Comparison of pathway in high intensity focused ultrasound (HIFU) lesion production

High intensity focused ultrasound (HIFU) is being evaluated for non-invasive treatment of solid tumors. The temperature at the HIFU focus can reach over 65 deg C denaturing cellular proteins and resulting in coagulative necrosis and lesion formation. One common method for delivering HIFU therapy clinically is using the spot accumulation method that delivers sequential individual treatment spots. Because of thermal diffusion from nearby treatment spots, the size of subsequent lesions will gradually become larger as the HIFU therapy progresses, which may cause insufficient treatment of the initial spots, and over-treatment of later spots unless parameters are changed during treatment. A new pathway for HIFU treatment is proposed and compared with the conventional sequential path. Modeling, in vitro phantom and ex vivo bovine liver experiments demonstrate that the new treatment path produces more uniform lesions than the conventional treatment path (p<0.05). The relationship between lesion area/volume and delivered ultrasound energy and dose-dependent discrepancies between scanning paths were also studied. In addition, the temperature changes in the ex vivo system were measured using a thermocouple array. Altogether, the new treatment path appears to be advantageous for producing more uniform lesions without modifying HIFU parameters during treatment or significantly increasing the scanning time.