T 2 relaxation-time mapping in healthy and diseased skeletal muscle using extended phase graph algorithms

• Published in: Magnetic resonance in medicine Vol. 84; no. 5; pp. 2656 - 2670
• Main Authors: Keene, Kevin R, Beenakker, Jan-Willem M, Hooijmans, Melissa T, Naarding, Karin J, Niks, Erik H, Otto, Louise A M, van der Pol, W Ludo, Tannemaat, Martijn R, Kan, Hermien E, Froeling, Martijn
• Format: Journal Article
• Language: English
• Published: United States 01.11.2020
• Subjects: Algorithms; Calibration; Computer Simulation; Magnetic Resonance Imaging; Muscle, Skeletal - diagnostic imaging; Phantoms, Imaging; motor neuron disease; muscular dystrophy; multi-echo spin echo; T2 of water; extended phase graph; transverse relaxometry
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.28290

Multi-echo spin-echo (MSE) transverse relaxometry mapping using multi-component models is used to study disease activity in neuromuscular disease by assessing the T of the myocytic component (T ). Current extended phase graph algorithms are not optimized for fat fractions above 50% and the effects of inaccuracies in the T calibration remain unexplored. Hence, we aimed to improve the performance of extended phase graph fitting methods over a large range of fat fractions, by including the slice-selection flip angle profile, a through-plane chemical-shift displacement correction, and optimized calibration of T . Simulation experiments were used to study the influence of the slice flip-angle profile with chemical-shift and T estimations. Next, in vivo data from four neuromuscular disease cohorts were studied for different T calibration methods and T estimations. Excluding slice flip-angle profiles or chemical-shift displacement resulted in a bias in T up to 10 ms. Furthermore, a wrongly calibrated T caused a bias of up to 4 ms in T . For the in vivo data, one-component calibration led to a lower T compared with a two-component method, and T decreased with increasing fat fractions. In vivo data showed a decline in T for increasing fat fractions, which has important implications for clinical studies, especially in multicenter settings. We recommend using an extended phase graph-based model for fitting T from MSE sequences with two-component T calibration. Moreover, we recommend including the slice flip-angle profile in the model with correction for through-plane chemical-shift displacements.