23 Na-T1 quantification with saturation recovery TrueFISP and variable flip angle GRE at 3T: A phantom study.

Abstract

The aim of the current study was to compare the reproducibility of sodium (23 Na)-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 23 Na-T1 estimation by the two 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 23 Na/1 H coil at 3 Tesla. 23 Na images were acquired for FOV=384×384mm2 and voxel size=6×6×6mm3 using: (1) TrueFISP: TR/TE=900/1.5ms, flip angle=90°, bandwidth=450Hz/px, and (2) GRE: TR/TE=30/1.5ms, bandwidth=350Hz/px. 23 Na-T1 weightings were obtained with nonselective saturation prepulses delayed from the center of the k-space acquisition by 25/40/60/130/280ms (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. Image acquisition varied from 5:41 to 9:37 for TrueFISP and from 12:48 to 19:12min 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 23 Na-T1 estimations with both methods (SR-Truefisp |Δ|=1.58ms, VFA-GRE |Δ|=0.53ms; for SNR P<.001). Overall, mean±SD of 23 Na-T1 was found as 51±3ms with SR-TrueFISP and 53±2ms with VFA-GRE. Both SR-TrueFISP and VFA-GRE provided similar 23 Na-T1 estimates based on the phantom measurements with isotropic resolution.