Cerebral mapping of glutamate using chemical exchange saturation transfer imaging in a rat model of stress‐induced sleep disturbance at 7.0T

Background Glutamate chemical exchange saturation transfer (GluCEST) imaging has been widely used in brain psychiatric disorders. Glutamate signal changes may help to evaluate the sleep‐related disorders, and could be useful in diagnosis. Purpose To evaluate signal changes in the hippocampus and cortex of a rat model of stress‐induced sleep disturbance using GluCEST. Study Type Prospective animal study. Animal Model Fourteen male Sprague–Dawley rats. Field Strength/Sequence 7.0T small bore MRI / fat‐suppressed, turbo‐rapid acquisition with relaxation enhancement (RARE) for CEST, and spin‐echo, point‐resolved proton MR spectroscopy (1H MRS). Assessment Rats were divided into two groups: the stress‐induced sleep‐disturbance group (SSD, n = 7) and the control group (CTRL, n = 7), to evaluate and compare the cerebral glutamate signal changes. GluCEST data were quantified using a conventional magnetization transfer ratio asymmetry in the left‐ and right‐side hippocampus and cortex. The correlation between GluCEST signal and glutamate concentrations, derived from 1H MRS, was evaluated. Statistical Analysis Wilcoxon rank‐sum test between CEST signals and multiparametric MR signals, Wilcoxon signed‐rank test between CEST signals on the left and right hemispheres, and a correlation test between CEST signals and glutamate concentrations derived from 1H MRS. Results Measured GluCEST signals showed significant differences between the two groups (left hippocampus; 4.23 ± 0.27% / 5.27 ± 0.42% [SSD / CTRL, P = 0.002], right hippocampus; 4.50 ± 0.44% / 5.04 ± 0.34% [P = 0.035], left cortex; 2.81 ± 0.38% / 3.56 ± 0.41% [P = 0.004], and right cortex; 2.95 ± 0.47% / 3.82 ± 0.26% [P = 0.003]). GluCEST signals showed positive correlation with glutamate concentrations (R2 = 0.312; P = 0.038). Data Conclusion GluCEST allowed the visualization of cerebral glutamate changes in rats subjected to sleep disturbance, and may yield valuable insights for interpreting alterations in cerebral biochemical information. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:1866–1872.