Ultrasonic virtual source imaging base on adaptive bi-directional point-wise focusing

Ultrasonic virtual source imaging based on adaptive bi-directional point-wise focusing is proposed to improve the resolution and contrast when the depth increases. Firstly, ultrasonic array is divided into sub-arrays, the ultrasonic RF scanning lines are collected using fixed-focusing transmitting and receiving and these focuses are considered as virtual sources. Secondly, these scanning lines are point-wise focused using adaptive weighting, and then high-quality image is obtained. Simulations for point and speckle targets are used to verify this algorithm. 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 quality of images at different depths are consistent and equal to that of fixed-focus transmitting and dynamic receiving algorithm based on 64-channel imaging system. The experiment results prove that the image is much clearer on the whole by the proposed algorithm.