声通道上的条状障碍物对高强度聚焦超声声场的影响

目的 研究高强度聚焦超声(HIFU)透过用条状障碍物模拟的肋骨后的声场分布.方法 引导HIFU声束透过肋间隙、肋缘及正对肋骨,在每种情况下将肋骨分别置于距焦平面3、6、9 cm处,采用水听器描绘出了每种情况下声场的分布.结果 轴向声压分布:在3种障碍物分布情况下,声通道上由于肋骨的存在,声压幅值较自由场下降了60%～80%,相对于自由场,-6 dB焦域的尺寸增大0.5～1.5 mm.焦点的位置相对于自由场,也发生了前移,焦点向换能器方向靠近0.1～2.3 mm.径向声压分布:在3种障碍物分布情况下,当肋骨距焦平面3、6 cm时,声压的分布出现多峰的现象,相对于自由场,声压幅值降低.当肋骨距焦平面9 cm时,在经过了肋骨之后,波束基本上还是保持了原来的形状,声压分布与自由场接近.结论 声通道上存在肋骨时HIFU焦域的声压幅值明显降低,声压幅值的降低与声束轴线与肋骨的相对位置以及肋骨距焦平面的距离有关.声通道上存在肋骨时对HIFU声焦域有影响,-6 dB焦域尺寸增加.

Effects of Simulated Rib-like Barrier in High Intensity Focused Ultrasound Beam Path on its Acoustic Field

Objective To investigate the effects of ribs in HIFU beam path on its acoustic field.Methods The beam axis directing through the intercostal space,at the rib edge and to the centre of middle rib in each case,the ribs were placed far away from the focal plane 3、6、9 cm respectively and the hydrophone plots were recorded to note the acoustic field distribution.Results The acoustic pressure distribution in axial:Because of the ribs in beam path,the acoustic pressure amplitude decreased 60%～80% compared with that in free field.When the ribs were placed in the beam path,-6 dB focal region increased 0.5～1.5 mm compared with that in the free field.The focus position relative to that in free field was close to the transducer about 0.1～2.3 mm.The acoustic pressure distribution in radial:When the ribs were placed 3、6 cm in front of the focal plane,the phenomenon of acoustic pressure distribution showed multiple peaks.Compared to that in the free field,acoustic pressure amplitude decreased.When the ribs were placed 9 cm in front of the focal plane,the beam maintained the original shape and acoustic pressure distribution was similar to that in the freefield.Conclusions The ribs in beam path lead to the acoustic energy attenuation.The attenuation of the energy was relative to the relative location between HIFU beam axis and the ribs,and the attenuation of the energy was relative to the ribs position from the focal plane.The ribs in HIFU beam path play great impact on the HIFU acoustic focal region (AFR),and the full width at half maximum (FWHM) increased.