Development of a High-intensity Focused Ultrasound Exposure Device for Reducing Skin Burn Risk

High-intensity focused ultrasound（HIFU）can non-invasively irradiate inside the body. However, when used to treat fetuses, it can cause thermal burns of the mother’s abdominal wall at the skin interface. This study was carried out to determine whether a modified HIFU transducer enabling split-aperture irradiation can prevent thermal burns. Two HIFU transducers were compared: a conventional transducer using full-aperture irradiation and a modified transducer using split-aperture irradiation. The modified transducer was divided into six sectors for split-aperture irradiation and had a larger surface area and a smaller F number（focal length/aperture diameter）than the conventional transducer. HIFU was delivered to eight sites on the left and right leg of a three-month-old baby pig under general anesthesia, and the sites were assessed for thermal burning by two or more dermatologists. The same person performed all irradiations. Full-aperture irradiation with the conventional transducer caused deep dermal burns at all target sites, while split-aperture irradiation with the modified transducer caused only epidermal burns or superficial dermal burns. Split-aperture irradiation using a modified HIFU transducer with six sectors and a smaller F number reduces the severity of skin burns, and thus will improve the safety of HIFU therapy