Evaluating Fat-Fraction Accuracy with Hybrid MRI Reconstruction

To demonstrate that the hybrid reconstruction improves the accuracy of the fat-fraction measurements, comparison of MRI measured fat-fraction with MR spectroscopy measured fat-fraction was made in 58 studies (55 patients with 3 patients scanned twice) at 1.5 T that do not include the in vivo scans mentioned earlier. All studies were performed with Institutional Review Board approval and informed written consent. As a reference standard, single voxel magnetic resonance spectroscopy (MRS) using stimulated echo acquisition mode was performed (26 (link)). Imaging parameters of MRI include: 256 × 128 × 24 matrix size, field of view = 35 × 35 cm, 6 echoes, TE₁ = 1.3 ms, ΔTE = 2.0 ms, 5 degree flip angle, and 21-second breath-hold with parallel imaging acceleration. Imaging parameters of MRS included: voxel size = 20 × 20 × 25 mm³, pulse repetition time = 3.5 s to minimize T₁ weighting, 2048 readout points, 1 signal average, receiver bandwidth = ±5 kHz, and 5 echo times at 10, 20, 30, 40, 50 ms (to facilitate T₂ correction), requiring a 21 s breath-hold. The MRS voxel was placed in the right hepatic lobe avoiding large blood vessels and other non-liver tissues. All MRS data were postprocessed by an MR physicist blinded to the MRI results, using AMARES algorithm (27 (link)) in jMRUI (28 (link)). The comparison between MRS and imaging results using the hybrid reconstruction will also be included in a separate clinical study (29 ) based on an earlier report (30 ). In this work, we retrospectively reconstructed the imaging data of all patients using the complex-based
${\mathit{\text{T}}}_2^{\ast }$ -IDEAL as well as the hybrid method. Fat-fraction measurements were obtained in ROIs drawn in the liver co-localized with the MRS voxel and perfectly co-registered between the two reconstructions and were compared with the MR spectroscopy measured fat-fraction.