变厚度聚焦换能器对声焦域轴向长度影响的研究*

针对不同厚度的病变组织,改变声焦域轴向长度能提高高强度聚焦超声在临床治疗过程中的安全性和有效性。基于多频超声波叠加原理,该文提出了变厚度(多频)聚焦换能器,并设计了两种类型变厚度聚焦换能器。根据瑞利积分法推导了变厚度聚焦换能器声场,计算和分析了变厚度聚焦换能器的声焦域轴向长度,并与等厚度(单频)聚焦换能器声焦域轴向长度进行对比。结果显示,变厚度聚焦换能器中心到边缘的厚度变化趋势与声焦域轴向长度变化相关,中间薄两边厚换能器声焦域轴向长度缩短,中间厚两边薄换能器声焦域轴向长度变长,且实验验证了理论的正确性。研究结果可为变厚度聚焦换能器声场研究和高强度聚焦超声的临床治疗提供参考。

Research on the influence of variable thickness focusing transduser on the axial length of acoustic focal region

For different thickness of diseased tissue, changing the axial length of the acoustic focal region can improve the safety and effectiveness of HIFU in clinical treatment. Based on the multi-frequency ultrasonic superposition principle, a variable thickness (multi-frequency) focusing transducer is proposed in this paper, and two types of variable thickness focusing transducers are designed. According to the Rayleigh integral method, the sound field calculation method of variable thickness focusing transducer is derived, the axial length of the acoustic focal region of the variable thickness focusing transducer is calculated and analyzed, and it is compared with the axial length of the acoustic focal region of the equal thickness (single frequency) focusing transducer. The results show that the thickness variation trend from the center to the edge of the variable thickness focusing transducer is related to the axial length variation of the acoustic focal region, the axial length of the acoustic focal region of the transducer which is thin in the middle and thick on both sides is shortened, the axial length of the acoustic focal region of the transducer which is thick in the middle and thin on both sides becomes longer, and the theoretical correctness is verified by experiments. The research results can provide reference for the research of sound field of variable thickness focusing transducer and clinical treatment of HIFU.