Decreased water T in fatty infiltrated skeletal muscles of patients with neuromuscular diseases.

Quantitative imaging techniques are emerging in the field of magnetic resonance imaging of neuromuscular diseases (NMD). T of water (T ) is considered an important imaging marker to assess acute and chronic alterations of the muscle fibers, being generally interpreted as an indicator for "disease activity" in the muscle tissue. To validate the accuracy and robustness of quantitative imaging methods, H magnetic resonance spectroscopy (MRS) can be used as a gold standard. The purpose of the present work was to investigate T of remaining muscle tissue in regions of higher proton density fat fraction (PDFF) in 40 patients with defined NMD using multi-TE single-voxel H MRS. Patients underwent MR measurements on a 3 T system to perform a multi-TE single-voxel stimulated echo acquisition method (STEAM) MRS (TE = 11/15/20/25(/35) ms) in regions of healthy, edematous and fatty thigh muscle tissue. Muscle regions for MRS were selected based on T -weighted water and fat images of a two-echo 2D Dixon TSE. MRS results were confined to regions with qualitatively defined remaining muscle tissue without edema and high fat content, based on visual grading of the imaging data. The results showed decreased T values with increasing PDFF with R  = 0.45 (p < 10 ) (linear fit) and with R  = 0.51 (exponential fit). The observed dependence of T on PDFF should be considered when using T as a marker in NMD imaging and when performing single-voxel MRS for T in regions enclosing edematous, nonedematous and fatty infiltrated muscle tissue.