DT-MRI Based Computation of Collagen Fiber Deformation in Human Articular Cartilage: A Feasibility Study

Abstract

Accurate techniques for simulating the deformation of soft biological tissues are an increasingly valuable tool in many areas of biomechanical analysis and medical image computing. To model the complex morphology and response of articular cartilage, a hyperviscoelastic (dispersed) fiber-reinforced constitutive model is employed to complete two specimen-specific finite element (FE) simulations of an indentation experiment, with and without considering fiber dispersion. Ultra-high field Diffusion Tensor Magnetic Resonance Imaging (17.6 T DT-MRI) is performed on a specimen of human articular cartilage before and after indentation to approximately 20% compression. Based on this DT-MRI data, we detail a novel FE approach to determine the geometry (edge detection from first eigenvalue), the meshing (semi-automated smoothing of DTI measurement voxels), and the fiber structural input (estimated principal fiber direction and dispersion). The global and fiber fabric deformations of both the un-dispersed and dispersed fiber models provide a satisfactory match to that estimated experimentally. In both simulations, the fiber fabric in the superficial and middle zones becomes more aligned with the articular surface, although the dispersed model appears more consistent with the literature. In the future, a multi-disciplinary combination of DT-MRI and numerical simulation will allow the functional state of articular cartilage to be determined in vivo.

Computational investigation of in situ chondrocyte deformation and actin cytoskeleton remodelling under physiological loading

“…A transversely isotropic model for cartilage, surrounding a passive non-contractile isotropic elastic chondrocyte, has been employed to analyse cell deformation during compression [17]. A viscoelastic fibre-reinforced constitutive model based on a convex strain-energy function has been used to model collagen fibre and cartilage deformation during indentation, without explicitly modelling chondrocytes embedded in the tissue [33,87]. The current study, for the first time, includes cells with a phenomenological collagen fibre model which is based on the Holzapfel-Gasser-Ogden strain energy potential to simulate both chondrocyte and cartilage tissue deformation.…”

On Fiber Dispersion Models: Exclusion of Compressed Fibers and Spurious Model Comparisons

“…In recent years continuum mechanical models of this response for tissues such as arteries, the myocardium, heart valves, corneas and articular cartilage have been developed to accommodate the effect of collagen fiber dispersion embedded within a noncollagenous matrix material. There are now many imaging modalities available that can identify fiber orientations within tissues; in particular, second-harmonic generation, see, e.g., [1], and ultra-high field diffusion tensor magnetic resonance imaging, see, e.g., [2]. These modalities are able to capture the 3D distribution of collagen fiber orientations without damage to the tissue, in contrast to histological investigations.…”

Monitoring Tissue Engineering and Regeneration by Magnetic Resonance Imaging and Spectroscopy

“…The molecular dynamics is an indirect measure of tissue viscosity which is an important indicator of tissue functionality [33,34]; 5) Specific MRI technqiues that provide direct quantitative measure of tissue growth [35][36][37] include: sodium MRI and the T1 rho MRI for quantifying the proteoglycan (GAG) molecules associated with proteoglycans, diffusion tensor imaging (DTI) for observing collagen fibril direction, and SWIFT MRI for visualizating soft tissue components.…”