Einführung in die gewebeoptik und optische dosimetrie

The spatial distribution of radiation during medical laser application is determined by the characteristics of the beam (power, time, beam geometry) and the optical properties of the tissue. The irradiance E (in W/m²) describes the primary laser beam. Scattered radiation, in turn, is taken into account by the fluence rate φ (also in W/m²). The basic parameters of tissue optics are the absorption coefficient μ_a, the scattering coefficient μ_s and the anisotropy factor g. In addition, derived parameters are also used, i. e., total attenuation coefficient μ_t, reduced scattering coefficient μ_s′, effective attenuation coefficient μ_eff, mean free path of a photon d and penetration depth δ. Further tissue properties are the diffuse reflectance R_d and the back-scattering factor k. In an one-dimensional model the fluence rate φ in tissue is a nearly exponential function characterized by the penetration depth δ. At the tissue surface, the relationship exists φ=kE. This model is compared with the results of a computer program based on the finite element method.