  Displacement estimation in optical coherence tomography (OCT) imaging is
relevant for several potential applications, e.g. for optical coherence
elastography (OCE) for corneal biomechanical characterization. Larger
displacements may be resolved using correlation-based block matching
techniques, which however are prone to signal de-correlation and imprecise at
commonly desired sub-pixel resolutions. Phase-based tracking methods can
estimate tiny sub-wavelength motion, but are not suitable for motion magnitudes
larger than half the wavelength due to phase wrapping and the difficulty of any
unwrapping due to noise. In this paper a robust OCT displacement estimation
method is introduced by formulating tracking as an optimization problem that
jointly penalizes intensity disparity, phase difference, and motion
discontinuity. This is then solved using yynamic programming, utilizing both
sub-wavelength-scale phase and pixel-scale intensity information from OCT
imaging, while inherently seeking for the number of phase wraps. This allows
for effectively tracking axial and lateral displacements, respectively, with
sub-wavelength and pixel scale resolution. Results with tissue mimicking
phantoms show that our proposed approach substantially outperforms conventional
methods in terms of axial tracking precision, in particular for displacements
exceeding half the imaging wavelength.
