Non-invasive assessment of skeletal muscle fibrosis in mice using nuclear magnetic resonance imaging and ultrasound shear wave elastography.

Fibrosis is a key pathological feature in muscle disorders, but its quantification mainly relies on histological and biochemical assays. Muscle fibrosis most frequently is entangled with other pathological processes, as cell membrane lesions, inflammation, necrosis, regeneration, or fatty infiltration, making in vivo assessment difficult. Here, we (1) describe a novel mouse model with variable levels of induced skeletal muscle fibrosis displaying minimal inflammation and no fat infiltration, and (2) report how fibrosis affects non-invasive metrics derived from nuclear magnetic resonance (NMR) and ultrasound shear-wave elastography (SWE) associated with a passive biomechanical assay. Our findings show that collagen fraction correlates with multiple non-invasive metrics. Among them, muscle stiffness as measured by SWE, T2, and extracellular volume (ECV) as measured by NMR have the strongest correlations with histology. We also report that combining metrics in a multi-modality index allowed better discrimination between fibrotic and normal skeletal muscles. This study demonstrates that skeletal muscle fibrosis leads to alterations that can be assessed in vivo with multiple imaging parameters. Furthermore, combining NMR and SWE passive biomechanical assay improves the non-invasive evaluation of skeletal muscle fibrosis and may allow disentangling it from co-occurring pathological alterations in more complex scenarios, such as muscular dystrophies.

Lean regional muscle volume estimates using explanatory bioelectrical models in healthy subjects and patients with muscle wasting.

BACKGROUND: The availability of non-invasive, accessible, and reliable methods for estimating regional skeletal muscle volume is paramount in conditions involving primary and/or secondary muscle wasting. This work aimed at (i) optimizing serial bioelectrical impedance analysis (SBIA ) by computing a conductivity constant based on quantitative magnetic resonance imaging (MRI) data and (ii) investigating the potential of SBIA for estimating lean regional thigh muscle volume in patients with severe muscle disorders. METHODS: Twenty healthy participants with variable body mass index and 20 patients with idiopathic inflammatory myopathies underwent quantitative MRI. Anatomical images and fat fraction maps were acquired in thighs. After manual muscle segmentation, lean thigh muscle volume (lVMRI ) was computed. Subsequently, multifrequency (50 to 350 kHz) serial resistance profiles were acquired between current skin electrodes (i.e. ankle and hand) and voltage electrodes placed on the anterior thigh. In vivo values of the muscle electrical conductivity constant were computed using data from SBIA and MRI gathered in the right thigh of 10 healthy participants. Lean muscle volume (lVBIA ) was derived from SBIA measurements using this newly computed constant. Between-day reproducibility of lVBIA was studied in six healthy participants. RESULTS: Electrical conductivity constant values ranged from 0.82 S/m at 50 kHz to 1.16 S/m at 350 kHz. The absolute percentage difference between lVBIA and lVMRI was greater at frequencies >270 kHz (P < 0.0001). The standard error of measurement and the intra-class correlation coefficient for lVBIA computed from measurements performed at 155 kHz (i.e. frequency with minimal difference) against lVMRI were 6.1% and 0.95 in healthy participants and 9.4% and 0.93 in patients, respectively. Between-day reproducibility of lVBIA was as follows: standard error of measurement = 4.6% (95% confidence interval [3.2, 7.8] %), intra-class correlation coefficient = 0.98 (95% confidence interval [0.95, 0.99]). CONCLUSIONS: These findings demonstrate a strong agreement of lean muscle volume estimated using SBIA against quantitative MRI in humans, including in patients with severe muscle wasting and fatty degeneration. SBIA shows promises for non-invasive, fast, and accessible estimation and follow-up of lean regional skeletal muscle volume for transversal and longitudinal studies.

Quantitative Skeletal Muscle Imaging Using 3D MR Fingerprinting With Water and Fat Separation.

