In the experiment, the features of laser interstitial thermotherapy (LITT) with wavelengths of 0.92; 0.97; 1.06; 1.56 and 1.9 μm and the possibility of estimating photothermal interactions by means of ultrasoundwere studied. Ultrasound clearly determined the tissue coagulation zone without differentiating it from carbonation. The phenomenon of "breakdown" of tissues during LITT was revealed. Most often at 1.9 Μm-LITT there was a rapid transfer of heat by gas bubbles through the vessels. Intima of the vessels was fired. Ultrasound control of LITT in 145 of 781 children with vascular tumors increased its effectiveness, reducing the number of repeated sessions by 3.2 times.
Two families of new non-analog algorithms of the Monte Carlo method are suggested for calculation of linear characteristics of optical radiation field in turbid heterogeneous media, biological tissues, first of all. One of the families is specifically aimed at calculating the readings of small-aperture radiation detectors. The algorithms allow us with high differential accuracy simultaneously for a large set of the media with different optical parameters (including phase function ones) to calculate the readings of detectors and their derivatives with respect to the parameters. This makes the algorithms high perspective for solving inverse problems of biomedical optics, in particular, for determination of optical parameters of biological tissues from measurements of radiation characteristics. The result is obtained using a rigorous approach based on the theory of Monte Carlo method for linear integral equations. For this purpose, we wrote (in the framework of the kinetic model) the adjoint integral representations for linear radiation characteristics in a heterogeneous turbid medium, correctly considering the reflection and refraction of the light on the surfaces of refractive index discontinuity.
A new method for non-invasive determination of optical parameters (absorption and reduced scattering coefficients) of biological tissues from diffuse reflectance measurements with a multifiber probe is presented. For extraction of the parameters, we use a priori estimations not only of signals of detectors, but also their parameter derivatives that increases accuracy of the extraction. This estimation is performed using a new non-analog Monte Carlo algorithm which allows us to calculate the signals and derivatives simultaneously for a given large set of optical parameters. Experimental testing has shown the measured coefficients provide a good prediction of both light reflection and penetration. Application of the method to some biological tissues are presented.
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