超声虚源成像中自适应双向空间逐点聚焦方法

针对传统超声成像中图像分辨率和对比度随深度下降的问题,提出了一种基于虚源的自适应双向空间逐点聚焦超声成像方法。首先,使用超声换能器线列阵分子孔径分别定焦点发射和接收超声波,采集扫描线数据;然后将焦点视为虚拟点声源,计算虚源到空间成像点的延时,利用合成孔径原理再次进行空间逐点聚焦;在合成过程中采用相干系数进行自适应加权。采用空间脉冲响应法对不同深度的点目标和囊目标仿真成像,从而量化分辨率和对比度。在F数为1.5、焦距为10 mm时(对应子孔径阵元数为17)可以获得与64通道定焦点发射、动态聚焦接收相当的图像质量且在所有深度上保持一致。实际硬件平台的体模成像实验进一步验证了方法的有效性。该方法可在整个成像深度范围内保持和常规成像一致的分辨率和对比度,从而获得更优的整体成像效果。 

Adaptive bi-directional point-wise focusing method in ultrasonic imaging based on virtual source

Adaptive bi-directional point-wise focusing method in ultrasonic imaging based on virtual source is proposed to improve the resolution and contrast when the depth increases. Firstly, the ultrasonic transducer array is divided into sub-arrays and the ultrasonic RF scanning lines are collected using fixed-focus transmitting and receiving method. Secondly, these focuses are considered as virtual sources and the time delays between these virtual sources and the spatial points are calculated. The ultrasonic scanning lines are point-wise focused again using synthetic aperture method and weighted by the adaptive coherence factor. Then the high-quality image is obtained. Simulations based on spatial impulse response theory are used to verify the method. The imaging simulations for point and speckle targets are used to quantify the resolution and contrast. It proves that when the F number is 1.5 and the focus is at 10 mm (such a sub-aperture corresponds to only 17 elements of array), the imaging qualities at different depths are consistent for the proposed method and equal to that of fixed-focus transmitting and dynamic depth receiving method based on 64-channel imaging system. The phantom imaging experiment proves that the proposed method can obviously improve the imaging quality. The consistent resolution and contrast of the conventional imaging system can be obtained at all imaging depths and the image is much clearer on the whole.