Quantitative MR relaxometry study of muscle composition and function in Duchenne muscular dystrophy

Rotator cuff muscle fibrosis can be assessed using ultrashort echo time magnetization transfer MRI with fat suppression

Muscle degeneration following rotator cuff tendon tearing is characterized by fatty infiltration and fibrosis. While tools exist for the characterization of fat, the ability to noninvasively assess muscle fibrosis is limited. The purpose of this study was to evaluate the capability of quantitative ultrashort echo time T1 (UTE-T1) and UTE magnetization transfer (UTE-MT) mapping with and without fat suppression (FS) for the differentiation of injured and control rotator cuff muscles and for the detection of fibrosis. A rat model of chronic massive rotator cuff tearing (n = 12) was used with tenotomy of the right supraspinatus and infraspinatus tendons and silicone implants to prevent healing. Imaging was performed on a 3-T scanner, and UTE-T1 mapping with and without FS and UTE-MT with and without FS for macromolecular fraction (MMF) mapping was performed. At 20 weeks postinjury, T1 and MMF were measured in the supraspinatus and infraspinatus muscles of the injured and contralateral, internal control sides. Histology was performed and connective tissue fraction (CTF) was measured, defined as the area of collagen-rich extracellular matrix divided by the total muscle area. Paired t-tests and correlation analyses were performed. Significant differences between injured and control sides were found for CTF in the supraspinatus (mean ± SD, 14.5% ± 3.9% vs. 11.3% ± 3.7%, p = 0.01) and infraspinatus (17.0% ± 5.4% vs. 12.5% ± 4.6%, p < 0.01) muscles, as well as for MMF using UTE-MT FS in the supraspinatus (9.7% ± 0.3% vs. 9.5% ± 0.2%, p = 0.04) and infraspinatus (10.9% ± 0.8% vs. 10.1% ± 0.5%, p < 0.01) muscles. No significant differences between sides were evident for T1 without or with FS or for MMF using UTE-MT. Only MMF using UTE-MT FS was significantly correlated with CTF for both supraspinatus (r = 0.46, p = 0.03) and infraspinatus (r = 0.51, p = 0.01) muscles. Fibrosis occurs in rotator cuff muscle degeneration, and the UTE-MT FS technique may be helpful to evaluate the fibrosis component, independent from the fatty infiltration process.

Draft Guidance for Industry Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, and Related Dystrophinopathies - Developing Potential Treatments for the Entire Spectrum of Disease

Background

Duchenne muscular dystrophy (DMD) and related dystrophinopathies are neuromuscular conditions with great unmet medical needs that require the development of effective medical treatments.

Objective

To aid sponsors in clinical development of drugs and therapeutic biological products for treating DMD across the disease spectrum by integrating advancements, patient registries, natural history studies, and more into a comprehensive guidance.

Methods

This guidance emerged from collaboration between the FDA, the Duchenne community, and industry stakeholders. It entailed a structured approach, involving multiple committees and boards. From its inception in 2014, the guidance underwent revisions incorporating insights from gene therapy studies, cardiac function research, and innovative clinical trial designs.

Results

The guidance provides a deeper understanding of DMD and its variants, focusing on patient engagement, diagnostic criteria, natural history, biomarkers, and clinical trials. It underscores patient-focused drug development, the significance of dystrophin as a biomarker, and the pivotal role of magnetic resonance imaging in assessing disease progression. Additionally, the guidance addresses cardiomyopathy's prominence in DMD and the burgeoning field of gene therapy.

Conclusions

The updated guidance offers a comprehensive understanding of DMD, emphasizing patient-centric approaches, innovative trial designs, and the importance of biomarkers. The focus on cardiomyopathy and gene therapy signifies the evolving realm of DMD research. It acts as a crucial roadmap for sponsors, potentially leading to improved treatments for DMD.

Derivation and validation of diagnostic models for myocardial fibrosis in duchenne muscular dystrophy: assessed by multi-parameter cardiovascular magnetic resonance

BACKGROUND

Gadolinium-enhanced cardiovascular magnetic resonance (CMR) is the most widely used approach for diagnosing myocardial fibrosis with late gadolinium enhancement (LGE) in cardiomyopathy associated with Duchenne muscular dystrophy. Given the limitations and safety of gadolinium use, we wanted to develop and evaluate multi-parametric pre-contrast CMR models for the diagnosis of LGE and investigate whether they could be utilised as surrogates for LGE in DMD patients.

