Transverse Isotropic Multiscale Muscle Phantom for MR Elastography

2017-11-01T00:00:00Z (GMT) by Martina Guidetti
Magnetic Resonance Elastography (MRE) is a noninvasive imaging technique employed to assess biological tissues properties (shear stiffness) by inducing mechanical wave propagation in the region of interest. For skeletal muscles, an abnormal stiffness indicates various diseases like spasticity, Duchenne muscular dystrophy and hyperthyroidism. Thus, muscle mechanical properties characterization becomes fundamental to a better understanding of the mechanisms accountable for muscle adaptation and the function of muscle, potentially allowing one to follow treatment effects in time. The challenge in employing MRE on muscular tissue is to characterize a non-homogeneous, viscoelastic, and anisotropic material through an inversion algorithm based on the underlying equations of wave motion, so as to obtain distribution of the shear stiffness of the material from the map of its displacement fields. The chosen approach to improve MRE data acquisition protocols is to develop phantoms that realistically simulate properties of soft tissues. This work deals with the optimization of the mechanical and geometrical properties of a phantom that has to show both viscoelastic and anisotropic characteristics similar to those of skeletal muscle when subject to a MRE experiment. A phantom with known and controllable anisotropic viscoelastic properties similar to striated skeletal muscle is developed using a polyvinyl alcohol (PVA) solution 10% w/v in which are positioned four fibers made of Spandex. Then this phantom is immersed in gelatin solution 10% w/v and put in a test tube for MRE multi-frequency experiments. A finite element (FE) model of the same phantom is realized in Solidworks and imported into Comsol Multiphysics in order to simulate a virtual MRE experiment and then compare the experimental results with the computational ones. Once the FE model has been validated, it can be used to rapidly simulate more complex structures that are closer in design to striated muscle. The simulations can elucidate the relationship between the multiscale geometric features of muscle and its relevant macroscopic viscoelastic and anisotropic properties as detected through the MRE technique.