中文摘要：

针对经颅超声难以精确聚焦的问题，本文研究了基于虚拟源的时间反转方法，建立颅骨二维数字模型，在聚焦目标处设置虚拟声源，利用时域有限差分法模拟超声时间反转过程，并考察基于虚拟源时间反转方法的聚焦效果。数值仿真结果表明，基于虚拟源的时间反转方法可以实现经颅超声的精确聚焦，聚焦强度和精度好于传统的相控聚焦；换能器中心频率和数量对聚焦效果的影响规律与相控聚焦时类似；该方法可以同时向多个焦点聚焦，并自适应调节各焦点处声压幅度。

英文摘要：

To overcome the difficulty of ultrasound to accurately focus in the brain, a time reversal methodbased on virtual sources is studied in this article. A 2-D numerical model of human skull with virtual sourcesat the focusing targets is established. The time reversal process is simulated with finite difference time domainmethod, and the effectiveness of focusing with time reversal method is studied. The numerical simulation resultsshow that time reversal based on virtual sources can be used to control the focus of the ultrasound throughthe skull, with better precision than using traditional phase-control focusing method. The central frequencyand number of elements of the ultrasound transducer affect the focusing with similar patterns as in normalphase-control focusing. Moreover, the method allows for more than one target to be focused simultaneously,and the pressure amplitude at each focus can be adjusted adaptively.