Comparison between shear wave dispersion magneto motive ultrasound and transient elastography for measuring tissue-mimicking phantom viscoelasticity

Abstract

Several methods have been developed over the last several years to analyze the mechanical properties of soft tissue. Elastography, for example, was proposed to evaluate soft tissue stiffness in an attempt to reduce the need for invasive procedures, such as breast biopsies; however, its qualitative nature and the fact that it is operator-dependent have proven to be limitations of the technique. Quantitative shearwave- based techniques have been proposed to obtain information about tissue stiffness independent of the operator. This paper describes shear wave dispersion magnetomotive ultrasound (SDMMUS), a new shear-wave-based method in which a viscoelastic medium labeled with iron oxide nanoparticles is displaced by an external tone burst magnetic field. As in magnetomotive ultrasound (MMUS), SDMMUS uses ultrasound to detect internal mechanical vibrations induced by the interaction between a magnetic field and magnetic nanoparticles. These vibrations generated shear waves that were evaluated to estimate the viscoelastic properties of tissue-mimicking phantoms. These phantoms were manufactured with different concentrations of gelatin and labeled with iron oxide nanoparticles. The elasticity and viscosity obtained with SDMMUS agreed well with the results obtained by traditional ultrasound-based transient elastography.

A magneto-motive ultrasound platform designed for pre-clinical and clinical applications

“…The depth of acquisition (30 mm to 90 mm) of the default used preset here is adequate for most applications, including phantom and pre-clinical studies (Almeida et al, 2015;Colello Bruno et al, 2014). Here, the depth is limited to 30 mm because a minimal propagation path of 10 mm is necessary to estimate the attenuation and velocity of the shear wave by using Equations 2, 3, and 4 (Deffieux et al, 2009).…”

“…In a single-cycle configuration, tracking the ultrasound for a T US = 50 ms is sufficient to analyze MMUS and SDMMUS. Furthermore, the multiple reflections of the shear wave (which occur in the phantom walls) decrease and the overall acquisition time diminishes as compared to harmonic excitation (Almeida et al, 2015).…”

“…Gaussian filter analysis (Parolai, 2009) can be applied to estimate the attenuation coefficient and the phase velocity, to give μ 1 = 5.05 kPa and μ 2 = 2.01 Pa.s at a frequency of 100 Hz. This provides faster and easier frequency dispersion analysis than harmonic excitation (Almeida et al, 2015). However, using magnetic excitation that lasts longer than one cycle facilitates ROE segmentation, which can be improved by applying a relative energy threshold of 30% to 50%.…”

“…Despite the various applications of MMUS, there has been little attention in its implementation in the clinical setting. Successful implementation of MMUS and SDMMUS can provide new opportunities for clinical applications of ultrasound imaging, such as localization of brachytherapy seeds (McAleavey et al, 2003), monitoring of stomach emptying (Bruno et al, 2015), estimation of tissue viscoelasticity (Almeida et al, 2015) and molecular imaging (Evertsson et al, 2014). Moreover, combining photoacoustics with MMUS can also help to improve the sensitivity of the technique to detect multifunctional nanoparticles with multiple contrast mechanisms (Jin et al, 2010;Qu et al, 2011) This study aimed to develop a more practical MMUS platform for application in pre-clinical and clinical trials.…”

Evaluation of magnetic nanoparticle as magneto-motive ultrasound imaging constrast

“…To the best of our knowledge and based on literature review [20][21][22][23], the Kelvin Voigt showed more satisfactory results for viscoelastic materials than the others and it will be use in this thesis for evaluating the viscoelastic parameters. Therefore, we will only discuss the Voigt Model.…”