Assessment of shear modulus of tissue using ultrasound radiation force acting on a spherical acoustic inhomogeneity

Abstract

An ultrasound-based method to locally assess the shear modulus of a medium is reported. The proposed approach is based on the application of an impulse acoustic radiation force to an inhomogeneity in the medium and subsequent monitoring of the spatio-temporal response. In our experimental studies, a short pulse produced by a 1.5-MHz highly focused ultrasound transducer was used to initiate the motion of a rigid sphere embedded into an elastic medium. Another 25 MHz focused ultrasound transducer operating in pulse-echo mode was used to track the displacement of the sphere. The experiments were performed in gel phantoms with varying shear modulus to demonstrate the relationship between the displacement of the sphere and shear modulus of the surrounding medium. Because the magnitude of acoustic force applied to sphere depends on the acoustic material properties and, therefore, cannot be used to assess the absolute value of shear modulus, the temporal behavior of the displacement of the sphere was analyzed. The results of this study indicate that there is a strong correlation between the shear modulus of a medium and spatio-temporal characteristics of the motion of the rigid sphere embedded in this medium.

Estimation of mechanical properties of a viscoelastic medium using a laser-induced microbubble interrogated by an acoustic radiation force

“…The estimated value was 0.06 Pa s which was used in all theoretical calculations. The value corresponded to the results of our previous work, which was 0.1 Pa s. 52,53 The elastic properties were found to be almost independent from the shear viscosity in the measured range. Shear viscosity of porcine and human lens was investigated by another group and the values varied from 0:1660:1 to 0.33 Pa s. 59,60 In reconstruction, the Young's modulus was varied by gelatin concentrations.…”

“…The local elastic properties of the surrounding material were estimated from the temporal characteristics of the sphere's motion and were found to be in good agreement with direct measurements. 52,53 In this paper, we extend our research by employing laserinduced microbubbles as targets for acoustic radiation force in order to assess the mechanical properties of tissue-mimicking phantoms. We measured the maximum displacement as well as the time it took to reach that value of a laser-induced microbubble under the acoustic radiation force.…”

Generalized response of a sphere embedded in a viscoelastic medium excited by an ultrasonic radiation force

“…In the FEM simulation a sampling frequency of 100 kHz was used and the simulation results match the analytic results very well, even at the high frequencies, Thus, in the future, we may have to use a higher pulse repetition frequency for the detection transducer operating in pulse-echo mode, such as the 20 kHz pulse repetition frequency used in previously reported studies. 7,8 A weighted algorithm was used for the fitting and the weights were based on the normalized values of the velocity spectrum. This weighting scheme was chosen so that the information that had the most amplitude and energy was used to determine the model parameters rather than data that had lower amplitude and potentially poorer signal-to-noise ratio.…”

“…This theory was later used in a study to find the shear modulus of gelatin phantoms. 8 To date, solutions for the motion of a sphere have been analyzed in the time-and frequency-domains for elastic and viscoelastic media. However, the Kelvin-Voigt model has been used exclusively to characterize the viscoelastic media.…”

Acoustic radiation force-based elasticity imaging methods

“…These approaches are appealing because the motion of the sphere can be modelled using analytical expressions that can be solved to determine the viscoelastic properties of the background material [76][77][78]. Such methods have been proposed for implementation in the eye using laser-induced gas bubbles [79].…”