BACKGROUND: Quantitative muscle MRI is a robust tool to monitor intramuscular fatty replacement and disease activity in patients with neuromuscular disorders (NMDs). PURPOSE: To implement a 3D sequence for quantifying simultaneously fat fraction (FF) and water T1 (T1,H2O ) in the skeletal muscle, evaluate regular undersampling in the partition-encoding direction, and compare it to a recently proposed 2D MR fingerprinting sequence with water and fat separation (MRF T1 -FF). STUDY TYPE: Prospective. PHANTOM/SUBJECTS: Seventeen-vial phantom at different FF and T1,H2O , 11 healthy volunteers, and 6 subjects with different NMDs. FIELD STRENGTH/SEQUENCE: 3T/3D MRF T1 -FF, 2D MRF T1 -FF, STEAM MRS ASSESSMENT: FF and T1,H2O measured with the 2D and 3D sequences were compared in the phantom and in vivo at different undersampling factors (US). Data were acquired in healthy subjects before and after plantar dorsiflexions and at rest in patients. STATISTICAL TESTS: Linear correlations, Bland-Altman analysis, two-way repeated measures analysis of variance (ANOVA), Student's t-test. RESULTS: Up to a US factor of 3, the undersampled acquisitions were in good agreement with the fully sampled sequence (R2 ≥ 0.98, T1,H2O bias ≤10 msec, FF bias ≤4 × 10-4 ) both in phantom and in vivo. The 2D and 3D MRF T1 -FF sequences provided comparable T1,H2O and FF values (R2 ≥ 0.95, absolute T1,H2O bias ≤35 msec, and absolute FF bias ≤0.003). The plantar dorsiflexion induced a significant increase of T1,H2O in the tibialis anterior and extensor digitorum (relative increase of +10.8 ± 1.7% and + 7.7 ± 1.4%, respectively, P < 0.05), that was accompanied by a significant reduction of FF in the tibialis anterior (relative decrease of -16.3 ± 4.0%, P < 0.05). Some subjects with NMDs presented increased and heterogeneous T1,H2O and FF values throughout the leg. DATA CONCLUSION: Quantitative 3D T1,H2O and FF maps covering the entire leg were obtained within acquisition times compatible with clinical research (4 minutes 20 seconds) and a 1 × 1 × 5 mm3 spatial resolution. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 2.

Multiexponential Analysis of the Water T2-Relaxation in the Skeletal Muscle Provides Distinct Markers of Disease Activity Between Inflammatory and Dystrophic Myopathies.

BACKGROUND: The monoexponential water T2 (T2-mono ) is a proven biomarker of disease activity in neuromuscular disorders (NMDs). However, it lacks specificity, being elevated in the presence of several pathological processes and pathomorphological alterations in the muscle tissue. PURPOSE: To investigate the multiexponential behavior of the water T2 -relaxation in the skeletal muscle of NMD patients, aiming to identify more sensitive and specific biomarkers of disease activity. STUDY TYPE: Retrospective case-control. POPULATION: Thirty Duchenne muscular dystrophy and 114 inclusion body myositis patients and 55 control subjects. FIELD STRENGTH/SEQUENCE: 3T/Single-voxel proton spectroscopy (1 H-MRS) and multispin-echo (MSE) imaging. ASSESSMENT: Water T2 -decay curves generated from 1 H-MRS data acquired at 14 echo-times were fitted to mono- and biexponential models and the adjusted R2 of each fit was computed. Additionally, T2 spectra were generated from a regularized inverse Laplace transform. For comparison, water T2 maps were generated from the MSE data. The performances of the different variables at identifying patients were assessed via receiver operating characteristic (ROC)-curve analysis. STATISTICAL TESTS: Chi-square, Kruskal-Wallis, and Mann-Whitney with Bonferroni correction for multiple comparisons. RESULTS: T2-mono was elevated in patients (P<0.05), but could not distinguish inclusion body myositis (IBM) from Duchenne muscular dystrophy (DMD). While 79% of IBM data presented a biexponential behavior, this was only 16% and 10% for DMD and control data, respectively (P<0.05). All T2 spectra presented an intermediate-T2 peak characterized by an elevated T2 in patients (P<0.05) and by a relative fraction that was abnormally smaller in IBM patients (P<0.05). Also, a long-T2 peak was exclusively observed in IBM patients. A combination of T2 -spectrum variables performed best at identifying patients. DATA CONCLUSION: T2 spectra not only provided more sensitive and specific markers of disease presence than the T2-mono , but also allowed distinguishing IBM from DMD patients. This must reflect distinct predominant pathological alterations between these diseases, suggesting that these markers provide additional pathophysiological/histopathological information that are missing from T2-mono . LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 3.

Quantitative nuclear magnetic resonance imaging detects subclinical changes over 1 year in skeletal muscle of GNE myopathy.

BACKGROUND AND OBJECTIVE: To identify the most responsive and sensitive clinical outcome measures in GNE myopathy. METHODS: ClinBio-GNE is a natural history study in GNE myopathy. Patients were assessed prospectively by clinical, functional and quantitative nuclear magnetic resonance imaging (qNMRI) evaluations. Strength and functional tests included Myogrip, Myopinch, MoviPlate and Brooke assessments for upper limb and the 6-min walk distance for lower limb. qNMRI was performed for determining the degree of fatty infiltration and trophicity in leg, thigh, forearm and hand skeletal muscles. Ten GNE myopathy patients were included. Three patients were non-ambulant. Age and gender-matched healthy subjects were used as controls. RESULTS: Fatty infiltration and contractile cross-sectional area changed inversely and significantly in lower distal limbs and in proximal lower and distal upper limbs over 1 year. qNMRI indices and functional assessment results were strongly correlated. CONCLUSIONS: Even in a limited number of patients, qNMRI could detect a significant change over a 1-year period in GNE myopathy, which suggests that qNMRI could constitute a surrogate endpoint in this slowly progressive disease. Quantitative NMRI outcome measures can monitor intramuscular fat accumulation with high responsiveness. Longer follow-up should improve our understanding of GNE myopathy evolution and also lead to the identification of non-invasive outcome measures with the highest discriminant power for upcoming clinical trials.

