Abstract
We present a theoretical framework for strain estimation in optical coherence elastography (OCE), based on a statistical analysis of displacement measurements obtained from a mechanically loaded sample. We define strain sensitivity, signal-to-noise ratio and dynamic range, and derive estimates of strain using three methods: finite difference, ordinary least squares and weighted least squares, the latter implemented for the first time in OCE. We compare theoretical predictions with experimental results and demonstrate a ~12 dB improvement in strain sensitivity using weighted least squares compared to finite difference strain estimation and a ~4 dB improvement over ordinary least squares strain estimation. We present strain images (i.e., elastograms) of tissue-mimicking phantoms and excised porcine airway, demonstrating in each case clear contrast based on the sample’s elasticity.
Highlights
Disease often causes alteration of the elastic properties of tissue [1,2]
A strain estimation method based on weighted least squares (WLS) has been proposed in ultrasound elastography [27], we report its first use in optical coherence elastography (OCE)
The measured parameters were calculated from experimental data for finite difference (FD), ordinary least squares (OLS), WLS and Gaussian smoothed weighted least squares (GS-WLS, black dots) strain estimation methods
Summary
The emerging technique of optical coherence elastography (OCE) is aimed at differentiating tissues by imaging their microscopic elastic properties [3,4,5,6]. In OCE, a tissue sample is subjected to a load (stress) and the resulting local displacement is measured using optical coherence tomography (OCT) [7]. The spatial derivative of the displacement is the strain [1,2], which is indicative of the sample’s elastic properties. The strain is displayed in a two- or threedimensional image, known as an elastogram [2]. The limits on resolution and penetration depth of displacement measurements in OCE are set by OCT, the underlying imaging modality and, lie in the range 1-20 μm and 1-3 mm, respectively
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