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Exploiting ultrashort-T(E) (UTE) MRI, T1-weighted positive contrast can be obtained from superparamagnetic iron oxide nanoparticles (SPIONs), which are widely used as a robust T2-weighted, negative contrast agent on conventional MR images. Our study was designed (a) to optimize the dual-contrast MRI method using SPIONs and (b) to validate the feasibility of simultaneously evaluating the vascular morphology, blood volume and transvascular permeability using the dual-contrast effect of SPIONs. All studies were conducted using 3 T MRI. According to numerical simulation, 0.15 mM was the optimal blood SPION concentration for visualizing the positive contrast effect using UTE MRI (T(E) = 0.09 ms), and a flip angle of 40° could provide sufficient SPION-induced enhancement and acceptable measurement noise for UTE MR angiography. A pharmacokinetic study showed that this concentration can be steadily maintained from 30 to 360 min after the injection of 29 mg/kg of SPIONs. An in vivo study using these settings displayed image quality and CNR of SPION-enhanced UTE MR angiography (image quality score 3.5; CNR 146) comparable to those of the conventional, Gd-enhanced method (image quality score 3.8; CNR 148) (p > 0.05). Using dual-contrast MR images obtained from SPION-enhanced UTE and conventional spin- and gradient-echo methods, the transvascular permeability (water exchange index 1.76-1.77), cerebral blood volume (2.58-2.60%) and vessel caliber index (3.06-3.10) could be consistently quantified (coefficient of variation less than 9.6%; Bland-Altman 95% limits of agreement 0.886-1.111) and were similar to the literature values. Therefore, using the optimized setting of combined SPION-based MRI techniques, the vascular morphology, blood volume and transvascular permeability can be comprehensively evaluated during a single session of MR examination.

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.