The water distribution in the pulvinus of Mimosa can be visualized by an NMR imaging technique. After stimulation of a Mimosa plant, water in the lower half of the main pulvinus disappeared, the water previously contained in this area seeming to be transferred to the upper half of the main pulvinus. Movement of the water in conjunction with Mimosa movement was visualized sequentially by a non-invasive NMR imaging procedure.
The purpose of the present study was to clarify the temporal changes of the apparent diffusion coefficients (ADCs) of cerebral metabolites during early focal ischemia using stimulated echo acquisition mode with short echo time at a 7 T magnet to assess the pathophysiology of the reduction in diffusion properties observed both in the ischemic cerebral hemisphere and in the contralateral hemisphere. The ADCs of metabolites in the infarcted hemisphere 1 hour and 3 hours after the onset of ischemia decreased with 25% and 29% for choline containing compounds (Cho), 16% and 26% for creatine and phosphocreatine (Cre), and 19% and 19% for N-acetylaspartate (NAA), respectively, compared with the ADC values 2 hours later in the contralateral hemisphere. There were decreases in the ADC of Cho, Cre, and NAA with 21%, 7%, and 18% 8 hours later, respectively, in the noninfarcted hemisphere, which suggested transhemispheric diaschisis in rats with focal cerebral ischemia. The present study proposed that the diffusion characteristics of the brain metabolites might offer new insights into circulatory and metabolic alteration in the cerebral intracellular circumstance.
A direct postprocessing method for correcting RF inhomogeneity in MR imaging is proposed. First, two images with different flip-angles of theta and 2theta are obtained. Next, the spatial distribution maps of the sensitivity of the surface coil and the B1 field intensity are produced by employing those images. Finally, the correction of the MR image is achieved, dividing the original image by distribution maps of the coil sensitivity and the B1 field intensity. The method was applied to images obtained by a gradient echo sequence and the corrected image is presented.
Conductivity tensor maps of the rat brain were obtained using diffusion magnetic resonance imaging (MRI). Signal attenuations in the cortex and the corpus callosum were measured using the stimulated echo acquisition mode (STEAM) sequence with b factors up to 6000 s/mm(2). Our previously published method was improved to infer 3 x 3 conductivity tensor at the low-frequency limit. The conductivity tensor of the tissue was inferred from the fast component of the diffusion tensor and a fraction of the fast component. The mean conductivity (MC) of the cortex and the corpus callosum was 0.52 and 0.62 S/m, respectively. Diffusion-weighted images were obtained with b factors up to 4500 s/mm(2). Conductivity tensor images were calculated from the fast diffusion tensor images. Tissues with highly anisotropic cellular structures, such as the corpus callosum, the internal capsule, and the trigeminal nerve, exhibited high anisotropy in conductivity. The resulting values corresponded to conductivities at the low-frequency limit because our method assumed electric currents flowing only through extracellular fluid.
Conductivity tensor images of the rat brain were obtained by a method based on diffusion-weighted magnetic resonance imaging (MRI). Diffusion-weighted images were acquired by a 4.7 T MRI system with motion probing gradients (MPGs) applied in three directions. Conductivities in each MPG direction were calculated from the fast component of the apparent diffusion coefficient and the fraction of the fast component, and two-dimensional conductivity tensor was estimated. Regions of interest (ROIs) were selected in the cortex and the corpus callosum. The mean conductivities in each ROI were 0.014 S/m and 0.018 S/m, respectively. The corpus callosum exhibited higher conductivity anisotropy resulting from anisotropic tissue structures such as axons and dendrites.
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