Fig. 2.

Resolution and signal-to-noise ratio (SNR) comparison. (a) Lateral resolution versus axial position. Solid curve: fitting by Gaussian beam formula. (b) Expected lateral resolution versus axial position of contour (blue dashed line), $z$-stack (red dashed line), and raster scan (gray dotted line) based on the fitted data in (a). (c) Acoustic-amplitude SNR versus axial position for raster scan. (d) Expected acoustic-amplitude SNR versus axial position of contour, $z$-stack, and raster scans based on the fitted data in (c).