Dual concentric-sectored HIFU transducer with phase-shifted ultrasound excitation for expanded necrotic region: a simulation study.

In high-intensity focused ultrasound (HIFU) surgery, it is desirable to produce a large necrotic area per sonication for reduced treatment time. It has been well known that the conventional split-focus scheme capable of generating multiple foci can increase a necrotic region in the lateral or elevational direction. To treat a deep-seated target, it is necessary to generate an expanded necrotic region in the axial direction. In this paper, a novel sonication scheme capable of producing an expanded coagulated region in the both lateral and axial directions is presented. The proposed method can generate multi-focal spots in the lateral and axial directions by using a dual concentric-sectored (DCS) HIFU transducer based on phase-shifted ultrasound excitation. A sound field simulation was employed for this investigation. Four electrical signals with identical center frequencies and different phases activated the DCS transducer, composed of a disc and an annular element with a confocal point. Four 4-MHz ultrasound signals with different phases were transmitted to the target simultaneously, resulting in generation of dual-focal spots in the lateral and axial directions. The sound field simulation results showed that the 0-6-dB lateral and axial beamwidths of the DCS transducer were maximally 79% and 91% broader than the single-element transducer. Subsequently, bio-heat transfer and thermal dose simulation results were matched to the sound field simulation. Hence, the DCS HIFU transducer combined with phase-shifted excitation may be a promising approach to treat a deep-seated target and to reduce treatment time for HIFU surgery.