摘要:
为了分析医学超声在非均匀组织中的分布特性,建立了超声发射声场的计算模型。采用交错网格有限差分法对耦合超声非线性方程进行数值求解,获得了声速、密度及非线性参数非均匀分布情况下人体腹壁组织内的超声声场分布数据。同均匀介质相比:当声速均匀而密度非均匀时,声束仍聚焦良好,焦点处声能下降了1.8 dB;当密度均匀而声速非均匀时,声束发散严重,焦点处声能下降了3.8 dB,下降程度与非均匀组织接近。组织声速在空间分布的非均匀性是导致聚焦声束能量分布畸变的主要原因。
Abstract:
A numerical model is developed to simulate the acoustic field in heterogeneous tissue from a medical linear transducer. The coupled full-wave equation for nonlinear ultrasound is solved using a staggered grid finite difference time domain method. The distribution of acoustic pressure and power in human abdominal wall with heterogeneities in sound speed, density, and nonlinear parameter are obtained. Compared with homogeneous medium, when sound speed in tissue is uniform and density unchanged, the acoustic energy decreases only 1.8 dB in the focM region; when density in tissue is uniform and sound speed unchanged, the energy decreases 3.8 dB in the focal region, which is almost the same as heterogeneous tissue. Thus, the primary factor of the aberration of focused beam is the heterogeneous distribution of the tissue sound speed.
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