Fig. 4.

(a) Representative B-scan image of tissue phantom. The red, green, blue and purple crosses indicate the randomly selected positions (P1–P4). (b) The noise-free sample correlation coefficient | ${\rho }_s^{\prime }$(Δx)_{R to R+1}| is plotted as a function of the lateral shift. (b) The noise-free sample correlation coefficient | ${\rho }_s^{\prime }$(Δz)_{R to R+1}| is plotted as a function of the axial shift.