ABSTRACT

The application of lasers and other optical technology to problems in biomedicine is a rapidly growing field. These applications can be classified as diagnostic or therapeutic. In a diagnostic application, the goal is to learn something about the physiology or pathology of the tissue through its interaction with light. For example, the fluorescence emitted by tissue after laser excitation is characteristic of its chemical composition which, in turn, can depend on the nature and stage of certain diseases such as cancer [1]. The fundamental optical processes that can be exploited for diagnostic information are absorption, scattering (both elastic and inelastic) and luminescence (both fluorescence and phosphorescence). Most often optical diagnostics rely on interaction with endogenous tissue constituents but it is also possible to administer an exogenous agent that interacts with light. For instance, a bolus injection of indocyanine green, an infrared absorbing dye, has been used to measure blood flow in specific organs [2]. The interpretation of a diagnostic optical measurement may be based on empirical correlation with other data or it may require a thorough understanding of the particular light-tissue interaction being used as well as the propagation of light within the tissue.