THERMAL PROPERTIES OF BIOLOGICAL TISSUE GEL-PHANTOMS IN A WIDE LOW-TEMPERATURE RANGE

It is often impossible or impractical to conduct experiments on cooling, freezing, and thawing during medical cryoexposures with using biological tissues. In such cases, gel-phantoms are used. Due to the lack of accurate data, the defi nition of the thermal properties of gel-phantoms is relevant. The current study presents the results of the thermal properties measurements with using the differential scanning calorimetry (DSC) and transient hot bridge (THB) methods and of their analysis for fi ve gel-phantoms: 1) 95% water and 5% gelatin; 2) 95% water and 5% agar-agar; 3) 94% water, 3% gelatin, 2.5% agar-agar, and 0.5% sodium chloride; 4 and 5) ultrasound gels. The values of the effective specifi c heat capacity from –160 to 40^o C, thermal conductivity, moisture content, freezable water fraction, and of the initial melting and cryoscopic temperatures are determined. The obtained results are compared with the values of the thermal properties of biotissue and distilled water. The infl uence of the gelphantom type on the character of phase transition is shown. Adaptation of the experimental data for cryoexposure simulation software is proposed. Recommendations for selecting a phantom are given. The impact of simplifi cation of the thermal properties on the thermal diffusivity is estimated. The data for calculating the properties of phantoms of different composition are proposed.
It is often impossible or impractical to conduct experiments on cooling, freezing, and thawing during medical cryoexposures with using biological tissues. In such cases, gel-phantoms are used. Due to the lack of accurate data, the defi nition of the thermal properties of gel-phantoms is relevant. The current study presents the results of the thermal properties measurements with using the differential scanning calorimetry (DSC) and transient hot bridge (THB) methods and of their analysis for fi ve gel-phantoms: 1) 95% water and 5% gelatin; 2) 95% water and 5% agar-agar; 3) 94% water, 3% gelatin, 2.5% agar-agar, and 0.5% sodium chloride; 4 and 5) ultrasound gels. The values of the effective specifi c heat capacity from –160 to 40^o C, thermal conductivity, moisture content, freezable water fraction, and of the initial melting and cryoscopic temperatures are determined. The obtained results are compared with the values of the thermal properties of biotissue and distilled water. The infl uence of the gelphantom type on the character of phase transition is shown. Adaptation of the experimental data for cryoexposure simulation software is proposed. Recommendations for selecting a phantom are given. The impact of simplifi cation of the thermal properties on the thermal diffusivity is estimated. The data for calculating the properties of phantoms of different composition are proposed.
Author:  I. V. Agafonkina, A. G. Belozerov, Yu. M. Berezovsky, I. A. Korolev, A. V. Pushkarev, D. I. Tsiganov, A. V. Shakurov, A. A. Zherdev
Keywords:  thermal properties, gel-phantom, ultrasound gel, agar, gelatin, biological tissue, DSC, THB
Page:  790-802