Imaging and Photodynamic Therapy: Mechanisms, Monitoring, and Optimization

The current state of the role of imaging in photodynamic therapy (PDT) has been reported. PDT is a photochemistry-based approach that uses a light activatable chemical, termed a photosensitizer (PS), and light of an appropriate wavelength to impart cytotoxicity via the generation of reactive molecular species. The ability to accurately define tumor margins is a crucial aspect in optimization of surgical interventions and constitutes a major subset of the applications of this fluorescence imaging technique. The traditional implementation of PDT involves the administration of a synthetic PS followed by a period of delay, in which the PS accumulates in the tumor or tissue of interest, before light activation. A major drawback of conventional imaging strategies using one-photon excitation is the limited penetration of visible light into tissue. Progress in imaging technologies, targeting chemistries, and nanotechnology combined with a detailed understanding of PDT-related molecular mechanisms provides optimism for the future of imaging in PDT and may be an important conduit for new applications of PDT and for the development of patient individualized treatments.