Photodynamic assay of light distributions in tissue phantoms

The distribution of light in tissues of varying blood content has been modeled using a gel agar system as a tissue phantom. Hematoporphyrin derivative (Photofrin I or HpD) was suspended in gels, along with a chemical indicator of its cytotoxic intermediate (singlet oxygen), and various amounts of red blood cells. The singlet oxygen detector used was tryptophan and its oxidation product. Qualitative analysis of the tryptophan photoproduct was determined using high-pressure liquid chromatography analysis of individual gel sections. The relative amount of photoproduct was used as a measure of the fluence of actinic light at a given depth within the tissue phantoms. In this manner, the relative activation efficiencies of HpD were determined for light from an argon laser (mainly 488 and 514.5 nm) and an argon-pumped dye laser (630 nm).