LASER-INDUCED AUTOFLUORESCENCE DIAGNOSIS OF TUMORS

The feasibility of routine real-time clinical detection of precancerou s lesions such as severe dysplasia and carcinoma in situ (CIS) by lase r induced autofluorescence (LIAF), that is without the use of exogenou s fluorescent marker, has been recently demonstrated in several medica l fields. We present here an in vivo autofluorescence study we have un dergone on normal, suspicious and tumoral areas of human bladder. Thre e different pulsed laser wavelengths were alternately used for excitat ion: 488 nm (Dye laser), 337 nm (Nitrogen laser), and 308 nm (XeCl exc imer laser). A clinical endoscopic study was performed on 25 patients. Spectroscopic results were compared with histological analysis. For 4 88 nm and 337 nm excitation a single fluorescence broad band was obtai ned in any case, but for tumors the overall intensity was significantl y reduced compared to normal mucosa. For 308 nm excitation we observed two main broad bands, centered respectively at about 360 nm and 440 M n. In case of neoplastic lesions (including carcinoma in situ), the in tensity ratio [I(360nm)/I(440nm)] was always greater than 2, for norma l or inflammatory areas it was less than 2. A clear diagnosis could th en be achieved for 308 nm excitation with no need of absolute intensit y measurements. However, in turbid media, the optical properties of th e medium are wavelength dependent. As a consequence the observed fluor escence signals are different from the isolated fluorophores spectra a nd their shape depends also on the illumination and detection geometry . We show how this phenomenon can be taken into account for useful com parison of results from different groups.