UBC Theses and Dissertations
Quantitative NMR imaging and its applications in vivo Stewart, Wendy Anne
The problem of quantifying NMR parameters, measured at a field strength of 0.15 Tesla using a whole body Imaging Instrument, and their potential use in vivo, have been investigated. The spin-lattice relaxation times (T₁) of water doped with various concentrations of paramagnetic species were determined using the inversion-recovery method. Intensity was measured directly from images as a function of tau and T₁ obtained from a three parameter exponential fit of the data. The effects of varying imaging conditions on the values of T₁ obtained, were also examined. The results were compared with T₁ values obtained using a two-point computational method which is available on many commercial imaging instruments. This involves taking the ratio of an inversion-recovery image and a spin-echo image, which eliminates the dependence of the images on the equilibrium magnetization and the repeat time. The spin-spin relaxation times (T₂) were determined using the spin-echo method, of water doped with the same concentrations of paramagnetic species used to study T₁. Intensities were again obtained directly from images as a function of 2 tau and T₂ obtained from a two parameter exponential fit of the data. The effects of diffusion on the values of T₂ obtained were also examined. The values were compared with those obtained from a two-point computational method, which takes the ratio of two spin-echo images with different tau-times. The T₁ and T₂ data were also compared with literature values obtained under conventional spectroscopic conditions, with no magnetic field gradients present. The results of these studies, which compare favourably with those in the literature, have shown that it is possible to obtain reproducible values of T₁ in the range 100-600 ms, with acceptable errors (±12%) under variable imaging conditions. Reproducible values of T₂ can be obtained in the range 40-200 ms, which have errors of ±15% or less. Above this range the effects of diffusion become important. Experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis, was induced in a Macaca fascicularis monkey, and the development of the disease was followed using quantitative NMR imaging. This technique has been shown to be a powerful tool in the study of EAE in primates, since the progression of the disease is accompanied by changes in T₁ and T₂. The indications are that these changes will allow discrimination between areas of inflammation and others which contain demyelination.
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