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Summary form only given. A sufficiently narrow directivity pattern of IR radiometers can be obtained with the help of an optical system (made of lenses or a parabolic/hyperbolic mirror) located at the input. However, in a number of applications it seems reasonable to use diaphragm optics. The advantages of diaphragm optics are attributed to its dust immunity, mechanical stability and simplicity of manufacturing. The fact that it can be placed after a modulator is also considered as a benefit-in this case thermal radiation of the optical system is not modulated and the error arising from reradiation of the optical system is fully eliminated.

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 /spl Delta/l 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 T/sub 2/-T/sub 1/, depth of occurrence /spl Delta/l/sub 1/, inhomogeneity dimension /spl Delta/l/sub 2/ and tissue type. The dependence of increment /spl Delta/T-eff on the absorption coefficient (/spl alpha/) of a uniform tissue with a temperature inhomogeneity has a marked extremum. /spl Delta/T-eff maximum is shifted in the range of small parameters (/spl alpha/) with the increase of layer depth /spl Delta/l/sub 1/ and /spl Delta/l/sub 2/ (that corresponds to longer wavelengths). At a constant value of intermediate tissue /spl Delta/l the dependence of /spl Delta/T eff on the /spl alpha/ "hot" area dimension decreases with the increase of (/spl alpha/) (the wavelength decrease) and at some value of (/spl alpha/) 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(/spl alpha/) except for the value of T-eff (step-function approximation, for example, T-eff decreases at all values of (/spl alpha/) 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 /spl Delta/T-eff. The maximum occurs at the wavelength where there is a minimum contribution from the "hot" area. At large values of (/spl alpha/) (long wavelengths) and small dimensions of the thermal inhomogeneity the increment of /spl Delta/T-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.