Fig. 3.

Homogeneous phantom simulation. (Top row) Estimated average sound speed map by (left) CF maximization with direct pixel-to-pixel comparison and with 1D (middle) and 2D (right) registration corrections. The red ‘X’ symbols on the left image show pixels that were analyzed in the bottom two rows. Second row shows the point density map of the 1D and 2D location correction process. The color map is discrete with integer values. Rows 3–4 show CF profiles as a function of beamforming speed. In the case of direct comparison, each point in the profile corresponds to the same beamforming location. For 1D and 2D registration corrections, each point represents a different spatial location accounting for the signal drift. All three profiles intersect at 1540 m/s, the base beamforming speed.