Manganese-Enhanced Magnetic Resonance Imaging And Its Applications In Studying Olfactory Functions And Cerebral Ischemia In Rat

Recently, there are growing interests in a new functional magnetic resonance imaging technique namely manganese enhanced magnetic resonance imaging (MEMRI), which can be used for tracing neuronal tracts and studying brain functions in vivo. The purposes of the work presented in this dissertation is to implement and develop the MEMRI technique and use it to trace neuronal tracts in the olfactory system of rat and to study the phenomenon of "calcium overloading" in a rat model of focal cerebral ischemia.Firstly, after choosing the proper imaging sequences and optimizing the concentration of Mn²⁺ applied and the design of the experiments, we used inversion-recovery prepared T₁-weighted imaging sequence to obtain high spatial resolution images of the olfactory bulbs (OB) in rat, in which the laminar structures of the bulbs can be unambiguously identified. The high spatial resolution images of the OB enable us to study the transportation of Mn²⁺ ion among the laminar structures of the OB. The transportation rate of Mn²⁺ among the laminar structures was shown to be approximately 0.2 mm/hour under resting condition.Secondly, we used MEMRI to trace anterogradely neuronal projections from the olfactory epithelium (OE) to the OB in rat. Our results agreed well with what predicted by the well-known "zone-to-zone" and "glomerular convergence" principles. We compared the transportation rates of Mn²⁺ along the olfactory pathway under resting condition and under odor stimulation. It was found that, even in urethane-anesthetized rats, Mn²⁺ moves faster in the olfactory pathway when under odor stimulation.Finally, we used MEMRI to monitor the so-called "calcium overload" in a rat model of focal cerebral ischemia. It was found that the total area of brain regions with Mn²⁺ accumulation was less than the area of the ischemic brain regions shown by diffusion-weighted imaging (DWI). We suggest that MEMRI can provide a new dimension of information in the early detection of ischemic core and in identifying ischemic penumbra.