Changes in autofluorescence emission intensities of human colonic tissues due to photobleaching process

Changes in autofluorescence intensities at 550, 580, 680 and 720 nm as functions of incident intensity and exposure time were measured in normal mucosa and adenocarcinomatous of human colonic tissues when excited by the wavelengths of 457.9, 488, 514.5 and 632.8 nm, respectively. The obtained results show that the photobleaching process of the autofluorescence follows a double-exponential function. The slower decay rates of the photobleaching at 550 and 580 nm emissions could be found in normal tissues compared to those in tumor tissues, however, the faster decay times at 680 and 720 nm emissions were also found in normal tissues. It appears that the quantitative measurements of photobleaching processes may provide a method to evaluate the fractional contribution of the autofluorescence from different layers in the colon tissues. The evaluation of temporal behavior of photobleaching processes of autofluorescence emissions may also reveal the different accumulated concentrations of endogenous fluorophores between normal and tumor tissues.