Clear 3D Images
An optical beam is directed at the tissue, and a small portion of this light that reflects from sub-surface features is collected. Note that most light is not reflected but, rather, scatters off at large angles.
In conventional imaging, this diffusely scattered light contributes to a background that obscures an image. However, in OCT, optical coherence is used to record the optical path length of received photons allowing rejection of most photons that scatter multiple times before detection.
The OCT can build up clear 3D images of thick samples by rejecting background signals while collecting light directly reflected from surfaces of interest.