Laser-induced autofluorescence diagnosis of tumors

The feasibility of routine real-time clinical detection of precancerous lesions such as severe dysplasia and carcinoma in situ (CIS) by laser induced autofluorescence (LIAF), that is without the use of exogenous fluorescent marker, has been recently demonstrated in several medical fields. We present here an in vivo autofluorescence study we have undergone on normal, suspicious and tumoral areas of human bladder. Three different pulsed laser wavelengths were alternately used for excitation: 488 nm (Dye laser), 337 nm (Nitrogen laser), and 308 nm (XeCl excimer laser). A clinical endoscopic study was performed on 25 patients. Spectroscopic results were compared with histological analysis. For 488 nm and 337 nm excitation a single fluorescence broad band was obtained in any case, but for tumors the overall intensity was significantly reduced compared to normal mucosa. For 308 nm excitation we observed two main broad bands, centered respectively at about 360 nm and 440 Mn. In case of neoplastic lesions (including carcinoma in situ), the intensity ratio [I(360nm)/I(440nm)] was always greater than 2, for normal or inflammatory areas it was less than 2. A clear diagnosis could then be achieved for 308 nm excitation with no need of absolute intensity measurements. However, in turbid media, the optical properties of the medium are wavelength dependent. As a consequence the observed fluorescence signals are different from the isolated fluorophores spectra and their shape depends also on the illumination and detection geometry. We show how this phenomenon can be taken into account for useful comparison of results from different groups.