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.
Highlights
Optical coherence elastography (OCE) is emerging as a higher resolution alternative to both ultrasound elastography and magnetic resonance elastography in a range of applications including in oncology [1,2,3], cardiology [4,5], ophthalmology [6,7], and dermatology [8,9]
We present a framework for assessing resolution in phase-sensitive compression OCE that combines a model of mechanical deformation using finite-element analysis (FEA) with models of the optical coherence tomography (OCT) system and signal processing based on linear systems theory
These results demonstrate that feature resolution does not match the system resolution, but instead varies significantly within one elastogram
Summary
Optical coherence elastography (OCE) is emerging as a higher resolution alternative to both ultrasound elastography and magnetic resonance elastography in a range of applications including in oncology [1,2,3], cardiology [4,5], ophthalmology [6,7], and dermatology [8,9]. In OCE, the resolution of mechanical properties is intrinsically linked to the mechanical deformation of the sample. OCE elastogram generation can be described in three stages; the deformation of the sample under mechanical loading, the measurement of this deformation using OCT, and the signal processing used to relate measured deformation to elasticity. The goal of elastography is to recover the mechanical properties of the sample by applying mechanical loading and observing the resulting deformation. The change in position of each point in the sample is described by the displacement field, u The sample in both the unloaded and loaded states is taken to be in a state of static equilibrium and, the deformation between the two states is assumed to be much smaller than the size of the sample [30].
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