Mechanistic and diagnostic aspects of photodynamic enhancement and stone fragmentation

Metastable oxygen molecules in the singlet delta state, O2(1Δ), are believed to be the active species that are produced during laser irradiation of hematoporphyrin derivative (HPD), attached to tumors, and are responsible for cancer cell destruction. Although the presence of O2(1Δ) has been inferred by indirect chemical measurements, it has not been detected in real time. In this work, we review the optical characteristics of O2(1Δ) and describe an optical diagnostic procedure for its real-time detection during laser irradiation. In vitro experiments using both pulsed and cw dye lasers are described. Additionally, recent work has been presented whereby repetitively pulsed dye laser radiation can be delivered through a fiber-optic probe to induce fragmentation of kidney stones and gallstones.