Phase-aberration correction using near-field signal redundancy: correcting phase aberrations caused by medium-velocity and array-pitch errors

Phase aberration is one of the important factors which limit improvement to the lateral resolution of ultrasound imaging systems. Several methods have been developed during the last decade to correct for phase aberration errors. Recently, we have developed a near-field signal-redundancy algorithm and have tested it successfully on phantom and in vivo tissue data. In this algorithm, common midpoint signals are dynamically corrected before they are cross-correlated for phase-aberration measurement. This dynamic correction can reduce the difference between common midpoint signals caused by the near-field effect. The values of the array pitch and the average velocity in the medium, which are used in the dynamic near-field correction as well as in the image-formation process, are subject to errors. In this paper, the influences of these errors on the near-field signal redundancy algorithm and the image formation process are analyzed. It is found that the aberration profile derived from incorrectly assumed average velocity and pitch values can be used to correct for the phase aberration caused by velocity and pitch errors in the image formation process. It highlights the important role of the dynamic near-field correction in the signal-redundancy algorithm for targets in the near field.