Monte Carlo simulation of the fluorescence spectra of colon and cervical tissues at different dysplasia grades

Monte Carlo modeling was developed for simulating the light induced autofluorescence spectra of colon and cervical tissues at different dysplasia grades.These tissues were frozen sliced into 100 um thickness. The transmittance (Ta) and backscatter spectra (Ra) of these tissues were measured using double integral sphere system. The scattering coefficient, μs, and absorption coefficient, μa, were determined by the inverse adding-doubling (IAD) method from the Ta and Ra. spectra. The fluorescence intensity and spectra of these sliced tissues were measured using spectrometer system with cooled 2D CCD array. We simulated light energy distribution in tissue at 330 nm excitation and then convolution with fluorophores intensity and escape function in each tissue layer. The results of the simulation show: (1)fluorescence spectra change with different tissue characteristics, (2)fluorescence intensity decrease with the development of the dyplasia grades and the mucosa thickness, (3)the relative collagen signal decreases, hemoglobin signal increases, and NADH signal increases along with the dyplasia development. The simulated results matched well in vivo measured results. The approach provides an important means for understanding tissue fluorescence spectra's changes that are very critical for clinic diagnosis.