Muscle water T (T ) has been proposed as a biomarker to monitor disease activity and therapy effectiveness in patients with neuromuscular diseases (NMD). Multi-echo spin-echo (MESE) is known to be affected by fatty infiltration. A T -prepared 3D turbo spin echo (TSE) is an alternative method for T mapping, but has been only applied in healthy muscles.To examine the performance of T -prepared 3D TSE in combination with spectral adiabatic inversion recovery (SPAIR) in measuring T in fatty infiltrated muscles based on simulations and in vivo measurements in thigh muscles of patients with NMD.Prospective.One healthy volunteer, 34 NMD patients.T -prepared stimulated echo acquisition mode (STEAM) magnetic resonance spectroscopy (MRS), SPAIR STEAM MRS, and SPAIR T -prepared STEAM MRS were performed in the subcutaneous fat of a healthy volunteer's thigh. T mapping based on SPAIR 2D MESE and SPAIR T -prepared 3D TSE was performed in the NMD patients' thigh region. Multi-TE STEAM MRS was performed for measuring a reference T at different thigh locations.The behavior of the fat spectrum in the SPAIR T -prepared 3D TSE was simulated using Bloch simulations. The in vivo T results of the imaging methods were compared to the in vivo T MRS results.Pearson correlation coefficient with slope and intercept, relative error.The simulated T for the SPAIR T -prepared 3D TSE sequence remained constant within a relative error of not more than 4% up to a fat fraction of 80%. In vivo T values of SPAIR T -prepared 3D TSE were in good agreement with the T values of STEAM MRS (R = 0.86; slope = 1.12; intercept = -1.41 ms). In vivo T values of SPAIR 2D MESE showed large deviations from the T values of STEAM MRS (R = 0.14; slope = 0.32; intercept = 38.83 ms).The proposed SPAIR T -prepared 3D TSE shows reduced sensitivity to fatty infiltration for T mapping in the thigh muscles of NMD patients.1 TECHNICAL EFFICACY: Stage 1.