Application of protoporphyrin IX (PpIX)-to-photoprotoporphyrin (PPp) fluorescence ratio to imaging of metastatic gastric cancer in excised lymph nodes

Abstract

Fluorescence of protoporphyrin IX (PpIX) is useful for diagnosis of metastatic cancer in lymph nodes. PpIX is selectively accumulated in cancer tissues. However, autofluorescence arising from background tissues is an obstacle for specific detection of PpIX fluorescence. When PpIX is converted to photoprotoporphyrin (PPp) after exposure to light, the fluorescence peak is shifted from 635 nm to 675 nm. Since the shift of the fluorescence peaks is unique in PpIX, the acquisition of the shift is helpful in specific detection of PpIX in tissues possessing autofluorescence. In this study, we sought to develop a method to specifically detect PpIX fluorescence in autofluorescent tissues. The results showed that the method aided in detecting PpIX fluorescence in metastatic gastric carcinoma in resected lymph nodes.