A numerical framework for interstitial fluid pressure imaging in poroelastic MRE

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.

MR elastography: Principles, guidelines, and terminology

“…These effects should be considered if working at very low frequencies or in the lung. Some inversions based on poro‐elastic equations have been reported 101,102 …”

“…Some inversions based on poro-elastic equations have been reported. 101,102 Poro-elastic effects within the lungs are complicated and can affect a wider range of frequencies. Although compression waves travel at about 1500 m/s and 340 m/s in soft tissue and air, respectively, two compression wave speeds may exist simultaneously in a porous material, and they can travel as slowly as 20-30 m/s in lung parenchymal tissue.…”

Separation of fluid and solid shear wave fields and quantification of coupling density by magnetic resonance poroelastography

“…Our motivation is twofold: using spatially resolved maps of the porosity is expected to provide more accurate estimates for the poroelastic parameters than using a global value; and porosity might present itself as a meaningful biomarker to be explored in future studies. While previous applications of poro‐MRE have mainly focused on investigating the compression properties of biological tissues, 9,10 in this work, we will concentrate on shear waves since they provide higher SNR than compression waves. The Biot model for poroelastic wave propagation predicts 1 shear wave mode as opposed to 2 compression wave modes 11 …”

Towards noninvasive estimation of tumour pressure by utilising MR elastography and nonlinear biomechanical models: a simulation and phantom study

“…Alternatively, this velocity can be used as a stand-in for IFP as strong correlation has been shown in some cases 17 and recent work showed it may be a prognostic factor in cervical cancer 18 . An MR elastography method was published that reconstructs images of fluid pressure and hydraulic conductivity distributions in addition to tissue stiffness 19 ; however, results were limited to a single numerical simulation and high errors were reported. Ultrasound elastography techniques have recently been applied to solid stress and tumours, however these have mainly focused on an analysis of the stress or stiffness inside the tumour [20][21][22][23] .…”