Surface wave elastography: device and method

Abstract

Knowledge of the shear elasticity of soft tissues is relevant in many areas of medicine since some diseases correlate with changes in elasticity. Therefore, over the past 30 years, various noninvasive methods have been developed to estimate tissue elasticity. These methods are generally known as elastography. Most of them are ultrasound-based methods requiring specially adapted ultrasound scanners in order to quantify the elasticity. Elastography has the potential to add value and knowledge to other research areas like biomechanics, sports medicine or even the meat and/or agrifood industries. However, the existing solutions are not well adapted to those applications. Hence the need for a portable and reliable elastography method. In this work, we present a nonultrasound surface wave elastography device and method to estimate the shear elasticity of soft tissues. The method is based on surface wave propagation. Inversion algorithms were developed to retrieve the shear elasticity from the surface wave phase velocity in isotropic and transversely isotropic solids. The algorithms take into account near-field effects usually neglected in surface wave elastography. A detailed description of the device is given. The method was tested in tissue-mimicking phantoms and in beef samples. In addition, in vivo applications to estimate the biceps elasticity of two volunteers are shown. The obtained results are comparable to those obtained by other methods, such as shear wave elastography.

Surface wave elastography is a reliable method to correlate muscle elasticity, torque, and electromyography activity level

“…Therefore, the experiments we carried out in this work did not include a direct comparison between the NU‐SWE and another known elastography method. Nevertheless, in previous works, we have performed such comparisons in phantoms and beef samples regarding the ultrasound shear wave elastography (Benech et al, ,2019, 2021; Grinspan et al, 2016). These studies showed that both approaches provide comparable results, especially within the range of frequencies employed in this work.…”

“…If we consider the muscle like a transversely isotropic solid (Gennisson et al, 2005; Nordez & Hug, 2010), the longitudinal shear elastic modulus ( c 55 ) is related to a shear wave propagating in the muscle fibers direction with perpendicular polarization = (where is the muscle mass density = 1000 kg/m 3 ; Benech et al, 2019). Due to the arrangement of the wave source and the linear array of vibration sensors (Figure 1a), the NU‐SWE retrieves .…”

“…Its velocity has a simple relation with the shear elasticity of the tissue. However, this relationship only holds in a semi‐infinite medium and the far‐field of the source (Benech et al, 2019). Since real muscles are finite, and the low‐frequency waves attenuate rapidly in soft tissues (Zhang, 2016), the wave propagation is often measured in the near‐field of the source.…”

“…The complex solutions give rise to a propagating surface wave whose amplitude decays exponentially, termed as the leaky surface wave (Benech et al, 2017). Here, the Rayleigh wave interferes with the leaky wave, having consequences on the phase velocity of the surface field (Benech et al, 2017, 2019). Thus, the exclusive use of low frequencies introduces biases into the estimation of muscle shear elastic modulus.…”

“…The main innovation of such a method lies in the inversion algorithm to calculate the shear wave velocity from the surface displacement field. This algorithm considers the interference between the leaky and Rayleigh waves in the near field of the source and their incidence on the phase velocity (Benech et al, 2017, 2019). This issue is being the object of new developments in the field of elastography (Pitre et al, 2019).…”