Fluorescence photodiagnostics and photobleaching studies of cancerous lesions using ratio imaging and spectroscopic techniques

Topical or systemic administration of 5-aminolaevulinic acid results in bio synthesis of the photosensitiser protoporphyrin IX (PpIX) with some selecti vity for malignant lesions. Excitation near 400 nm excites both intrinsic g reen tissue autofluorescence and red fluorescence from PpIX which may be ex ploited for the optical diagnosis of malignant and premalignant disease. In this work the utility of a cooled 12-bit single chip charge-coupled device (CCD) colour camera was investigated for photodiagnostic fluorescence rati o imaging. The red to green fluorescence intensity ratios were calculated f or each pixel in real-time and fluorescence ratio images were displayed typ ically at a rate of 2 frames/s. Laboratory tests of fluorescence ratio imag ing showed good contrast enhancement between control tissues and tissue pha ntoms and those containing porphyrin photosensitisers. In preliminary clini cal tests, a clear demarcation between neoplastic/ cancerous lesions and ad jacent normal tissue was demonstrated. The extent of PpIX photobleaching du ring photodynamic therapy was also investigated using fluorescence ratio im aging.