High resolution ultrasonic imaging based on frequency sweep in both of transducer element domain and imaging line domain

Abstract

We developed the super resolution FM-chirp correlation method (SCM) and its high frame rate version called synthetic aperture-SCM (SA-SCM) based on frequency sweep in order to improve the range resolution in ultrasound imaging. However, in these methods, discontinuities in the lateral direction tend to occur, because the SCM processing is performed line by line in the image. In addition, in array transducers, grating lobes are more likely to occur when the spatial resolution is increased using high-frequencies. Therefore, another version called SCM-weighted SA was proposed. In the SCM-weighted SA, in order to avoid the lateral discontinuities, first the SCM processing is performed on each echo received by each transducer element, and then the obtained SCM result is used as a weight for SA processing. The SCM-weighted SA can generate multiple B-mode images each of which corresponds to each carrier frequency, and the appropriate low frequency images among them have no grating lobes. While this plurality of B-mode images can be used as multi-frequency images, it can also be integrated as one high SNR image. In the present study, we propose a method to generate the integrated one B-mode image by applying SCM again in the line direction of the obtained multi-frequency images, which is called SCM-weighted SA-SCM. This method can further improve the range resolution.