In vivo EXCITATION OF PHOTOSENSITIZERS BY INFRARED LIGHT

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Abstract
Use of near infrared instead of visible light would markedly improve tissue penetration, making larger tumors candidates for photochemotherapy. Because common photesensitizers exhibit virtually no absorption in this wavelength region, conditions are required where the simultaneous action of two photons is possible. Healthy tissue (rat ears), sensitized by hematoporphyrin derivative, sulfonated chloroaluminum phthalocyanine or pheophorbide alpha, was irradiated (1064 nm, 10 ns) with power densities up to 200 MW cm-2 and total energy densities up to 200 kJ cm-2. No reproducible photodynamic lesions were observed, but there was sensitizer fluorescence that depended quadratically on the excitation intensity.