[Effects of therapeutic dose on temperature rise induced by high intensity focused ultrasound in tissue]

Based on the well-known Pennes' bioheat equation, we analyzed theoretically the temperature rise in tissue during high intensity focused ultrasound(HIFU) irradiation, and measured the focal temperature rise induced by HIFU in the treatment of freshly excised cow liver with different acoustic intensity and exposure time. The results showed that a threshold exposure time always existed under a certain acoustic intensity. Temperature rise was slow when exposure time exceeded the threshold exposure time. The greater the acoustic intensity was, the earlier the threshold time appeared. The focal temperature rise and the relative cumulative thermal dose (RCTD) increased with the increase of acoustic intensity and exposure time. For a certain therapeutic dose, the effects of acoustic intensity on focal temperature rise were more distinct than the effects of exposure time on focal temperature rise. Therefore, the optimal HIFU therapeutic dose should meet the need, i.e. moderate acoustic intensity, and the exposure time be the threshold exposure time under this acoustic intensity.