Maximum Likelihood Estimation of Shear Wave Speed in Transient Elastography

Abstract

Ultrasonic transient elastography (TE), enables to assess, under active mechanical constraints, the elasticity of the liver, which correlates with hepatic fibrosis stages. This technique is routinely used in clinical practice to assess noninvasively liver stiffness. The Fibroscan system used in this work generates a shear wave via an impulse stress applied on the surface of the skin and records a temporal series of radio-frequency (RF) lines using a single-element ultrasound probe. A shear wave propagation map (SWPM) is generated as a 2-D map of the displacements along depth and time, derived from the correlations of the sequential 1-D RF lines, assuming that the direction of propagation (DOP) of the shear wave coincides with the ultrasound beam axis (UBA). Under the assumption of pure elastic tissue, elasticity is proportional to the shear wave speed. This paper introduces a novel approach to the processing of the SWPM, deriving the maximum likelihood estimate of the shear wave speed when comparing the observed displacements and the estimates provided by the Green's functions. A simple parametric model is used to interface Green's theoretical values of noisy measures provided by the SWPM, taking into account depth-varying attenuation and time-delay. The proposed method was evaluated on numerical simulations using a finite element method simulator and on physical phantoms. Evaluation on this test database reported very high agreements of shear wave speed measures when DOP and UBA coincide.

Ultrasound Elastography and MR Elastography for Assessing Liver Fibrosis: Part 1, Principles and Techniques

“…A single-element pistonlike ultrasound transducer mounted on a vibrating actuator generates a transient vibration (“punch”) of short duration (< 30 ms) [16] at a frequency of 50 Hz. The mechanical impulse generates a shear wave that propagates symmetrically with respect to the axis of the single-element transducer [2, 16–20]. The displacements induced by the shear wave are tracked using ultrasonic waves emitted and received at very high frequency (6 kHz) by the single-element ultrasound transducer.…”

DDEFL1 correlated with Rho GTPases activity in breast cancer

“…Shear wave elastography (SWE) is a quantitative technique that computes true tissue elasticity by measuring the velocity of shear waves as they propagate in the tissue. Shear wave propagation speed in tissue is directly determined by tissue stiffness [ 28 – 30 ]. The tumor elasticity was evalutated in cases with standard which had previously been reported, was graded by ultrasound from 1–5 according to SWE images [ 31 , 32 ].…”

Fatty Liver Disease: Pathophysiology and Imaging Features

“…• One-dimensional transient elastography (Fibro scan) uses mechanical vibrator which is in built in the probe itself to create dynamic stress at the body surface with frequency of 40 to 50 Hz for less than 30 seconds which leads to formation of shear waves and velocity of generated shear waves is measured using Young's modulus E without Bmode imaging. 82,83 It also provides fat quantification. However, it lacks morphologic imaging.…”