Stomach and intestine neoplasia fluorescence detection using 5-ALA/PpIX photosensitization

Abstract

In the recent study delta-ALA/PpIX is used as fluorescent marker for tumor detection in stomach, small intestine and colon. 5-ALA was administered per os two hours before measurements at dose 20 mg/kg weight. Twenty laboratorial rats with developed neoplasia in gastrointestinal tract were used. Three of them formed control group - without application of exogenous 5-ALA/PpIX, as a contrast fluorescent marker. Their spectral properties were evaluated and used for correction of endogenous sources of fluorescence from stomach and intestine lesions detected. Macroscopic fluorescence spectroscopy parameters of gastrointestinal tissues of the other 17 animals, which were sensitized with 5- ALA?PpIX, were obtained on excitation at 405 nm. Excitation and emission light was delivered by fiberoptic probe 6+1 to the organs investigated in vivo during open surgery procedure on the laboratorial animals used. The fluorescence detected from tumor sites has very complex spectral origins. It consists of autofluorescence, fluorescence from exogenous fluorophores and re-absorption from the chromophores accumulated in the tissue investigated. Spectral features observed during endoscopic investigations could be distinct as the next regions: 450-630 nm region, where tissue autofluorescence is observed; 630-710 nm region, where fluorescence of PpIX is clearly pronounced; 530-580 nm region, where minima in the autofluorescence signal are observed, related to re-absorption of oxy-hemoglobin in this spectral area. The contrast achieved in normal vs. neoplastic gastrointestinal tissues was evaluated. Influence of endogenous 5-ALA/PpIX accumulation was taken into account; as well the role of inflammatory processes on the PpIX distribution and accumulation into the body was evaluated. Dimensionless ratio R=I635/I560 is evaluated as highly informative one for development of a simple algorithm for differentiation, which could has high diagnostic accuracy for evaluation of tumor vs. inflammatory vs. normal mucosa, using 1-D spectral results. Very good correlation between fluorescence data and histology examination of the lesions investigated was achieved as well.