拡大内視鏡画像の成り立ち─胃の画像強調併用拡大内視鏡

Mechanisms Underlying the Visualization of Gastric Mucosal Anatomy and Pathology by Magnifying Endoscopy with an Image-enhanced Endoscopy Technique

要旨●画像強調観察を併用した胃拡大内視鏡所見の成り立ちを生体光学の理論を用いて概説した．粘膜においては，主に，光の反射，散乱，伝播・拡散，吸収という現象が重要である．腺窩辺縁上皮については，光を上皮に投射したときに細胞内小器官や核で起こされた後方散乱が垂直方向に集積すると白色半透明の帯状の上皮構造として視覚化される．粘膜上皮下微小血管については，光の吸収という現象から成り立っている，白色不透明物質については，微小な脂肪滴が①高い屈折率を有するため投射した光が反射されること，②微小な脂肪滴が強いMie散乱粒子であるので，細胞内で多重散乱を引き起こすこと，の2つのメカニズムにより，血管を不透明にする白色の物質として人間の目は認識している．このような，拡大内視鏡画像の物理化学的成り立ちを理解すれば，画像診断に加え今後の病態解明にも応用できる可能性が期待される．

　The mechanisms underlying the visualization of gastric mucosal anatomy and pathology by magnifying endoscopy with an image-enhanced endoscopy technique were demonstrated using bio-optic theories. It is important to understand the phenomena of reflection, scattering, propagation, diffusion, and absorption of light while analyzing endoscopic images of the gastrointestinal mucosa. Marginal crypt epithelium is visualized as a semi-transparent, whitish, band-like epithelial structure due to the vertical accumulation of backward scattering caused by organelles and nuclei within vertically arranging epithelial cells. Subepithelial microvessels are visualized as a result of the absorption of projected light. Regarding the visualization of a white opaque substance, the following two mechanisms are considered：（1）strong reflection of projected light due to the high refractive index of lipid micro-droplets and（2）intense multiple scattering originating from the multiple lipid micro-droplets with the high Mie scattering coefficient. Because human eyes recognize the reflex and scattering of light as a white color, the lipid micro-droplets were visualized as a white substance that obscures the subepithelial microvessels. As demonstrated in this article, if we understand the mechanisms underlying the visualization of magnifying endoscopic images according to bio-optics, magnifying observation can be used to investigate the pathogenesis of gastrointestinal disorders as well as to diagnose mucosal lesions.