基于凸阵列超声换能器的宽波束成像算法研究

Implementation of Wide-Beam Ultrasound Imaging Based on a Convex Transducer

超声宽波束成像是一种高帧频超声成像技术,相对于线聚焦、平面波和发散波等成像方法,其通过远点聚焦能更好地平衡图像分辨率、对比度和帧频等成像性能。目前,宽波束成像的主要研究均是基于线阵超声换能器,但线阵超声换能器成像视野有限且不适用于较深的腹部器官。本研究基于凸阵列超声换能器研究宽波束成像算法,评估凸阵列下宽波束成像方法的性能。基于128阵元的凸阵列换能器,在软件仿真平台和真实实验两种环境分别实施宽波束成像,得到原始的通道数据后,采用延时叠加的方法对仿真和实验数据进行波束合成,建立宽波束超声影像;针对图像的对比度与空间分辨率,将宽波束成像结果分别与传统的聚焦成像、复合发散波成像等方法进行定量的比较分析。相对于复合发散波成像,宽波束成像具有更高的图像对比度(仿真情况下为19.6 dB,提高了67.1%;实验情况下为19.1 dB,提高了33.1%),但其空间分辨率在仿真和实验中有不同的表现。在50~90 mm深度范围内,仿真情况下宽波束的平均分辨率为1.11 mm,相对发散波成像提升了18.1%;而在实验情况下62 mm处的分辨率为1.48 mm,相对降低了15.4%。综合结果表明,宽波束成像性能优于复合发散波成像。相比于聚焦扫描成像,宽波束成像具有更均匀的成像分辨率和更高的帧频。在凸阵换能器上,相比发散波成像方法和传统聚焦成像方法,超声宽波束成像方法具有更均衡的成像性能,可为临床应用特别是腹部超声提供更优的成像策略。

Ultrasound wide-beam imaging is a high frame rate ultrasound imaging method that can better balance several important imaging properties such as image spatial resolution,contrast ratio,and frame rate,which is implemented by putting the transmitting focus point far away from the actual imaging depth when compared to the traditional line-by-line scanning,plane and diverging wave imaging methods.Current studies on ultrasound wide-beam imaging are only based on linear array ultrasound transducers that have a limited imaging field of view and are not suitable for imaging of deep tissues and organs.In this paper,we investigated the wide-beam imaging algorithm based on a convex array ultrasound transducer and evaluated performance of the wide-beam imaging method with convex linear array.With a convex array transducer with 128 arrays,wide-beam imaging was implemented in two environments,a simulation platform and a real experiment scenario.The original channel data were first collected in both scenarios and then a delay and sum method was used to beamform and reconstruct the wide-beam ultrasound images.Quantitative analysis was performed in terms of the image contrast and spatial resolution and compared with the traditional focused line-by-line scanning,the diverging wave imaging methods.Compared with compound diverging wave imaging,the wide-beam imaging had higher image contrast(simulated case:19.6 dB,increased by 67.1%;experimental case:19.1 dB,increased by 33.1%),but its performance on resolution was different in the simulated and experimental cases(spatial resolution in the simulated case:1.11 mm,increased by 18.1%;in the experimental case:1.48 mm,decreased by 15.4%).Overall,the wide-beam imaging had better performance than compound diverging wave imaging.In comparison with the focused line-by-line scanning,wide beam imaging exhibited more uniform imaging resolution and a higher frame rate.This study implemented the wide-beam ultrasound imaging based on a convex imaging transducer for the first time and validated that the imaging method had more balanced imaging performance than the diverging wave imaging methods and traditional focused method,which offered a better imaging strategy for some relevant clinical applications,especially for the abdominal ultrasound.