IEEE Trans Ultrason Ferroelectr Freq Control. 2018 Jul;65(7):1125-1132. doi: 10.1109/TUFFC.2018.2830108.
It has been well known that the treatment time of high-intensity focused ultrasound (HIFU) surgery can be reduced by expanding the focal area per sonication. Previously, a dual-concentric transducer using phase-inverted signals was proposed to axially extend the focal area, but it has suffered from the deep notch point between two focal lobes. In this paper, we propose the improved HIFU transducer with dual-concentric aperture driven by phase-inverted multifrequency signals based on an inversion layer technique. The proposed transducer can generate the expanded focal zone with a significantly reduced level of the notch point between two focal lobes in the axial direction. The performance of the proposed transducer was investigated using finite element analysis simulation. The electrical impedance, one-way impulse response, and acoustic field of the transducer were simulated. Subsequently, the lesion volume was investigated by heat transfer simulation. In the proposed method, the level of the notch point was increased above -6 dB due to various phase interactions between the fundamental and harmonic frequency combinations and the inverted and noninverted frequency combinations. The -6-dB depth of field related to the necrotic lesion size was increased by 141% compared with the conventional single element transducer. Thus, the proposed transducer can be a potential way to enlarge coagulated lesion size resulting in a reduced overall treatment time of HIFU surgery.
众所周知，通过扩大每次超声辐照的焦域面积可以缩短高强度聚焦超声（HIFU）手术的治疗时间。此前，已经提出了一种使用相位反转信号的双同心换能器来轴向扩展焦域，但它存在两个焦域之间存在深的凹口问题。在本文中，我们提出了一种基于反转层技术的改进型双同心孔径相控阵 HIFU 换能器，该换能器可以在轴向产生扩展的焦区，同时显著降低两个焦域之间凹口的深度。使用有限元分析模拟研究了所提出的换能器的性能。模拟了换能器的电特性、单程脉冲响应和声场。随后，通过传热模拟研究了损伤体积。在提出的方法中，由于基波和谐波频率组合以及反转和非反转频率组合之间的各种相位相互作用，凹口的电平增加到了-6dB 以上。与传统的单阵元换能器相比，与坏死性损伤尺寸相关的-6dB 焦深增加了 141%。因此，所提出的换能器可以成为一种潜在的方法来扩大凝固性损伤的尺寸，从而缩短 HIFU 手术的整体治疗时间。
