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This dissertation, Investigation of Microbubbles and MION as Intravascular Susceptibility Contrast Agents in Magnetic Resonance Imaging by Ka-kwun, Kelvin, Wong, 黃嘉冠, 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 Investigation of Microbubbles and MION as Intravascular Susceptibility Contrast Agents in Magnetic Resonance Imaging Submitted by Wong Ka Kwun Kelvin for the degree of Doctor of Philosophy at The University of Hong Kong in Jan 2005 Magnetic resonance imaging (MRI) produces good intrinsic soft-tissue contrast. However, its image contrast is sometimes non-specific or insensitive to pathology. Contrast agent enhances our ability to characterize tissue pathology and physiology and is very valuable in clinical settings. Non-saturated exogenous magnetic susceptibility contrast agents are potentially powerful as their transverse relaxivities has a strong dependence on the magnetic field strength. Novel applications of different intravascular susceptibility contrast agents are demonstrated in this thesis. The potential application of gas microbubbles in MRI as a unique intravascular susceptibility contrast agent was explored. The magnetic susceptibility effect of an ultrasound microbubble contrast agent, Optison(R), was studied and demonstrated with in vivo rat liver imaging at 7 T. Optison(R) suspension in two different doses, 0.15 mL/kg and 0.4 mL/kg, was injected into rats, inducing transverse relaxation rate increases (∆R *) of -1 -1 29.11.6 s (N = 2) and 61.512.9 s (N = 6) respectively in liver tissue. In vivo ∆R * of -1 Optison(R) suspension was measured to be 127.1 s at 7T. This is the first in vivo study of microbubbles as an MR intravascular susceptibility contrast agent. Potential applications include the study of refilling kinetics and the determination of local perfusion level with ultrasound pen in interventional MRI. It might also be possible to monitor the delivery site and dosage in vivo in microbubbles cavitation assisted drug/gene delivery through monitoring contrast changes by dynamic susceptibility imaging. Monocrystalline iron oxide nanoparticle (MION) has a long half-life in plasma and is a strong intravascular susceptibility contrast agent. The relative regional cerebral blood volume (CBV) map was measured based on the change in steady-state transverse relaxation rate (∆R ) at 9.4T. High resolution CBV maps at 100m 100m 600m were reported. Fine details, such as hippocampal fissure, and hippocampus structures CA1, and CA2-CA3 were identified in the CBV map. Potential applications of this technique are to study the vascular factor of dementia and Alzheimer's disease in transgenic mouse models to help us understand the disease. Other potential applications include studying the efficacy of different drugs in preserving vascular functions in transgenic mouse models. This approach was applied to investigate the microvasculature of the mouse heart. The relative regional myocardial blood volume (rMBV) map was measured based on the change in steady-state transverse relaxation rate (∆R *) at 9.4T. The cyclic change of rMBV during the cardiac cycle was obtained. High resolution rMBV at various cardiac points was obtained at 200m 200m 500m resolution. The study showed a general rMBV decrease from end-diastole to end-systole, as expected from a cardiac physiology, and also showed the heterogeneous transmural distribution of rMBV in left ventricular (LV) myocardium. It also showed a higher rMBV in the apex than the mitral valve position

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