G.P.370 - Simultaneous muscle water T2 and fat fraction mapping from NMR transverse relaxometry with stimulated echo compensation

Abstract

Skeletal muscle inflammation/necrosis and fatty infiltrations are strong indicators of disease activity and progression in many neuromuscular disorders. They can be assessed using different NMR methods, most often muscle T2 relaxometry and water/fat separation techniques. These evaluations are usually performed separately with dedicated sequences. Here, we propose to simultaneously quantify the muscle water T2 and fat fraction from a standard multi-slice multi-echo (MSME) acquisition by fitting a two-component, stimulated echo compensated model onto the acquired data. The thighs of twenty four patients with various degrees of fatty infiltration, five patients with diagnosed myositis and five healthy volunteers were acquired with a 3T scanner. First, fat T2 was estimated in the subcutaneous fat with a single-component Extended-Phase-Graph (EPG) model. This value was then fed to a bi-component EPG model to fit the muscle tissue signal and simultaneously quantify water T2, fat fraction and effective B1+. Fat fraction and water T2 values were validated using gold standard approaches (Dixon and localized proton spectroscopy). The EPG formulation was used to compensate for the effects of stimulated echoes in the experimental data. Unlike a "global" T2, derived from a mono-component EPG analysis, the water T2 estimated with the proposed method did not correlate with the fat fraction. The fat fraction derived from the proposed method correlated well with that of the Dixon method. This T2 estimation method was in good agreement with localized proton spectroscopy. In this study, we demonstrated that simultaneous and accurate estimations of muscle water T2 and fat fraction from standard MSME acquisitions could be achieved, even in the presence of large stimulated echo effects. This was successfully tested on healthy volunteers and patients. This novel approach would be highly valuable in multi-center trials to accurately monitor neuromuscular diseases and treatment response.