激励声束聚焦形状对剪切波速度估计的影响

The Impact of Focal Configuration of Excitation Beam on Shear Wave Speed Estimation

为了探究运用现有的激励及检测技术实现区域弹性成像的可行性,以及在声辐射力脉冲激励下,聚焦形状、检测点的空间位置等因素对局部剪切波速度估算的影响,运用Filed Ⅱ以及有限元方法对声辐射力及组织响应情况进行了研究,并选用时域互相关方法对局部剪切波速度进行估计.结果表明,随着检测灵敏度的提高,可以实现发射2～3次激励脉冲即可对检测组织进行区域成像;使用现有的剪切波速度估计方法,浅表处与焦点深度处的剪切波速度估计值相差可达12.7％;f-number（聚焦深度/孔径）增大,可以增大成像面积,但是剪切波速度估计的准确性降低.鉴于此,提出波速修正算法,修正后波速估计值更接近理论值.以f-number为1.3为例,修正后的平均误差由3.2％降至0.6％.结果证明,现有的声辐射力激励及修正后的剪切波速度估计方法可用于区域弹性成像.

The aim of this work is to explore the feasibility of a large-scale elastography with the existing methods,and the impact of some factors such as focal configuration and detection position,on the estimation of local shear wave speeds under the same acoustic radiation excitation.Simulation program Field Ⅱ and finite element methods were used for the simulation of acoustic radiation force and tissue response,then a crosscorrelation based method was used for the estimation of local shear wave speed.Results showed that with the improvement of detection sensitivity,it was feasible for two or three excitation impulses to complete a shear wave speed image.The estimated shear wave speeds calculated with the existing methods were closely related with the spatial location of the detecting point; the difference was 12.7％ between the shear wave speeds measured at superficial locations and at focal depth.The imaging area was enlarged with the increase of fnumber （focal depth/aperture size）,however,the accuracy of shear wave speed estimation was reduced in the meantime.Thus,a modified algorithm was presented in the paper.After modification,the local shear wave speed is closer to the theoretical value; in the case of f-number was 1.3,the root-mean-square error was reduced from 3.2％ to 0.6％.It is demonstrated that the existing excitation of acoustic radiation force and the modified estimation method of shear wave speed can be used in large-scale elastographies.