"Synthetic axial acquisition" full resolution C-scan ultrasonic imaging
This work relates to efficient and low cost acquisition of beamformer data for C-Scan imaging. In our previously described Directly Sampled In-phase and Quadrature (DSIQ) approach , as few as one complex sample per array element is used. In the 'Synthetic Axial Acquisition' (SAA) approach presented here, we take advantage of the fact that we use an unfocused transmit beam (plane wave) and are imaging primarily shallow and slowly moving, or static, tissue regions. Over a set of approximately 80 serial transmit / receive firings, each with the receive sampling trigger delay offset by the equivalent of one digital sampling interval, a per channel data record of sufficient length to enable a high quality approximation to conventional delay and sum beamforming using full length channel data records. Depending on the choice of beamforming condition, (center frequency, aperture size and focal depth), the SAA approach yields an approximately 30% improvement in lateral resolution over that achievable with DSIQ. FIELD II based simulations were performed for parameters appropriate for our next generation of 'Sonic Window' DSIQ-based C-Scan imaging system with a 5 MHz Center Frequency, 60 × 60 fully sampled 2D array and a 0.3 mm pitch. (A 1D array simulation was performed in the analyses presented here.) These simulations, which include analysis of the effects of target motion in both the parallel and perpendicular directions with respect to the acoustic beam, indicate that the approach is robust with respect to expected levels of target motion. The SAA approach partially precludes an opportunity for signal averaging that is afforded by the DSIQ approach. However, since the phase coherency of acquired SAA signal samples are accounted for in the beamforming summation, the impact on final image SNR is modest. © 2005 IEEE.