Therefore, light that is used for therapeutic applications must be absorbed by a specific chromophore in the biological tissue. The chromophore may be endogenous, such as a hemoglobin or protein molecule, or exogenous, such as a photosensitizing dye. Diagnostic photomedicine Diagnostic photomedicine incorporates the interaction of light with biological tissues. In this case, information may be acquired from scattered light as well as from absorbed light. Optical imaging is capable of spatial resolution and spectral resolution.
Spatial resolution is the visualization of a physical entity, such as a tumor.
Spectral resolution yields information about the identity or quantity of tissue constituents. Optical measurements are often analyzed with theoretical mathematical models of photon migration. Light energy is deposited in tissue as the photons are absorbed in the tissue. The absorbed energy is largely converted to heat. The body's vascular system removes heat from the treated area over a period of time.