Search

Purpose: The aim of the current study was to compare the reproducibility of sodium (23Na)‐T1 estimation using a centric‐reordered saturation recovery (SR) true fast imaging with steady‐state precession (TrueFISP) and a variable flip angle (VFA) spoiled gradient echo (GRE). Additionally, we evaluated the effect of spatial averaging on 23Na‐T1 estimation by the two methods. Methods: Measurements were performed in the phantom, consisting of 10 dm3 volume rectangular polyethylene container filled with distilled water solution of 0.6% NaCl + 0.004% CuSO4, using a dual‐tunable 23Na/1H coil at 3 Tesla. 23Na images were acquired for FOV = 384 × 384 mm2 and voxel size = 6 × 6 × 6 mm3 using: (1) TrueFISP: TR/TE = 900/1.5 ms, flip angle = 90°, bandwidth = 450 Hz/px, and (2) GRE: TR/TE = 30/1.5 ms, bandwidth = 350 Hz/px. 23Na‐T1 weightings were obtained with nonselective saturation prepulses delayed from the center of the k‐space acquisition by 25/40/60/130/280 ms (SR‐TrueFISP) and by applying different nominal flip angles: 10°/30°/50°/70°/90° (VFA‐GRE). Both sequences were acquired twice, applying 20 and 30 spatial averages. The resulting images were B1‐corrected with a double‐angle GRE method. Results: Image acquisition varied from 5:41 to 9:37 for TrueFISP and from 12:48 to 19:12 min for GRE using 20 and 30 spatial averages, respectively. Higher averaging increased the acquisition time by 53% and mean SNR at scan < 10%, without an effect on 23Na‐T1 estimations with both methods (SR‐Truefisp |Δ| = 1.58 ms, VFA‐GRE |Δ| = 0.53 ms; for SNR P <.001). Overall, mean ± SD of 23Na‐T1 was found as 51 ± 3 ms with SR‐TrueFISP and 53 ± 2 ms with VFA‐GRE. Conclusion: Both SR‐TrueFISP and VFA‐GRE provided similar 23Na‐T1 estimates based on the phantom measurements with isotropic resolution. [ABSTRACT FROM AUTHOR]

We here revisited the concept that glymphatic clearance is enhanced by sleep and anesthesia. Utilizing dynamic magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and fluorescent fiber photometry, we report brain glymphatic clearance is enhanced by both sleep and anesthesia, and sharply suppressed by wakefulness. Another key finding was that less tracer enters the brains of awake animals and that brain clearance across different brain states can only be compared after adjusting for the injected tracer dose.