Thermal Diffusion in High Intensity Focused Ultrasound

Abstract

Abstract: The Pennes’ bio-heat transfer equation is solved for a point heat source in pulse or CW modes, respectively. These solutions are further applied to the actual set (HIFU) to predict its temperature elevation and cooling processes and several concise analytical expressions are obtained. The results demonstrate that the temperature elevation is proportional reciprocally to the blood perfusion rate and the temperature during the cooling process is reduced exponentially with the increase in blood perfusion rates. It also shows that the higher temperature elevation will be generated when the set works in CW mode than in pulse mode. The appearance and shape of the focal spot in the tissues heated by HIFU set is similar to the isoline of the acoustic intensity as long as the heating dosage is sufficient. Moreover, an acoustic method to measure the blood perfusion rates in vivo is suggested.