Magnetic Resonance Elastography in Muscle Tissue based on Anisotropic Assumption

Sammanfattning: Mechanical properties of muscle tissue are linked to its function. Magnetic Resonance Elastography (MRE) has the capability toquantitively measure these mechanical properties of soft tissue in-vivo. However, most MRE methods assume tissue isotropy during MRE reconstruction which is not an appropriate assumption for muscle tissue. To obtain tissue mechanical properties with higher accuracy, muscle anisotropy must be considered during MRE reconstruction. Therefore, the aim of this thesis was to implement an anisotropic MRE reconstruction. The anisotropic MRE reconstruction used solves three independent viscoelastic parameters (G||, G⊥, E||), that is based on a transverse isotropic (TI) inversion. The reconstruction was validated in a phantom study by comparison with an isotropic reconstruction, and in-vivo on gastrocnemius (ankle plantar flexor) and tibialis anterior (ankledorsi flexor) of one human subject. Also, a TI phantom was created to be included in the phantom study along with a commercial isotropic phantom. However, due to poor image quality, the TI phantom was excluded from further validation. Results from the isotropic phantom did not agree with the assumption of equal shear modulus in different planes of the isotropic medium. In-vivo study showed that the anisotropic reconstruction yielded mean moduli values in the range of what the literature suggests. The unequal shear modulus and young's modulus G||≠G⊥≠E|| of anisotropy in TI material was observed, indicating that the reconstruction method was able to identify the anisotropy ofmuscle tissue. However, further analysis including more human subjects are needed to conclude the reliability of the reconstruction method.