Comparison of thermal ablation criteria for nonlinear regimes of ultrasound irradiation of biological tissue using a multi-element phased array

In this paper different criteria of thermal ablation induced by high intensity focused ultrasound in clinically significant volumes of biological tissue were compared. Sonications using a multi-element ultrasound array and various nonlinear focusing regimes were considered in numerical experiment. Sonication of tissue was maintained until thermal dose reached a threshold value at the circle of a certain radius. The threshold temperature was chosen so that the sonication stopped at the same time when using the criteria of temperature or dose. Threshold temperatures equivalent to the thermal dose threshold achieved at the end of the heating were obtained. Volumes of thermal lesions in tissue were calculated using both the criteria of thermal dose and temperature. It was shown that the use of the threshold temperature criterion corresponded with good accuracy to the thermal dose criterion in case of the uniform heating of the tissue volume.