Structure of the water resonance in small voxels in rat brain detected with high spectral and spatial resolution MRI

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Abstract
Purpose: To acquire high spectral and spatial resolution (HiSS) MR images of the water resonance in rat brain, evaluate the lineshape of the water resonance in small voxels, and compare images derived from HiSS data with conventional images.Materials and Methods: Spectroscopic images of rat brain were obtained at 4.7 Tesla using phase encoding gradients only. Spectral resolution in each voxel was ∼8 Hz and bandwidth was 1000 Hz. Spatial resolution was ∼250 microns in 1‐mm slices. Images were synthesized to show the water signal integral, peak height, linewidth, resonance frequency, and asymmetry.Results: Two or more resolved components of the water resonance were detected in ∼14% ± 6% of voxels in the brains of eight rats. The water resonances in ∼20% ± 10% of voxels (n = 8) were highly asymmetric. Images with intensity proportional to water signal peak height, T2*, or to selected components of the water resonance showed features that were not evident in conventional images.Conclusions: The complexity of the water signal reflects the anatomy and physiology of the sub‐voxelar environment, and may be a useful source of image contrast. HiSS imaging of brain provides accurate anatomic information, and may improve image contrast and delineation of subtle anatomic features. J. Magn. Reson. Imaging 2002;16:547–552.

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