Coagulation of swine liver and canine prostate with a prototype split-focus transducer

The split-focus approach has a potential to substantially improve the throughput of coagulation HIFU treatment. A prototype split-focus transducer with two elements at 4.3 MHz combined with a small imaging probe at 6.5 MHz was constructed for transrectal treatment of a prostate. Computer simulation predicted that a coagulation volume approximately three times larger than single-spot focus would be obtained with split focus. Swine liver lobes were intraoperatively insonated for 4 s at a peak intensity of 850 W/cm². A lesion of coagulative necrosis three to six times larger than single-spot focus in volume was formed with the split focus. A canine prostate was then transrectally treated. A cavity, 0.35-0.45 cm³ in volume, was formed with only four shots of split-focus insonation.