Depth estimation of protoporphyrin IX objects in turbid media considering the fluorescence intensity ratio between two wavelengths of light for application in invasion diagnosis of gastric cancer

This paper demonstrates a method to estimate the depth of a fluorescence object in turbid media using dual-wavelength excited photodynamic diagnosis, to aid in the invasion depth diagnosis of gastric cancer. The treatment method for gastric cancer is determined by its invasion depth, which is difficult to measure in situ during endoscopic diagnosis. Therefore, a method that can quantitatively diagnose tumor depth using a simple optical system that can be utilized with an endoscope is required. In the proposed method, the depth of a fluorescence object in a turbid medium is estimated by considering the optical propagation of two wavelengths of excitation light and absorption properties of protoporphyrin IX. In our experiments, we evaluated the estimation accuracy of the fluorescence object depth in a tissue-mimicking phantom from a fluorescence intensity ratio during fluorescence observation based on the calibration curve obtained from prior numerical calculation. The results of the fluorescence observation experiment showed that the depth of the fluorescence object could be estimated with an error of less than 0.3 mm within 2 mm from the surface.