Figure 2

Demonstrations of angular compounding and digital focusing by using the agar phantom containing 1 μm PS beads. (a) Eleven angles, [−4.0°, −3.2°, −2.4°, −1.6°, −0.8°, 0°, 0.8°, 1.6°, 2.4°, 3.2°, 4.0°], whilst imaging the same area, and the composite image created by directly overlapping the 11 angular OCT images is entirely mismatched. Twenty B-scans are taken for every angle to reduce random noises. (b) The angular compounded image is produced by fusing the correctly registered angular images. (c) With digital focusing, the composite image presents better horizontal resolution and deeper penetration. (d) The image composed of 220 B-scans (20 × 11) by a normal OCT system is used as a control group. (e) The reduction in the background standard deviation (STD) versus the number of angles for AC and AC + DF. In the normal OCT, the data is captured at zero angle 11 times. The regions for STD calculations are marked by the blue rectangles in (b–d). (f) The contrast varies with depth, and Z is the vertical distance to the sample surface. (g) The zoom-in views of the red rectangles in (b–d) show three adjacent beads close to the focal plane and their intensity profiles along the horizontal direction (on the linear scale). (h) The zoom-in views of the yellow rectangles in (b–d) show several beads away from the focal plane. AC, angular compounding; DF, digital focusing; STD, standard deviation. Scale bar, 200 μm in (a–d), 50 μm in (g,h).