27 April 2016 Optimization of phase-variation measurements in low-coherence methods: implications for OCE
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Phase-resolved measurements found numerous applications in low-coherence methods, in particular in OCT-based compressional elastography, where phase-variation gradients are used for estimating strains produced by the OCT probe pressed onto the tissue. Conventionally, for the reference and deformed pixelated OCT scans, one performs comparison of phases taken from pixels with the same coordinates. This is reasonable in regions of sufficiently small sub-pixel displacements, for which the so-compared pixels contain the same scatterers. Furthermore, to avoid error-prone multiple phase unwrapping for reconstructing displacements, one have to ensure even smaller sub-wavelength displacements. This limits the allowable strains to less than ~10-4-10-3, although such weak phase gradients can be strongly corrupted by measurement noises. Here, we discuss how creation of an order of magnitude greater strains can be used for increasing the signal-to noise ratio in estimating phase gradients by obviating the phase-unwrapping procedures and reducing the influence of decorrelation noise for supra-pixel displacements. This optimized phase-variation measurement makes it possible to perform strain mapping in optical coherence elastography with exceptionally high tolerance to noises due to possibility of using significantly increased strains. We also discuss the effect of “frozen-phase zones” associated with displaced strong scatterers. This effect can result in appearance of artifacts in the form of false stiff inclusions in elastograms in the vicinity of bright scatterers in OCT scans. We present analytical arguments, numerical simulations and experimental examples illustrating the above-mentioned features of the “frozen-phase” effect and advantages of using the proposed optimized phase-variation measurement with pixel-scale displacement compensation in the compared OCT scans.
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Vladimir Yu. Zaitsev, Vladimir Yu. Zaitsev, Alexandr L. Matveyev, Alexandr L. Matveyev, Lev A. Matveev, Lev A. Matveev, Grigory V. Gelikonov, Grigory V. Gelikonov, Alexander A. Sovetsky, Alexander A. Sovetsky, Alex Vitkin, Alex Vitkin, "Optimization of phase-variation measurements in low-coherence methods: implications for OCE", Proc. SPIE 9887, Biophotonics: Photonic Solutions for Better Health Care V, 98871G (27 April 2016); doi: 10.1117/12.2228093; https://doi.org/10.1117/12.2228093

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