Photodynamic diagnosis with 5-aminolevulinic acid for intramucosal cancer using green light

Photodynamic diagnosis (PDD) of gastric cancer with protoporphyrin IX (PpIX) induced by 5 -aminolevulinic acid (ALA) will lead to a method to estimate the invasive depth. The excitation light for ALA-based PDD is attenuated by absorption and scattering of the mucosal tissue according to its wavelength and the difference contains the fluorophore depth information. To realize the method to estimate the invasive depth for the intramucosal cancer, this study investigated the differences of the attenuation rate between two excitation wavelengths. Considering the optical properties of mucosa and PpIX, relationships between the invasive depths of cancer containing PpIX and the fluorescence intensity ratios detected from the mucosa were estimated using a numerical model. An experiment was also performed using a pellet made of epoxy resin containing PpIX. The excitation lights with wavelengths of 405 and 505 nm having the same power density were each used to irradiate the pellet placed at the fluorophore depth of 0 mm, 1.0 mm, and 1.7 mm from the mucosal surface to obtain fluorescence images, and the average fluorescence intensities of the images were evaluated. The numerical and experimental results suggested the possibility to estimate the fluorophore depth of the PpIX fluorescence source by comparing the fluorescence images with excitation lights at wavelengths of 405 and 505 nm.