Simulation and analysis of magnetic resonance elastography wave images using coupled harmonic oscillators and Gaussian local frequency estimation

New methods for simulating and analyzing Magnetic Resonance Elastography (M RE) images are introduced. To simulate a two-dimensional shear wave pattern , the wave equation is solved for a field of coupled harmonic oscillators w ith spatially varying coupling and damping coefficients in the presence of an external force. The spatial distribution of the coupling and the damping constants are derived from an MR image of the investigated object. To vali date the simulation as well as to derive the elasticity modules from experi mental MRE images, the wave patterns are analyzed using a Local Frequency E stimation (LFE) algorithm based on Gauss filter functions with variable ban dwidths. The algorithms are tested using an Agar gel phantom with spatially varying elasticity constants. Simulated wave patterns and LFE results show a high a greement with experimental data. Furthermore, brain images with estimated e lasticities for gray and white matter as well as for exemplary tumor tissue are used to simulate experimental MRE data. The calculations show that alr eady small distributions of pathologically changed brain tissue should be d etectable by MRE even within the limit of relatively low shear wave excitat ion frequency around 0.2 kHz. (C) 2001 Elsevier Science Inc. All rights res erved.