Adaptive selection of spatial scale to estimate axial gradients of inter-frame phase variations for mapping strains in optical coherence elastography

This paper introduces an adaptive method that significantly improves visualization quality of reconstructed strains in phase-sensitive optical coherence elastography (OCE). The strain is estimated by finding axial gradients of interframe phase variations and the phase-variation gradients are estimated over a certain scale. The noise level of the so-found strain maps heavily depends on the chosen scale that is used for gradient estimation. Choosing a scale that is too small or too large can degrade the results of elastographic visualization. In real conditions the spatial strain distribution usually is essentially inhomogeneous. Obtaining the best results in different areas of OCT scans requires utilization of different scales, although usually some fixed "compromise" scale over the entire OCT image is used to estimate phase-variation gradients. To improve the quality of strain maps in phase-sensitive OCE, we propose a method of automatic adaptive selection of this scale depending on the level of local strain in the visualized area. The proposed method is elucidated using on both numerically simulated and real OCT scans which are characterized by significant spatial inhomogeneity of strains.