Low Frame Rate Elastometry Using Interference Pattern of Shear Waves

Abstract

Purpose: Elastography is a promising method as a non-invasive test to assess the liver tissue for diagnosing chronic diseases such as fatty liver, fibrosis and cirrhosis. Most of elastography techniques measure the velocity of shear wave propagation in liver to estimate the elasticity. A high frame rate imaging system is usually required to measure the velocity of shear waves which leads to higher complexity and costs.  Inducing interference patterns of shear wave is one of the proposed methods for reducing the frame rate in measuring wave propagation velocity during tissue elastography. Previously, the Nyquist rate must be met in order to provide an appropriate image for extracting the patterns with a reasonable accuracy.
Methods: To reduce the required rate of imaging, static patterns of shear wave interference should be extracted to determine the wavelength and consequently the velocity of shear wave. Shear waves are induced in the tissue using acoustic radiation force. In this article we propose a technique, and apply it to ultrasound images acquired before and after inducing the shear waves to extract the interference pattern. 
Results: The average error in measuring the elasticity of the simulated phantom with the shear wave frequency of 100 Hz is 4.8%.
Conclusion: The method does not impose any restrictions on the time interval between images, so the tissue elasticity can be calculated independent of the imaging rate.