Focal region of high intensity focused ultrasound combined with ultrasound contrast agent on rabbit liver

Objective To evaluate the efficacy of high intensity focused ultrasound (HIFU) combined with ultrasound contrast agent on rabbit liver, and to investigate the possibility of ultrasound contrast agents enhancing the effect of HIFU on rabbit liver. Methods Thirty-two rabbits were averagely divided into two groups according to their body mass. Rabbits in group Ⅰ were irradiated by HIFU alone on the liver, and those in group Ⅱ were treated by irradiation of HIFU after intravenous injection of a ultrasound contrast agent. The used treatment time, frequency, power and the distance from focus to the skin surface were identical in the two groups. The changes of ultrasound image were recorded at the 20 s, 2 min and 5 min after treatment. Four rabbits in each group were slaughtered for morphological and pathological examination immediately and on the 2nd, 3rd and 7th day after the treatments, respectively. Results The ultrasonic gray scale differenced in the HIFU alone group were ( 20.12± 12.4)s (20 s), ( 16.8± 9.3)min (2 min) and ( 15.1± 11.9)min (5 min). Compared with those in the enhanced HIFU group were ( 63.9± 29.4)s, ( 60.0± 25.9)min, ( 59.3± 28.7)min, respectively(P 0.05). The focal region of HIFU group[( 130.5± 200.2)mm 3] differed significantly from that of enhanced group[( 1613.6± 2620.7)mm 3](P 0.05). The tissue structure of target areas was ruptured immediately after HIFU treatment. Pyknotic nuclei were seen in most of the hepatic cells. Clear demarcation between coagulation necrosis and the normal tissue was seen on the 2nd, 3rd and 7th day. Conclusions Ultrasound contrast agent could change the acoustic environment of the rabbit, and enhance the efficacy of HIFU on rabbit liver. Ultrasound contrast agents would be useful as a HIFU enhancing agent on clinical treatment of solid tumor.