Resolution improvement of point targets by real-time phase aberration correction: in vivo results

Ten patients with suspected microcalcifications were scanned with a 9 MHz, 8×96 1.75D array transducer and Siemens Antares scanner. Aberration profiles were estimated by cross correlation of individual element echo signals using a least-squares algorithm over a 3×5 element neighborhood. Transmit and receive beamformer delays were modified to compensate for the estimated profile. Single video frames captured at times just before and just after application of aberration correction were compared. The apparent change in microcalcification width was estimated with sub-pixel precision by comparing upsampled image lines at a threshold of 80%. The average reduction in image width was 39.7%. The average brightness increase was only 1.9%. Offline processing of RF data captured on the same patients shows a pre-log compression increase in envelope amplitude of 39% after off-line aberration correction using the same algorithm. The relatively small improvement in brightness during online correction is due to logarithmic compression and video-saturation effects.