Two-Stage Beamforming for Phased Array Imaging using the Fast Hankel Transform

An ultrasound scan generates a huge amount of data. To form an image this data has to be transferred to the imaging system. This is an issue for applications where the data transfer capacity is limited such as hand-held systems, wireless probes and miniaturized array probes. Two-stage beamforming methods can be used to significantly reduce the data transfer requirements. In the first stage, which is applied in-probe, the amount of data is reduced from channel to scanline data. In the imaging system the data is then beamformed to obtain images that are synthetically focused over the entire image. Currently two approaches exist for the second stage. The first approach is a time-of-flight approach called synthetic aperture sequential beamforming (SASB) that has been developed for both linear and phased arrays. SASB does however introduce artefacts in the image that can be reduced by tapering the first stage scan lines at the cost of lateral resolution. The second approach is based on the wave equation, but a computationally efficient method for phased arrays that is producing sector scan data is lacking. Here we propose an algorithm that uses the fast Hankel transform to obtain a fast algorithm. The imaging performance of this method is evaluated with simulations and experiments. Compared with PSASB, which is an adaption of SASB for phased arrays, our method requires a similar amount of operations to construct the entire image and there is no trade-off between resolution and artefacts. These results show the advantage of using the wave equation instead of a time-of-flight approach.