经颅超声聚焦方法和声场特性研究

基于高分辨的CT数据建立了非均匀颅骨仿真模型,该模型引入了颅骨的声衰减系数,深入研究和分析了声波时间反转法和超声相控阵法在颅脑中的聚焦方法及效果。颅骨具有较强的声波衰减特性,使用时间反转聚焦时需要进行幅度补偿,对于0.7MHz的频率信号,幅度补偿后的时间反转聚焦声场主瓣宽度窄、旁瓣低,焦点处声场比无幅度补偿的时间反转法提高8.86dB,比超声相控阵聚焦法提高7.89dB,具有很好的空间聚焦精度和聚焦效率。研究了颅骨衰减系数、声场焦点位置、声波频率、换能器阵列位置和方位等参数对聚焦声场的影响,结果表明,幅度补偿时间反转法比相控阵法具有更低的旁瓣,且高频时的聚焦效果比相控阵好,相控阵聚焦对换能器阵列的位置和方位比较敏感,而时间反转经颅超声聚焦对声传播路径和入射角具有更高的鲁棒性。 

Research on focusing methods and sound field characteristics of transcranial ultrasound focusing

A heterogeneous cranial simulation model is established based on high-resolution CT data, which introduces the acoustic attenuation coefficient of the cranium, and the focus methods and effects of time reversal method of acoustic waves and ultrasonic phased array method in the skull are studied and analyzed. The skull has strong acoustic attenuation characteristics and requires amplitude compensation when using time-reversal method. For a frequency signal of 0.7MHz, the amplitude compensated time-reversal focused acoustic field has narrow main flap width and low flap amplitude, and the acoustic field at the focal point is 8.86dB higher than that of the time-reversal method without amplitude compensation and 7.89dB higher than that of the ultrasonic phased-array focusing method, which has good spatial focusing accuracy and focusing efficiency. By studying the effects of skull attenuation coefficient, sound field focal position, acoustic frequency, transducer array position and orientation on the focused sound field, it was shown that the amplitude compensated time-reversal method has lower partials than the phased array, and the focusing effect at high frequencies is better than the phased array method, the phased array method is more sensitive to the transducer array position and orientation, while the time-reversal transcranial ultrasound focusing has higher robustness to the sound propagation path and incident angle. The time-reversed transcranial ultrasound focusing has higher robustness to acoustic propagation path and incident angle.