Fluorescence diagnostics and kinetic studies in the head and neck region utilizing low-dose delta-aminolevulinic acid...

Diagnostic measurements and pharmacokinetic studies were performed in 17 patients with various kinds of malignant, premalignant and benign lesions in the head and neck region by means of point monitoring laser-induced fluorescence. For marking different types of tissue, delta-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) was used. The ALA-induced PpIX synthesis was monitored at different time intervals after oral administration of ALA in low doses, 5 and 15 mg/kg b.w. Besides the porphyrin-related signal the tissue endogenous fluorescence was also recorded. The fluorescence spectra were evaluated at two different wavelengths corresponding to the specific drug-related fluorescence peak and the endogenous tissue fluorescence emission at 635 and 490 nm, respectively. The evaluated fluorescence data were correlated to the histopathological tissue investigation. A fall-off in the overall fluorescence intensity at 490 nm was obtained for all the malignant and premalignant areas, as well as an increased red fluorescence. A ratio between the red and the blue/green fluorescence intensity was formed for each time interval after the ALA administration. The lower drug dose seems to be sufficient to obtain a useful demarcation ratio between normal and diseased tissue with a very low PpIX fluorescence intensity in the normal tissue. A PpIX fluorescence maximum seems to occur between 3 and 4 h in normal tissues, whereas malignant tumour tissue shows a higher level for a longer period of time.