Fig. 1.

Graphical illustration of signal blurring in the out-of-focus regions in AR-PAM. (a) Distorted shapes of the PA signals (blue dashed lines) above and below the focal plane. Black solid lines: acoustic detection field. Red circle: the imaging target. (b) Concave shape of the signal blurring when the target is located above the focal plane. (c) Convex shape of the signal blurring when the target is located below the focal plane. PAi: detected PA signal when the UST is at position Pi; i = 1, 2, 3. (d) Comparison between imaging targets and their corresponding signals in a B-scan image. The targets are arranged at different depths from the focus.