Quantitative detection of protoporphyrin IX (PpIX) fluorescence in tissues

In situ quantification of photosensitizer is critical in photodynamic therapy (PDT) and photodiagnosis (PD). Fluorescence detection is a feasible approach for the quantification of fluorescent photosensitizer. However, due to the interference of tissue absorption and scattering on the fluorescence spectrum of photosensitizer, it is still challenging to perform in situ fluorescence quantification. In this preliminary study, a Monte Carlo (MC)-based method was used to simulate the fluorescence spectrum and diffuse reflection spectrum of different biological tissues. A calibration algorithm was developed for the correction of the influence of tissue absorption and scattering on protoporphyrin IX (PpIX) fluorescence. Under the excitation of blue light of 405 nm the dispersion coefficient of the original PpIX fluorescence spectrum of the soft tissue phantoms was 28%, which was reduced to 3% after the correction using the calibration algorithm. Under the excitation of red light of 635 nm, the dispersion coefficient of the original PpIX fluorescence spectrum of the soft tissue phantoms was 25%, which was reduced to 1.5% after the correction using the calibration algorithm. The results show that the MC-based method can effectively improve the accuracy of PpIX fluorescence measurement.