Measurement and Thermal Dependence of Biological Tissue Optical Properties

The light-tissue interaction process inherent to almost every biomedical application of light is determined by tissue optical properties. Generally, the most important optical properties are absorption coefficient, scattering coefficient and reduced scattering coefficient, scattering anisotropy factor, and refractive index. This chapter provides an overview of methods that have been developed for measurement of these properties and discusses the thermal factors that can alter them. Recent investigations of tissue photocoagulation using nanoparticles have tended to overlook a key processes that was well known and studied 10-30 years ago: thermally induced dynamic changes in optical properties. The increase in scattering due to thermal denaturation of proteins is a well-known process that is ubiquitous in high-power laser therapy techniques. As optical-thermal models become more sophisticated and temperature/damage-dependent optical property data become available, these dynamic effects will be predicted with greater accuracy.