Decreased water T₂ in fatty infiltrated skeletal muscles of patients with neuromuscular diseases

Abstract

Quantitative imaging techniques are emerging in the field of magnetic resonance imaging of neuromuscular diseases (NMD). T 2 of water (T 2w ) 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, 1 H magnetic resonance spectroscopy (MRS) can be used as a gold standard.The purpose of the present work was to investigate T 2w of remaining muscle tissue in regions of higher proton density fat fraction (PDFF) in 40 patients with defined NMD using multi-TE single-voxel 1 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 2weighted 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 2w values with increasing PDFF with R 2 = 0.45 (p < 10 −3 ) (linear fit) and with R 2 = 0.51 (exponential fit).The observed dependence of T 2w on PDFF should be considered when using T 2w as a marker in NMD imaging and when performing single-voxel MRS for T 2w in regions enclosing edematous, nonedematous and fatty infiltrated muscle tissue. KEYWORDS fatty infiltration, imaging marker, MRS, NMD, PDFF, quantitative imaging techniques, skeletal muscle, T 2 of water Abbreviations used: ALS, amyotrophic lateral sclerosis; CNM, centronuclear myopathy; DM2, myotonic dystrophy type 2; EPG, extended phase graph; FSHD, facioscapulohumeral muscular dystrophy; GRASE, gradient and spin echo; IBM, inclusion body myositis; LGMD2A, limb girdle muscular dystrophy type 2A; LGMD2I, limb girdle muscular dystrophy type 2I; LGMD2L, limb girdle muscular dystrophy type 2L; MESE, multi-echo spin-echo; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; NMD, neuromuscular diseases; PDFF, proton density fat fraction; STEAM, stimulated echo acquisition method; T2f, T2 of fat; T2w, T2 of water; TSE, turbo spin-echo; VOI, volume of interest

Quantitative MRI of skeletal muscle in a cross‐sectional cohort of patients with spinal muscular atrophy types 2 and 3

“…45 After correction for the increase of T2 caused by fatty infiltration, 46 we found a decrease in T2 that almost exactly follows the simulation of T2 against an increasing fat fraction, similar to a previous study. 26 Therefore, we conclude that a decrease of T2 as we perceived is solely related to partial volume effects caused by the amount of fat infiltration and that the T2 signal increase in itself does not indicate any pathological process. However, if the T2 relaxation of water in fat had a higher value of 30 ms instead of the assumed 20 ms, part of the decreased T2 could potentially be attributed to pathological processes.…”

“…This may be explained by atrophy of muscle fibers. The alternative explanation, in which the decrease of MD reflects changes in viscosity of the extracellular space due to fibrosis 26 is less likely, since it would be accompanied by an invariable FA, as the cellular dimension would not change. Therefore, we hypothesize that our DTI findings indicate ongoing muscular atrophy, fitting the histopathological characteristics of muscle tissue rather than fibrosis.…”

“…A detailed overview of all processing steps and the multicenter reproducibility of the methods can be found in Schlaffke et al 35 Since the T2 and the DTI parameters have a bias with increasing fat contribution, 21,25 simulations were performed to estimate this effect. 21,26 The simulations were performed using multi-compartment extensions of the used models with each compartment simulated as shown in Figure 1.…”

“…16,23,24 The application of qMRI in diseased muscle proposes some technical challenges, as T2 signal and DTI parameters can be influenced or are confounded by fat present in the muscle. 21,25,26 This study aims to document qMRI properties of muscle tissue in SMA. To this end, we explore the feasibility of a scan protocol of the upper leg that includes DIXON, T2 mapping and diffusion tensor imaging (DTI) in a cross-sectional cohort of 31 patients with SMA types 2 and 3, encompassing a broad range of disease severity and disease duration.…”

Quantitative MRI in myositis patients: comparison with healthy volunteers and radiological visual assessment

“…Although most papers, using fat corrected T2 measurements, show increased T2 in myositis. 10,30 Schlaeger et al 31 found that T2 can decrease in neuromuscular disease patients; however, their study sample was heterogeneous including a range of muscular diseases along with myositis.…”