METHODS

A total of 136 DMD patients were prospectively recruited and separated into LGE - and LGE + groups. In the first subset of patients (derivation cohort), regression models for the diagnosis of LGE were built by logistic regression using pre-contrast sequence parameters. In a validation cohort of other patients, the models' performances were evaluated.

RESULTS

EF, native T1 and longitudinal strain alone, as well as their combinations form seven models. The model that included EF, native T1 and longitudinal strain had the best diagnostic value, but there was no significant difference in diagnostic accuracy among the other models except EF. In the validation cohort, the diagnosis outcomes of models were moderate consistent with the existence of LGE. The longitudinal strain outperformed the other models in terms of diagnostic value (sensitivity: 83.33%, specificity: 54.55%).

CONCLUSIONS

Pre-contrast sequences have a moderate predictive value for LGE. Thus, pre-contrast parameters may be considered only in a specific subset of DMD patients who cannot cooperate for long-time examinations and have contradiction of contrast agent to help predict the presence of LGE.

TRIAL REGISTRATION NUMBER (TRN)

ChiCTR1800018340 DATE OF REGISTRATION: 20180107.

Robust Assessment of Macromolecular Fraction (MMF) in Muscle with Differing Fat Fraction Using Ultrashort Echo Time (UTE) Magnetization Transfer Modeling with Measured T1

Magnetic resonance imaging (MRI) is widely regarded as the most comprehensive imaging modality to assess skeletal muscle quality and quantity. Magnetization transfer (MT) imaging can be used to estimate the fraction of water and macromolecular proton pools, with the latter including the myofibrillar proteins and collagen, which are related to the muscle quality and its ability to generate force. MT modeling combined with ultrashort echo time (UTE-MT modeling) may improve the evaluation of the myotendinous junction and regions with fibrotic tissues in the skeletal muscles, which possess short T2 values and higher bound-water concentration. The fat present in muscle has always been a source of concern in macromolecular fraction (MMF) calculation. This study aimed to investigate the impact of fat fraction (FF) on the estimated MMF in bovine skeletal muscle phantoms embedded in pure fat. MMF was calculated for several regions of interest (ROIs) with differing FFs using UTE-MT modeling with and without T1 measurement and B1 correction. Calculated MMF using measured T1 showed a robust trend, particularly with a negligible error (<3%) for FF < 20%. Around 5% MMF reduction occurred for FF > 30%. However, MMF estimation using a constant T1 was robust only for regions with FF < 10%. The MTR and T1 values were also robust for only FF < 10%. This study highlights the potential of the UTE-MT modeling with accurate T1 measurement for robust muscle assessment while remaining insensitive to fat infiltration up to moderate levels.

BUDA-MESMERISE: Rapid acquisition and unsupervised parameter estimation for T1 , T2 , M0 , B0 , and B1 maps

PURPOSE

Rapid acquisition scheme and parameter estimation method are proposed to acquire distortion-free spin- and stimulated-echo signals and combine the signals with a physics-driven unsupervised network to estimate T₁ , T₂ , and proton density (M₀ ) parameter maps, along with B₀ and B₁ information from the acquired signals.

THEORY AND METHODS

An imaging sequence with three 90° RF pulses is utilized to acquire spin- and stimulated-echo signals. We utilize blip-up/-down acquisition to eliminate geometric distortion incurred by the effects of B₀ inhomogeneity on rapid EPI acquisitions. For multislice imaging, echo-shifting is applied to utilize dead time between the second and third RF pulses to encode information from additional slice positions. To estimate parameter maps from the spin- and stimulated-echo signals with high fidelity, 2 estimation methods, analytic fitting and a novel unsupervised deep neural network method, are developed.

RESULTS

The proposed acquisition provided distortion-free T₁ , T₂ , relative proton density (M0), B₀ , and B₁ maps with high fidelity both in phantom and in vivo brain experiments. From the rapidly acquired spin- and stimulated-echo signals, analytic fitting and the network-based method were able to estimate T₁ , T₂ , M₀ , B₀ , and B₁ maps with high accuracy. Network estimates demonstrated noise robustness owing to the fact that the convolutional layers take information into account from spatially adjacent voxels.

CONCLUSION

The proposed acquisition/reconstruction technique enabled whole-brain acquisition of coregistered, distortion-free, T₁ , T₂ , M₀ , B₀ , and B₁ maps at 1 × 1 × 5 mm³ resolution in 50 s. The proposed unsupervised neural network provided noise-robust parameter estimates from this rapid acquisition.

