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

Topical or systemic administration of 5-aminolaevulinic acid results in biosynthesis of the photosensitiser protoporphyrin IX (PpIX) with some selectivity for malignant lesions. Excitation near 400 nm excites both intrinsic green tissue autofluorescence and red fluorescence from PpIX which may be exploited 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 ratio imaging. The red to green fluorescence intensity ratios were calculated for each pixel in real-time and fluorescence ratio images were displayed typically at a rate of 2 frames/s. Laboratory tests of fluorescence ratio imaging showed good contrast enhancement between control tissues and tissue phantoms and those containing porphyrin photosensitisers. In preliminary clinical tests, a clear demarcation between neoplastic/ cancerous lesions and adjacent normal tissue was demonstrated. The extent of PpIX photobleaching during photodynamic therapy was also investigated using fluorescence ratio imaging.