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This dissertation, Magnetic Resonance Elastography: Neuronal and Muscular Studies, and a Novel Acoustic Shear Wave Generator by Cho-cheong, Chan, 陳楚莊, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of the thesis entitled Magnetic Resonance Elastography: Neuronal and Muscular Studies, and a Novel Acoustic Shear Wave Generator Submitted by Chan Cho Cheong for the degree of Doctor of Philosophy at The University of Hong Kong in Mar 2007 Magnetic resonance elastography (MRE) is capable of quantitatively depicting the mechanical properties of tissues. In the last few years, MRE has been demonstrated for in vivo applications in the human liver, breast, prostate, skeletal muscle and brain. So far, most studies have made use of mechanical excitation at the surface of the tissue. In some applications, however, it may be desirable to apply well-defined shear waves directly to tissues in a targeted region via a minimally invasive device. In this study a novel needle-based shear wave driver for MRE was developed. The results demonstrated that the needle driver provides shear stiffness estimates that correlate well with those obtained using mechanical testing. Comparisons between MRE acquisitions obtained with surface and needle drivers demonstrated similar results, in general. However, the well-defined wave propagation pattern provided by the needle driver in a targeted region can reduce section orientation-related errors in wavelength estimation that occurs with surface drivers in two-dimensional MRE acquisitions. This study demonstrates that the needle driver is an effective option and it offers advantages over surface drivers for obtaining accurate stiffness estimates in targeted regions that are accessible by the needle. Anisotropic properties of human skeletal muscle were evaluated in vivo with an acoustic wave produced by an inserted moving needle using MRE. The experiments showed that the elasticity of muscle is significantly different when measured parallel and perpendicular to the fibers, confirming that skeletal muscle is mechanically anisotropic and indicating the feasibility of measuring this independent tissue characterization parameter. Insertion of acupuncture needle at acupoint GB 35 and an adjacent non- acupoint during MRE scans was performed to investigate the muscle response towards the motion of the needle in human subjects. The results demonstrated that the anisotropic index with needle inserted at acupoint point is significantly higher than at non-acupoint. The mechanical properties of the muscle may be useful parameters to explain the phenomenon of acupuncture. Measuring the viscoelastic properties of the brain may be useful for characterizing brain disease such as Alzheimer's disease (AD). AD afflicts millions of elderly worldwide but there is no objective method for in vivo early detection. The hypothesis is that the accumulation of beta amyloid plaques in the brain of patients with Alzheimer's disease induces changes in elasticity and viscosity. This study represents an attempt to measure the mechanical properties of the brain using a double transgenic APP/PS1 mouse model and MRE with surface driver. MRE and histological imaging were employed. The data indicated that the decrease of neuro- viscoelasticity correlated well with the increase of senile plaque formation in the same localities. It appears that MRE is potentially useful for the diagnosis and treatment effectiveness of AD and mild-cognitive impairment. (An abstract of 445 words) _________________________ Signature DOI: 10

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