Some results of looking for thermal inhomogeneities in biological tissues by radiometric methods

Summary form only given, as follows. Radiometric methods of thermal inhomogeneities localization are very promising in medical diagnosis and treatment control (particularly, hyperthermia control). We have considered some cases of temperature inhomogeneities in the form of a finite depth layer Δl with different temperature distribution from the surface (l=0) to depth. It has been shown on the basis of the radiation transport theory that the increment of the radiation effective temperature due to a temperature inhomogeneity depends on the temperature gradient T₂-T₁, depth of occurrence Δl₁, inhomogeneity dimension Δl₂ and tissue type. The dependence of increment ΔT-eff on the absorption coefficient (α) of a uniform tissue with a temperature inhomogeneity has a marked extremum. ΔT-eff maximum is shifted in the range of small parameters (α) with the increase of layer depth Δl₁ and Δl₂ (that corresponds to longer wavelengths). At a constant value of intermediate tissue Δl the dependence of ΔT eff on the α "hot" area dimension decreases with the increase of (α) (the wavelength decrease) and at some value of (α) it does not depend on the "hot" area depth. It has been noted that the approximation function of physical temperature T into tissue depth does not generally affect the type of T eff=f(α) except for the value of T-eff (step-function approximation, for example, T-eff decreases at all values of (α) as compared with the piecewise linear approximation). All these results have an obvious physical interpretation. The radiometer registers the radiation of intermediate tissues and a part of "hot" area radiation. At small wavelengths the main contribution in the brightness temperature is given by tissue subsurface layers. With the increase of the wavelength the radiometer grips other parts of the "hot" area and there is a growth of ΔT-eff. The maximum occurs at the wavelength where there is a minimum contribution from the "hot" area. At large values of (α) (long wavelengths) and small dimensions of the thermal inhomogeneity the increment of ΔT-eff tends to a constant value since the contribution from the second "cold" area will be dominant. Thus there is an optimal wavelength band from the viewpoint of the effective temperature increment maximum. This wavelength band is determined by the tissue type, inhomogeneity dimension and location