Analysis of spatial resolution in phase-sensitive compression optical coherence elastography

Abstract

Optical coherence elastography (OCE) is emerging as a method to image the mechanical properties of tissue on the microscale. However, the spatial resolution, a main advantage of OCE, has not been investigated and is not trivial to evaluate. To address this, we present a framework to analyze resolution in phase-sensitive compression OCE that incorporates the three main determinants of resolution: mechanical deformation of the sample, detection of this deformation using optical coherence tomography (OCT), and signal processing to estimate local axial strain. We demonstrate for the first time, through close correspondence between experiment and simulation of structured phantoms, that resolution in compression OCE is both spatially varying and sample dependent, which we link to the discrepancies between the model of elasticity and the mechanical deformation of the sample. We demonstrate that resolution is dependent on factors such as feature size and mechanical contrast. We believe that the analysis of image formation provided by our framework can expedite the development of compression OCE.

Spatial resolution in dynamic optical coherence elastography

“…It is interesting that, although Qian et al 29 reached similar conclusions and correctly defined resolution in conventional US elastography, they incorrectly reported that the effective lateral resolution in dynamic OCE is defined by the capabilities of the OCT imaging system. As shown in this work (as well as by Hepburn et al 17 ), the resolution in both wave-based and compression OCE is not defined solely by the detection mechanism of OCT.…”

“…This definition was recently applied in the field of compression OCE. 17 Using this approach, the propagating elastic wave used to infer modulus in dynamic OCE is typically assumed to behave as a step function at a material interface perpendicular to the propagation direction. Thus, the spatial resolution in dynamic OCE is usually defined by the lateral (perpendicular to light propagation direction) resolution of the optical measurement system.…”

“…In dynamic OCE, the typical assumption of an infinite, homogeneous, nearly incompressible elastic material would suggest that the elastographic resolution can be described by the OCT image resolution alone, yet, spatial resolution has been reported to range from the micron scale to multiple millimeters for similar reconstruction methods based on elastic wave propagation. [20][21][22][23][24][25][26][27][28] Recently, it was suggested that the mechanical model of the medium is directly related to resolution in the closely related field of compression OCE, 17 thus indicating that spatial resolution is not always defined by the resolution of the imaging method (OCT).…”

“…Similar sigmoid-based fits have been used to describe elastic resolution in other studies. 17,22,29,[52][53][54] 5 Results…”

Handheld probe for quantitative micro-elastography

“…Phase-sensitive detection is used to generate a map of axial displacement between B-scan pairs acquired at each y-location [28]. The axial perturbation strain can be estimated as the gradient of the axial displacement map with depth, over a sliding window of typically 15-100 µm using least-square linear regression [26,29]. The bulk strain at every (x, y) location in the silicone layer is estimated by measuring the thickness of the top section of the layer in the OCT image.…”