  Multiple scattering is one of the main factors that limits the penetration
depth of optical coherence tomography (OCT) in scattering samples. We propose a
method termed multi-focus averaging (MFA) to suppress the multiple-scattering
signals and improve the image contrast of OCT in deep regions. The MFA method
captures multiple OCT volumes with various focal positions and averages them in
complex form after correcting the varying defocus through computational
refocusing. Because the multiple-scattering takes different trajectories among
the different focal position configurations, this averaging suppresses the
multiple-scattering signal. Meanwhile, the single-scattering takes a consistent
trajectory regardless of the focal position configuration and is not
suppressed. Hence, the MFA method improves the signal ratio between the single-
and multiple-scattering signals and improves the image contrast. A scattering
phantom and a postmortem zebrafish were measured for validation of the proposed
method. The results showed that the contrast of intensity images of both the
phantom and zebrafish were improved using the MFA method, such that they were
better than the contrast provided by the standard complex averaging method. The
MFA method provides a cost-effective solution for contrast enhancement through
multiple-scattering reduction in tissue imaging using OCT systems.
