Abstract
In the characterization of elastic properties of tissue using dynamic optical coherence elastography, shear/surface waves are propagated and tracked in order to estimate speed and Young’s modulus. However, for dispersive tissues, the displacement pulse is highly damped and distorted during propagation, diminishing the effectiveness of peak tracking approaches, and leading to biased estimates of wave speed. Further, plane wave propagation is sometimes assumed, which contributes to estimation errors. Therefore, we invert a wave propagation model that incorporates propagation, decay, and distortion of pulses in a dispersive media in order to accurately estimate its elastic and viscous components. The model uses a general first-order approximation of dispersion, avoiding the use of any particular rheological model of tissue. Experiments are conducted in elastic and viscoelastic tissue-mimicking phantoms by producing a Gaussian push using acoustic radiation force excitation and measuring the wave propagation using a Fourier domain optical coherence tomography system. Results confirmed the effectiveness of the inversion method in estimating viscoelastic parameters in both the viscoelastic and elastic phantoms when compared to mechanical measurements. Finally, the viscoelastic characterization of a fresh porcine cornea was conducted. Preliminary results validate this approach when compared to other methods.
Highlights
Optical coherence tomography-based elastography (OCE) o®ers the possibility of a noninvasive, high-resolution, and high-contrast measurement of tissue biomechanical properties.[3,4]
By tracking the propagating wave, Young's modulus and other biomechanical parameters can be calculated based on the estimation of the wave speed and the selection of the correct wave propagation model dictated by the boundary conditions of the sample.[11]
Experimental results in elastic and viscoelastic phantoms support the e®ectiveness of the approach when compared to mechanical testing results
Summary
Determining mechanical properties of tissue such as elasticity and viscosity is fundamental for better understanding and diagnosing pathological and physiological processes.[1,2] In this regard, optical coherence tomography-based elastography (OCE) o®ers the possibility of a noninvasive, high-resolution, and high-contrast measurement of tissue biomechanical properties.[3,4] For example, previous studies demonstrate the potential of OCE in assessing mechanical properties of di®erent tissues such as cornea,[5,6] skin,[7] breast,[8] and liver.[9] In particular, a subset of dynamic OCE techniques uses short-duration pulses produced by a selected excitation source in order to produce mechanical wave propagation in the tissue being studied.[10] Excitation sources include acoustic radiation force (ARF), air-pu® excitation, laser-based thermal expansion, and needles connected to piezoelectric vibrators, to name just a few.[11] By tracking the propagating wave, Young's modulus and other biomechanical parameters can be calculated based on the estimation of the wave speed and the selection of the correct wave propagation model dictated by the boundary conditions of the sample.[11]
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