Magnetic resonance perfusion imaging and double quantum coherence transfer magnetic resonance spectroscopy
The thesis is composed of two parts. Magnetic resonance (MR) perfusion imaging using continuous arterial spin tagging (CAST) and double quantum (DQ) coherence transfer MR spectroscopy (MRS) are the main themes respectively. Part one first discusses the importance of cerebral blood flow (CBF) measurements for both clinical management and experimental investigation of neurological diseases such as ischemic stroke. This is followed by a review of the commonly used methods for measuring CBF. MR perfusion imaging using CAST is then discussed, starting with derivation of a general equation for CBF calculation. A comprehensive examination of all the factors affecting absolute CBF quantification and an error propagation analysis to estimate the signal-to-noise ratio of the perfusion images (SNRperfu) obtained with this technique are then given. A strategy to optimize SNRperfu in one-coil CAST perfusion imaging is proposed and demonstrated experimentally. Improved SNRperfu enables higher temporal resolution for perfusion measurements, as is demonstrated experimentally with an acetazolamide stimulation test. With the MR perfusion imaging technique developed, the effects of anesthetics on CBF in rats were investigated. CBF in rats after transient focal cerebral ischemia was also measured. A delayed hyperemia in brain regions sustaining ischemic injuries was observed. DQ coherence transfer or DQ filtering (DQF) is a common spectral editing technique used in 'in vivo' proton MRS to suppress water/lipid signals and to eliminate spectral overlapping. Part two of the thesis involves developing new DQF techniques and improving existing DQF techniques with the objective of making them more useful for practical applications. A localized DQF sequence for 'in vivo' observation of taurine was developed and optimized. This may be useful as a tool in investigating the pathophysiology of taurine-related disorders. Because the conventional DQF sequences recover spectra of only one metabolite at a time, a stimulated-echo enhanced selective DQ coherence transfer sequence and a DQ double-editing sequence were developed, both of which are capable of observing more than one metabolite simultaneously. Finally, spatial localization using two-dimensional longitudinal Hadamard encoding was combined with a conventional DQF sequence to acquire multiple-voxel localized and lactate edited spectra 'in vivo'.