IN-VIVO LASER-INDUCED FLUORESCENCE IMAGING OF A RAT PANCREATIC-CANCERWITH PHEOPHORBIDE-A

Laser-induced fluorescence (LIF) of pheophorbide-a (Pha) was used for imaging of a rat pancreatic tumor. Using a dimensionless function (the ratio of Ph-a fluorescence by bluish autofluorescence), the fluoresce nce contrasts between excised tumors and their paired pancreas were in vestigated up to 48 h after a 9 mg kg(-1) Ph-a intravenous administrat ion. Among five tested excitation wavelengths, 355 and 610 nm excitati ons gave the best distinctive contrasts, both 48 h after dye injection . The LIF imaging of six intrapancreatic tumors and six healthy pancre as was carried out in vivo using two laser excitations: 355 nm (Nd:YAG + tripling) for bluish autofluorescence and 610 nm (rhodamine 6G dye) for reddish autofluorescence and dye emission. Images were recorded t hrough bandpass filters at 470 and 640 nm (autofluorescence) and at 68 0 nm (dye + autofluorescence) with an intensified charged-coupled devi ce camera. Autofluorescence as Ph-a fluorescence images did not allow accurate LIF diagnosis of pancreatic carcinoma. An image processing, i ncluding for each pixel a computed division of Ph-a fluorescence (afte r subtraction of reddish autofluorescence) by bluish autofluorescence intensity generated poorly contrasted tumor images in five of six and false tumor localization in one of three of the tumor-bearing pancreas . A fitting of the digital 640 nm autofluorescence up to the mean 680 nm fluorescence intensity in pancreas prior to subtraction allowed a s afe diagnosis to be made with well-contrasted tumor images. To assess automation ability of the processing, a same fitting coefficient (mean of individual values) was applied, In this way, false-negative (one o f six) and false-positive (two of six) images were present in tumor-be aring animals as false-positive in one-half of the controls. A success ful standardized procedure was then applied with a normalization of 64 0 and 680 nm pancreas intensities to a same set threshold prior proces sing. In opposition to thin-layered hollow organs, such as bronchial t ube or digestive tract, LIF imaging of carcinoma inserted in a compact organ is exhausting. The use of a dye excitable in the red wavelength range (610 nm for Ph-a) may partly solve this problem, rendering LIF imaging more accurate and potentially automated.