Time-resolved spectrofluorometer for clinical tissue characterization during endoscopy

Time-resolved fluorescence spectroscopy has the potential to provide more i nformation for the detection of early cancer than continuous wave spectrosc opy. A new optical fiber-based spectrofluorometer for time-resolved fluores cence spectroscopy of biological tissue during clinical endoscopy is presen ted. The apparatus is based on a nitrogen laser pumping a dye laser as exci tation source and a streak camera coupled with a spectrograph as time-resol ved spectrometer. The excitation and fluorescence light is carried by an op tical fiber to the tissue under investigation and back to the detector, res pectively. This optical fiber can be inserted into the biopsy channel of a conventional endoscope. Hence, the apparatus can be used to perform in situ tissue characterization during endoscopy. The instrument enables the measu rement of the decays of entire fluorescence spectra within 15 s with a dyna mic range of the spectro-temporal images of up to three orders of magnitude . Luminescence lifetimes from the sub ns up to the ms range can be measured . Spectral and temporal resolution, sensitivity, and dynamic range of the i nstrumentation were determined. The accuracy of the apparatus was checked b y the measurement of the fluorescence lifetimes of various fluorophores wit h known lifetimes. For the first time, two-dimensional time-resolved spectr a with sub-ns temporal resolution of tissue fluorescence of the human bladd er, the bronchi, and the esophagus taken during endoscopy are presented as a demonstration of performance of the instrumentation. The excitation wavel engths were 337 nm in the case of the bladder and the esophagus and 480 nm in the case of the bronchi. Lifetime contrasts between normal and neoplasti c tissue were found in all three organs. The spectral analysis of the fluor escence decays showed that the fluorescence between 370 and 490 nm, excited at 337 nm, consisted in several overlapping spectra. In the case of the es ophagus, the contrast between normal and tumoral tissue was inverse in two different spectral bands proving the importance of the choice of the approp riate spectral range for time-resolved autofluorescence measurements for an optimal contrast. The in vivo fluorescence decay of the photosensitizers 5 -aminolevulinic acid hexylester hydrochloride-induced protoporphyrin IX was measured in the human bladder and found to be mono-exponential with a life time of 15.9 (+/- 1.2) ns. An in vivo fluorescence lifetime of 8.5 (+/- 0.8 ) ns was found in the case of the photosensitizer 5, 10, 15, 20-tetra(m-hyd roxyphenyl)chlorin (mTHPC) in the esophagus. (C) 1999 American Institute of Physics. [S0034-6748(99)04109-X].