Ultrasonic method of microvibration detection: part II - additional processing method and applications

Abstract

Introduction

In the last 28 years, the scientific community has been using elastography to evaluate the mechanical properties of biological tissue. The aim of this work was the optimization of the UDmV method, presented in Part I of the series, by means of modifying the technique employed to generate the reference sine and cosine functions, used for phase-quadrature demodulation, and determining how this modification improved the performance of the method. Additionally, the UDmV was employed to characterize the acoustic and mechanical properties of a 7% gelatin phantom.

Methods

A focused transducer, $T_F$, with a nominal frequency of 2.25 MHz, was used to induce the shear waves, with frequency of 97.644 Hz. Then, the modified UDmV method was used to extract the phase and quadrature components from ultrasonic RF echo-signals collected from four positions along the propagation path of the shear wave, which allowed the investigation of the medium vibration caused by wave propagation. The phase velocity, $c_s$, and attenuation, ${\alpha }_s$, of the phantom were measured and employed in the calculation of shear modulus, μ, and viscosity, η.

Results

The computational simulation demonstrated that the modification in UDmV method resulted in more accurate and precise estimates of the initial phases of the reference sinusoidal functions used for phase-quadrature demodulation. The values for $c_s$ and μ of 1.31 ± 0.01 m·s^-1 and 1.66 ± 0.01 kPa, respectively, are very close to the values found in the literature (1.32 m·s^-1 and 1.61 kPa) for the same material.

Conclusion

The UDmV method allowed estimating of the acoustic and viscoelastic parameters of phantom.

Keywords
Ultrasound; Shear wave; Shear modulus; Viscosity; UDmV; Kalman Filter