A toroidal high-intensity focused ultrasound (HIFU) transducer was used to noninvasively treat liver tissues in vivo in a pig model. The transducer was divided into 32 concentric rings with equal surface areas operating at 2.5 MHz. First, attenuation of skin, fat, muscle and liver tissues was measured in fresh animal samples to adjust the energy delivered to the focal zone. Then, 8 animals were included in the present protocol and placed in a dorsal decubitus proclive position at an angle of 15°. The device was held by hand, and sonications were performed during apnea. Two thermal HIFU lesions were created in 40 s in each animal.

The average abdominal wall thickness was 14.8 ± 1.3 mm (12.5-17.6). The longest and shortest axes of the HIFU ablations were 20.9 ± 6.3 mm (14.0-33.7) and 14.2 ± 5.5 mm (7.0-22.0), respectively. All HIFU lesions were visible on sonograms. The correlation between the dimensions of the HIFU lesions observed on sonograms and during gross examination was r = 0.84. Creating large and fast ablations with reliable ultrasound imaging guidance in the liver using this handheld device may represent a new therapeutic option for patients with liver tumors.