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Helmholtz Inversion using Unconstrained Optimization for MR Elastography of the Lung: A Comparison to Direct Inversion
Huiming Dong1,2, Rizwan Ahmad2, and Arunark Kolipaka1,2
1Department of Radiology, The Ohio State University Wexner Medical Center, Columbus, OH, United States, 2Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States
A compressed-sensing-based inversion is proposed to estimate lung stiffness. Result demonstrated that the technique yielded more robust stiffness estimates in noisy data compared to direct inversion, and successfully detected higher stiffness at total lung capacity than residual volume.
Figure 1. Flow Diagram. The acquired data are first unwrapped and filtered to obtain displacement u0 for each direction. Subsequently, the cost function is alternatively optimized. λ1 is controlled by a noise feedback loop (in red), allowing denoising for each direction via comparing the variance of uNoise and u-u0. Noise ratio is second harmonic amplitude (SHA)/first harmonic amplitude (FHA) of the non-filtered data.
Table II. Lung Density of All Volunteers.