G.P.368 - Accelerated multi spin echo NMR imaging for muscle water T2 and fat fraction determination with compressed sensing

Abstract

Water T2 and fat fractions (FF) are imaging biomarkers of lesional and degenerative processes in muscular disorders. It was recently shown that muscle water T2 and FF can be estimated by fitting a two-component extended phase graph model onto a standard multi-slice multi-echo (MSME) acquisition. In order to decrease scanning time, we propose to accelerate the acquisition by undersampling the k-space and reconstruct the data using a compressed sensing (CS) approach. As a proof of concept, we performed a retrospective 2× undersampling on fully sampled (FS) MSME data acquired at 3T. Experiments were performed on a multi-T2 phantom, with T2 values between 20 and 100 ms and on 15 subjects (5 healthy volunteers, 5 patients with dermatomyositis and 5 patients with fatty infiltrations). Each echo of the MSME sequence was separately reconstructed using a conjugate gradient method with total variation regularization, then EPG was used for parameter estimation. On phantoms, a significant but minimal bias was observed between T2 values determined on FS and CS data (<0.15 ms). On subjects, ROI were manually drawn in 10 muscles of the thighs on each slice of the MSME images. For each group, the reference mean T2 values were respectively 32 (±1.8) ms, 37 (±2.8) ms and 33.5 (±3.2) ms, with FF of 6 (±5)%, 10 (±7)% and 29 (±12)%. The values obtained from CS data were close to identical: 32 (±1.5) ms, 37 (±2.4) ms and 33 (±2.8) ms; 6.4 (±4)%, 10 (±5)% and 30 (±9)%. The 95% limits of agreement were: 0.9 ms, 1 ms, 1.6 ms for T2; and 2.7%, 2.6% and 3.9% for FF. The CS images were visually identical to the FS ones, with no problem to draw the ROIs on CS data. In conclusion, the MSME sequence can be accelerated by a factor of 2 while maintaining high spatial resolution and high precision and accuracy on the estimation of muscle water T2 and FF. This was validated both in vitro and in vivo on healthy volunteers and patients suffering from different neuromuscular disorders.