Using human body shear wave noise for passive elastography

Abstract

An elastography imaging technique based on passive measurement of shear wave ambient noise generated in the human body (e.g., due to the heart, muscles twitches, and blood flow system) has been developed. This technique merges two recent research developments in medical imaging and physics: (1) recent work on the efficacy of elastographic imaging demonstrating that shear waves are excellent candidates to image tissue elasticity in the human body and (2) theory and experimental verification in ultrasonics, underwater acoustics, and seismology of the concept of extracting coherent Green’s function from random noise cross correlations. These results provide a means for coherent passive imaging using only the human body noise field, without the use of external active sources. Coherent arrivals of the cross correlations of recordings of human body noise in the frequency band 2–50 Hz using skin-mounted accelerometers allows us to estimate the local shear velocity of the tissues. The coherent arrivals emerge from a correlation process that accumulates contributions over time from noise sources whose propagation paths pass through both sensors. The application of this passive elastography technique for constructing biomechanical models of in vivo muscles’ properties will be discussed.