Magnetic resonance imaging
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Comparative Study
Anatomical and functional MR imaging in the macaque monkey using a vertical large-bore 7 Tesla setup.
Functional magnetic resonance imaging (MRI) in the nonhuman primate promises to provide a much desired link between brain research in humans and the large body of systems neuroscience work in animals. We present here a novel high field, large-bore, vertical MR system (7 T/60 cm, 300 MHz), which was optimized for neuroscientific research in macaque monkeys. A strong magnetic field was applied to increase sensitivity and spatial resolution for both MRI and spectroscopy. ⋯ On functional activation we observed flow increases of up to 38% (59 to 81 ml/100 g/min) in the primary visual cortex, V1. Compared to BOLD maps, functional CBF maps were found to be localized entirely within the gray matter, providing unequivocal evidence for high spatial specificity. The exquisite sensitivity of the system and the increased specificity of the hemodynamic signals promise further insights into the relationship of the latter to the underlying physiological activity.
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Localized cerebral in vivo 1H NMR spectroscopy (MRS) was performed in the anesthetized as well as the awake monkey using a novel vertical 7 T/60 cm MR system. The increased sensitivity and spectral dispersion gained at high field enabled the quantification of up to 16 metabolites in 0.1- to 1-ml volumes. Quantification was accomplished by using simulations of 18 metabolite spectra and a macromolecule (MM) background spectrum consisting of 12 components. ⋯ Periods with major motion artifacts were rejected, while a frequency/phase correction was performed on the remaining single spectra before averaging. In resting periods, both spectral amplitude and line width, that is, the voxel shim, were unaffected permitting reliable measurements. The corrected spectra obtained from the awake monkey afforded the reliable detection of 6-10 cerebral metabolites of 1-ml volumes.