI is expected to improve the detection rate of colonic tumors during screening colonoscopy, especially for the flat lesion which is difficult to detect using WLI.

　According to the previous report,AFI was better able to detect tumors than WLI in the right-sided colon but not in the sigmoid colon. AFI could not fully realize its ability in the narrow and tortuous sigmoid colon. Recently, we have attached a transparent hood to the tip of the AFI colonoscope and are now conducting a randomized controlled trial to evaluate the efficacy of the AFI with the transparent hood.