Abstract
There are a variety of approaches used to create elastography images. Techniques based on shear wave propagation have received significant attention. However, there remain some limitations and problems due to shear wave reflections, limited penetration in highly viscous media, requirements for prior knowledge of wave propagation direction, and complicated propagation in layers where surface acoustic waves and guided waves are dominant. To overcome these issues, reverberant shear wave elastography (RSWE) was proposed as an alternative method which applies the concept of a narrow-band diffuse field of shear waves within the tissue. Since 2017, the RSWE approach has been implemented in ultrasound (US) and optical coherence tomography (OCT). Specifically, this approach has been implemented in these imaging modalities because they are similar in image formation principles and both share several approaches to estimate the biomechanical properties in tissues. Moreover, they cover different spatial-scale and penetration depth characteristics. RSWE has shown promising results in the elastic and viscoelastic characterization of multiple tissues including liver, cornea, and breast. This review summarizes the 4-year progress of the RSWE method in US and OCT. Theoretical derivations, numerical simulations, and applications inex vivoandin vivotissues are shown. Finally, we emphasize the current challenges of RSWE in terms of excitation methods and estimation of biomechanical parameters for tissue-specific cases and discuss future pathways for thein vivoandin situclinical implementations.
Highlights
The biomechanical tissue properties are strongly tied to pathological and physiological states involving alterations of elasticity, viscosity, and structure [1,2,3,4,5]
OCT-reverberant shear wave elastography (RSWE) used a custom built spectral-domain phase-sensitive optical coherence tomography (PhS-OCT) system for the motion detection of waves generated in the sample by a synchronized mechanical excitation system [16]
The application of numerical simulation has demonstrated to be an important tool to validate the mathematical framework of the RSWE approach, the different studies have reported simulations including the superposition of multiple random shear waves
Summary
The biomechanical tissue properties are strongly tied to pathological and physiological states involving alterations of elasticity, viscosity, and structure [1,2,3,4,5]. US-OCT Reverberant Shear Wave Elastography could allow an early detection and treatment of numerous diseases and a better evaluation of the physiological conditions at different levels: cells, tissues, and organs. USE and OCE are similar in their image formation principles and both share several approaches to estimate the biomechanical properties in tissues. They cover different spatial-scale and penetration depth characteristics. Commercial USE can generate elasticity maps with resolution in the millimeter range at a depth penetration of approximately 1–7 cm, enabling the imaging of organ-size tissues. OCE offers spatial mechanical resolution in the micrometer range at a depth penetration of 1–10 mm, enabling the observation of diminutive tissues with higher resolution
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