In vivo fluorescence spectroscopy to optimize the detection of early bronchial carcinoma by autofluorescence imaging

Autofluorescence bronchoscopy is a promising approach to detect and characterize precancerous and early cancerous lesions. Nevertheless, many spectral features of photodetection systems remain unclear and sub-optimal at the present time. We report here a comprehensive study of the autofluorescence of the human healthy, metaplastic, dysplastic and cancerous bronchial tissues, covering a range of excitation wavelengths going from 350 nm to 480 nm. Moreover, the absolute values of these tissue autofluorescence yields were determined. These measurements were performed with a spectrally and intensity calibrated optical fiber-based spectrofluorometer which has been designed to optimize the spectroscopy conditions encountered by an endoscopic fluorescence imaging system. Our data yield information about the excitation and emission windows to be used in a bispectral detection imaging system. We found that the order of magnitude of the autofluorescence brightness is stable as the excitation varies from 350 to 495 nm (on the order of 5 nW/mW × nm). We also found that the use of backscattered red light instead of red autofluorescence enhances the "lesion/normal" tissues contrast. The excitation wavelengths yielding the highest contrasts are between 400 and 480 nm with a peak at 405 nm. It was finally observed that the transition wavelength for bispectral fluorescence imaging systems is around 590 nm, regardless of the excitation wavelength.