半球形高强度聚焦超声相控换能器的仿真研究

Simulation Study on Hemispherical Phased Array Transducer for High Intensity Focused Ultrasound

大开口半球形相控换能器能够最大化覆盖颅骨表面,使超声能量尽可能多地穿越颅骨到达治疗靶区,从而避免颅骨处能量沉积。该文基于人体头颅结构建立三维高强度聚焦超声(HIFU)经颅传播模型,利用时域有限差分法(FDTD)结合Westervelt声波非线性传播方程和Pennes生物热传导方程进行温度场数值仿真,首先研究小开口换能器的阵元信号激励频率、激励面积比、阵元半径和阵元数对其形成温度场的影响及变化规律,其次将这些规律应用于大开口换能器,并对其形成温度场特性进行研究。小开口换能器结果表明,在一定频率范围内,焦域中心温度随激励频率增加而升高,而54℃以上区域长轴长逐渐减小,短轴长基本无变化;激励总功率一致时,激励面积比越大,焦域中心温度越高,54℃以上区域长轴、短轴较长;使用小开口直径换能器模型筛选的阵元激励频率和激励面积比可应用于设计大开口换能器,为大开口换能器的开发提供结构参数。

The hemispherical phased array transducer with a large-aperture can maximize coverage of the skull surface and allow the ultrasonic energy through the skull as much as possible to reach the treatment target,thus avoiding energy deposition at the skull.In this paper,the three-dimension transcranial propagation model of the high intensity focused ultrasound is established based on the human skull structure,the Westervelt nonlinear acoustic wave propagation equation and Pennes biological heat conduction equation are used to simulate the temperature field by the finite difference time domain（FDTD）.First,the influences of the excited frequency of the array element,incentive area ratio,elements radius and numbers of small-aperture transducer on the temperature filed are investigated.Then,the results obtained are used to study the characteristics of temperature filed of transducer with large-aperture.The simulation results of small-aperture transducer demonstrate that the temperature of the focal region center is increased with increase of the excited frequency in a certain frequency range and the length of the long axis is decreased gradually while the length of the short axis is invariable at the area of above 54℃.When the incentive power is a constant value,the greater the excitation area ratio,the higher the center temperature of the focal region,and the length of long axis and short axis are longer at the area of above 54℃.The excited frequency of the array element and the excitation area ratio obtained from the small-aperture transducer model can be applied to design the large-aperture transducer and provide structure parameters for developing the large-aperture transducer.