Dynamic Elastography of Pre-stressed Material with Multi-Directional Excitation in High Field MRI System

The main object of this thesis is the design and manufacturing of a mechanical setup to drive multi-directionally-polarized shear wave motion for the purpose of dynamic elastography in a tensile pre-stressed anisotropic biological sample in an Ultra-High Field MRI system. The main requirements for this task are the structural stability of the system at high frequencies, the nonmagnetic materials needed for the manufacturing (since the magnetic field applied is in the order of magnitude of 10 Tesla and magnetic materials pose both a danger and will distort the acquired image), and the connectivity between the actuators and the wave generator to monitor and control the excitation. Once the setup is created, the testing is performed and from the results of the same, the imagining and evaluation steps of the iterative design process are repeated.\\ After an initial analysis of the different Elastography techniques, the focus is set to the Magnetic Resonance Imaging one. The main functioning and hardware requirements are explained, and an overview of the current equipment is provided. Afterward, the design of the setup itself is presented in detail with particular attention to the matching between all the components and the materials adopted to manufacture them. Finally, the testing with different experimental methods is conducted, and the results are discussed and compared with the expected theoretical ones. From this comparison, a conclusion on the validity of the experiments is proposed and some future developments are suggested to continue the work most effectively and efficiently.