声速不均匀介质热声成像的声场仿真

Sound field simulation for thermoacoustic tomography with acoustic speed heterogeneity

为了精确表示声速不均匀介质热声成像的声场,提出了一种时域有限差分(FDTD)仿真方法。先用FDTD将热声成像的基本方程离散化,给出描述热声成像的离散差分方程;再对电磁波脉冲进行两次修正,以消除高频电磁波引入的计算误差。计算机仿真研究的结果表明:当介质声速不均匀时,FDTD仿真方法其准确度高于目前常用的飞行时间法。在仿真实验条件下,当介质的声速差异大于50%时,FDTD法的误差比飞行时间法小十倍以上。可见,FDTD方法是一种有效的热声成像声场仿真方法,可以为声速不均匀介质热声成像算法的研究提供理论基础。

A finite-difference time-domain （FDTD） method is proposed to exactly calculate the sound field of the thermoacoustic tomography （TAT） with the inhomogeneous acoustic speed. Firstly, the basic equations of the TAT are discretized to differential equations by the FDTD. Then the electromagnetic pulse is modified twice in the simulation process in order to eliminate the error introduced by high frequency electromagnetic waves. It is shown by computer simulation results that the FDTD method has better accuracy than the time-of-flight method, which is in the common use, in the TAT with the inhomogeneous acoustic speed. When the acoustic speed difference is larger than 50%, the error of the FDTD method is ten times smaller than that of the time-of-flight method under the simulation condition. Therefore, this FDTD method is an efficient one for the sound field simulation of the TAT and can provide the theoretical basis for reconstruction algorithms of the TAT with the acoustic speed heterogeneity.