A clinical study of adaptive beamforming using time-delay adjustments on a 1-D array
Time-delay estimation is made using echoes from a user-selected target region, to which the transmit focus is applied to maximize signal coherence. The estimated time-delay profile is split into 2 components using a least-squares fitting: one component indic ates an effective speed of sound, while the other is the residual time -delay error. On subsequent transmit and receive beamforming, the compensation can be made using the first component through modifying normal beamforming calculations, or, in addition, with the second component applied as well. These modifications were made in near real-time on the Elegra™, and were used to perform breast scanning on 7 patients. Images from the clinical scanning will be presented, along with the corresponding channel data and the estimated time-delay profiles. The results indicate that the compensation scheme resulted in significant improvement in image quality in some cases, while in some other cases, the effect is weak or unstable. One of the causes is that the selected target region may contain a cluster of a few strong scatterers and exhibit complex scattering signatures that are mistaken as propagation distortion. Other causes include the isoplanatic patch size, the elevation dimension of each array element, and the limitation of time -delay correction. These causes will be demonstrated using data obtained from clinical scanning and phantom measurements.