Exploration of New Contrasts, Targets, and MR Imaging and Spectroscopy Techniques for Neuromuscular Disease - A Workshop Report of Working Group 3 of the Biomedicine and Molecular Biosciences COST Action BM1304 MYO-MRI.

Neuromuscular diseases are characterized by progressive muscle degeneration and muscle weakness resulting in functional disabilities. While each of these diseases is individually rare, they are common as a group, and a large majority lacks effective treatment with fully market approved drugs. Magnetic resonance imaging and spectroscopy techniques (MRI and MRS) are showing increasing promise as an outcome measure in clinical trials for these diseases. In 2013, the European Union funded the COST (co-operation in science and technology) action BM1304 called MYO-MRI (www.myo-mri.eu), with the overall aim to advance novel MRI and MRS techniques for both diagnosis and quantitative monitoring of neuromuscular diseases through sharing of expertise and data, joint development of protocols, opportunities for young researchers and creation of an online atlas of muscle MRI and MRS. In this report, the topics that were discussed in the framework of working group 3, which had the objective to: Explore new contrasts, new targets and new imaging techniques for NMD are described. The report is written by the scientists who attended the meetings and presented their data. An overview is given on the different contrasts that MRI can generate and their application, clinical needs and desired readouts, and emerging methods.

Simultaneous muscle water T2 and fat fraction mapping using transverse relaxometry with stimulated echo compensation.

Skeletal muscle inflammation/necrosis and fat infiltration are strong indicators of disease activity and progression in many neuromuscular disorders. They can be assessed by muscle T2 relaxometry and water-fat separation techniques, respectively. In the present work, we exploited differences between water and fat T1 and T2 relaxivities by applying a bi-component extended phase graph (EPG) fitting approach to simultaneously quantify the muscle water T2 and fat fraction from standard multi-slice multi-echo (MSME) acquisitions in the presence of stimulated echoes. Experimental decay curves were adjusted to the theoretical model using either an iterative non-negative least-squares (NNLS) procedure or a pattern recognition approach. Twenty-two patients (age, 49 ± 18 years) were selected to cover a large range of muscle fat infiltration. Four cases of chronic or subchronic juvenile dermatomyositis (age, 8 ± 3 years) were investigated before and 3 months following steroid treatment. For control, five healthy volunteers (age, 25 ± 2 years) were recruited. All subjects underwent the MSME sequence and EPG fitting procedure. The EPG fitting algorithm allowed a precise estimation of water T2 and fat fraction in diseased muscle, even in the presence of large B1(+) inhomogeneities. In the whole cohort of patients, there was no overall correlation between water T2 values obtained with the proposed method and the fat fraction estimated inside muscle tissues (R(2) = 0.02). In the patients with dermatomyositis, there was a significant decrease in water T2 (-4.09 ± 3.7 ms) consequent to steroid treatment. The pattern recognition approach resulted in a 20-fold decrease in processing time relative to the iterative NNLS procedure. The fat fraction derived from the EPG fitting approach correlated well with the fat fraction derived from a standard three-point Dixon method (≈1.5% bias). The bi-component EPG fitting analysis is a precise tool to monitor muscle tissue disease activity and is able to handle bias introduced by fat infiltration and B1(+) inhomogeneities.

New insights on human skeletal muscle tissue compartments revealed by in vivo t2 NMR relaxometry.

The spin-spin (T2) relaxation of (1)H-NMR signals in human skeletal muscle has been previously hypothesized to reveal information about myowater compartmentation. Although experimental support has been provided, no consensus has yet emerged concerning the attribution of specific anatomical compartments to the observed T2 components. Potential application of a noninvasive tool that might offer such information urges the quest for a definitive answer to this question. The purpose of this work was to obtain new information that might help elucidate the mechanism of T2 distribution in muscle. To do so, in vivo T2 relaxation data was acquired from the soleus of eight healthy volunteers using a localized Carr-Purcell-Meiboom-Gill technique. Each acquisition contained 1000 echoes with an interecho spacing of 1 ms. Data were acquired from each subject under different vascular filling preparations expected to change exclusively the extracellular water fraction. Two exponential components were systematically observed: an intermediate component (T2 ~ 32 ms) and a long component (100 < T2 < 210 ms). The relative fraction and T2 value characterizing the long component systematically increased after progressive augmentation of extracellular water volume. Characteristic relaxation behavior for each vascular filling condition was analyzed with a two-site exchange model and a three-site two-exchange model. We show that a two-site exchange model can only predict the observations for small exchange rates, much more representative of transendothelial than transcytolemmal exchange regimes. The three-site two-exchange model representing the intracellular, interstitial, and vascular spaces was capable of precisely predicting the observations for realistic transcytolemmal and transendothelial exchange rates. The estimated intrinsic relative fractions of each of these compartments corroborate with estimations from previous works and strongly suggest that the T2 relaxation from water within the intracellular and interstitial spaces is described by the intermediate component, whereas the long component represents water within the vascular space.