Two-dimensional phase aberration correction using an ultrasonic 1.75D array: case study on breast microcalcifications

Ultrasound phase aberration resulting from tissue velocity inhomogeneities reduce the focusing ability of ultrasound waves and degrade image quality. Two-dimensional phase aberration measurements and correction with higher-order 1.75D arrays are expected to reduce this problem. We implement a least-mean-squares measurement algorithm and discuss implementation decisions for phase aberration correction techniques. We present clinical results from using individual channel RF signals from an 8×128 1.75D array (Tetrad Co.) interfaced with a Siemens Elegra scanner. The average patient aberration measurement in the thyroid (9 patients) was 22.2±4.6 ns r.m.s. amplitude with 4.8 mm±1.3 mm FWHM autocorrelation length. Analysis of breast scans (8 patients) resulted in a patient average aberration measurement of 33.1±7.0 ns r.m.s. amplitude and 6.4±1.5 mm FWHM. The results show a statistically significant difference (p-value=0.01) in aberration measurements in clinical breast imaging patients in age groups 20-40 years old and 50-70 years old. We present results of receive-only aberration correction in clinical images and describe quantitative improvements and the results from using specific correction implementation techniques in a case study of breast microcalcifications after phase aberration correction.