Advantages of split-focus approach in coagulation therapy

A most critical problem in the coagulation therapy with a single-spot focus is that the hot spots formed in tissue tends to migrate from the focal zone towards the transducer when the ultrasonic power deposition is higher than the optimum. The authors found that the split-focus approach is effective for improving the throughput of ultrasonic coagulation therapy not only due to its large heating pattern but also through preventing this hot-spot problem. The tissue temperature distribution during split-focus exposure was analyzed using some approximation. The temperature at the central acoustic zero in the split focus reaches the spatial peak within the order of a second after the start of the exposure, when the focused transducer has an F-number of around one and an ultrasonic frequency higher than the order of a megahertz. The problem above can be prevented in this approach because the hot spots may be created only near the acoustic zero