Multi-colour fluorescence imaging in connection with photodynamic therapy of δ-amino levulinic acid (ALA) sensitised skin malignancies

A system for multi-colour fluorescence imaging of tissue is described. The instrument is mainly developed for tissue diagnostics to identify and localise malignant tumours, but might also be useful for real-time monitoring of the therapeutic dose delivered during photodynamic therapy. In vivo examples from various malignant skin lesions following topical δ-amino levulinic acid (ALA) administration are presented. The diagnostic system utilises both characteristics of a fluorescent tumour marker, such as a porphyrin containing substance, and the native tissue autofluorescence to characterise the tissue. A dimensionless function of three or four simultaneously recorded fluorescence intensities is formed and an optimum-contrast image is calculated pixel-by-pixel.