Optimized motion estimation for MRE data with reduced motion encodes

摘要

Motion estimation is an essential processing step common to all Magnetic Resonance Elastography (MRE) methods. For dynamic techniques, the motion is obtained from a sinusoidal fit of the image phase at multiple, uniformly spaced relative phase offsets, Φ, between the motion and the motion encoding gradients (MEGs). Generally, 4 to 8 uniformly spaced values of Φ are used. We introduce a method, termed RME (reduced motion encodes), of reducing the number of relative phases required, thereby reducing the imaging time for an MRE acquisition. A frequency-domain algorithm was implemented using the Discrete Fourier Transform (DFT) to derive the general least-squares solution for the motion amplitude and phase given an arbitrary number of phase offsets. Simulation result shows that the noise level decreases as the number of Φ increases. The decrease is largest when smaller numbers of Φ are used and becomes less significant as the number increases. The minimum noise is obtained for a specific number, n, of Φ when the phase is evenly distributed with interval π/n. Phantom studies show a similar trend with noise level. The resulting displacement images from different numbers of phase offsets are compared.