Numerical simulations of improved compensation of masking strain-induced motions of scatterers in contact-mode optical coherence angiography
Alexey A. Zykov,1 Lev A. Matveev,1 Alexander L. Matveyev,1 Vladimir Y. Zaitsev,1
1 Federal research center Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia
Abstract
Visualization of microvasculature in contrast-agent-free optical coherence angiography (OCA) is based on discrimination of moving blood particles against the surrounding “solid” tissues assumed to be motionless. In real situations, various natural motions of living tissues may strongly mask the detected blood flows. To suppress these masking motions various methods are used, combining physical immobilization of the examined tissue (for example, using special windows in experiments with mice) with special signal processing to compensate the masking motions. In non-contact OCA the masking motions are mostly related to translational axial displacements of the tissue. For essentially sub-wavelength inter-scan displacements, such motions can be fairly easily compensated by estimating depth-averaged phase variation between the compared A-scans. However, if the A-scans belong to different B-scans, the motion amplitudes may be too big and cannot be efficiently compensated, which is a typical situation for OCA application on patients. In such cases contact mode can be used to suppress such strong displacements typical of non-contact mode. However, in the contact mode the pressure of the OCT-probe produces in the tissue depth-dependent straining. Its compensation requires more complex processing in comparison with translational axial displacements, but still can be fairly efficient for sub-wavelength strain-induced displacements using straightforward compensation of unambiguously estimated depth-dependent displacement. For stronger strains, the phase wrapping introduces ambiguity in the estimation of displacements, such that after simple (even depth-dependent) phase-correction such masking motions still noticeably degrade the microvasculature images. In this study an improved variant of compensation of strain-induced masking motions is proposed and demonstrated using numerical simulations, in which blood flows and various types of masking motions (translational and strain-induced) with various amplitudes can readily be imitated.
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Alexey Zykov
IAP RAS
Russia
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