Abstract
A numerical framework for interstitial fluid pressure imaging (IFPI) in biphasic materials is investigated based on three-dimensional nonlinear finite element poroelastic inversion. The objective is to reconstruct the time-harmonic pore-pressure field from tissue excitation in addition to the elastic parameters commonly associated with magnetic resonance elastography (MRE). The unknown pressure boundary conditions (PBCs) are estimated using the available full-volume displacement data from MRE. A subzone-based nonlinear inversion (NLI) technique is then used to update mechanical and hydrodynamical properties, given the appropriate subzone PBCs, by solving a pressure forward problem (PFP). The algorithm was evaluated on a single-inclusion phantom in which the elastic property and hydraulic conductivity images were recovered. Pressure field and material property estimates had spatial distributions reflecting their true counterparts in the phantom geometry with RMS errors around 20% for cases with 5% noise, but degraded significantly in both spatial distribution and property values for noise levels > 10%. When both shear moduli and hydraulic conductivity were estimated along with the pressure field, property value error rates were as high as 58%, 85% and 32% for the three quantities, respectively, and their spatial distributions were more distorted. Opportunities for improving the algorithm are discussed.
Highlights
Magnetic resonance elastography (MRE) is a noninvasive, quantitative imaging technique that characterizes material property distributions of biological tissues through application of appropriate constitutive models
The new interstitial fluid pressure imaging (IFPI) approach eliminates the need for type I (Dirichlet) boundary conditions on the pressure field in favor of estimating type II (Neumann) pressure boundary conditions through the governing poroelastic equations by applying the differential operators to the measured mechanical motion
pressure boundary conditions (PBCs) for the forward problem are defined as Neumann type and estimated based entirely from the full volume displacement data available from MRE
Summary
Magnetic resonance elastography (MRE) is a noninvasive, quantitative imaging technique that characterizes material property distributions of biological tissues through application of appropriate constitutive models. Previous work has generally modeled biological tissue as a single solid matrix that is linearly elastic, isotropic, and nearly incompressible, and has focused on estimating the viscoelastic properties of breast [1,2,3], liver [4, 5], muscle [6,7,8], and prostate [9].
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