Lower extremity MRI following 10-week supervised exercise intervention in patients with diabetic peripheral neuropathy

INTRODUCTION

The purpose of this study was to characterize using MRI the effects of a 10-week supervised exercise program on lower extremity skeletal muscle composition, nerve microarchitecture, and metabolic function in individuals with diabetic peripheral neuropathy (DPN).

RESEARCH DESIGN AND METHODS

Twenty participants with DPN completed a longitudinal trial consisting of a 30-day control period, during which subjects made no change to their lifestyle, followed by a 10-week intervention program that included three supervised aerobic and resistance exercise sessions per week targeting the upper and lower extremities. The participants' midcalves were scanned with multinuclear MRI two times prior to intervention (baseline₁ and baseline₂) and once following intervention to measure relaxation times (T1, T1ρ, and T2), phosphocreatine recovery, fat fraction, and diffusion parameters.

RESULTS

There were no changes between baseline₁ and baseline₂ MRI metrics (p>0.2). Significant changes (p<0.05) between baseline₂ and postintervention MRI metrics were: gastrocnemius medialis (GM) T1 -2.3%±3.0% and soleus T2 -3.2%±3.1%. Trends toward significant changes (0.05<p<0.1) between baseline₂ and postintervention MRI metrics were: calf adipose infiltration -2.6%±6.4%, GM T1ρ -4.1%±7.7%, GM T2 -3.5%±6.4%, and gastrocnemius lateral T2 -4.6±7.4%. Insignificant changes were observed in gastrocnemius phosphocreatine recovery rate constant (p>0.3) and tibial nerve fractional anisotropy (p>0.6) and apparent diffusion coefficient (p>0.4).

CONCLUSIONS

The 10-week supervised exercise intervention program successfully reduced adiposity and altered resting tissue properties in the lower leg in DPN. Gastrocnemius mitochondrial oxidative capacity and tibial nerve microarchitecture changes were not observed, either due to lack of response to therapy or to lack of measurement sensitivity.

Using MRI to quantify skeletal muscle pathology in Duchenne muscular dystrophy: A systematic mapping review

There is a great demand for accurate non‐invasive measures to better define the natural history of disease progression or treatment outcome in Duchenne muscular dystrophy (DMD) and to facilitate the inclusion of a large range of participants in DMD clinical trials. This review aims to investigate which MRI sequences and analysis methods have been used and to identify future needs. Medline, Embase, Scopus, Web of Science, Inspec, and Compendex databases were searched up to 2 November 2019, using keywords “magnetic resonance imaging” and “Duchenne muscular dystrophy.” The review showed the trend of using T1w and T2w MRI images for semi‐qualitative inspection of structural alterations of DMD muscle using a diversity of grading scales, with increasing use of T2map, Dixon, and MR spectroscopy (MRS). High‐field (>3T) MRI dominated the studies with animal models. The quantitative MRI techniques have allowed a more precise estimation of local or generalized disease severity. Longitudinal studies assessing the effect of an intervention have also become more prominent, in both clinical and animal model subjects. Quality assessment of the included longitudinal studies was performed using the Newcastle‐Ottawa Quality Assessment Scale adapted to comprise bias in selection, comparability, exposure, and outcome. Additional large clinical trials are needed to consolidate research using MRI as a biomarker in DMD and to validate findings against established gold standards. This future work should use a multiparametric and quantitative MRI acquisition protocol, assess the repeatability of measurements, and correlate findings to histologic parameters.

Muscle MRI: A biomarker of disease severity in Duchenne muscular dystrophy? A systematic review

OBJECTIVE

To assess the evidence of a relationship between muscle MRI and disease severity in Duchenne muscular dystrophy (DMD).

METHODS

We conducted a systematic review of studies that analyzed correlations between MRI measurements and motor function in patients with DMD. PubMed, Cochrane, Scopus, and Web of Science were searched using relevant keywords and inclusion/exclusion criteria (January 1, 1990-January 31, 2019). We evaluated article quality using the Joanna Briggs Institute scale. Information regarding the samples included, muscles evaluated, MRI protocols and motor function tests used was collected from each article. Correlations between MRI measurements and motor function were reported exhaustively.

RESULTS

Seventeen of 1,629 studies identified were included. Most patients included were ambulant with a mean age of 8.9 years. Most studies evaluated lower limb muscles. Moderate to excellent correlations were found between MRI measurements and motor function. The strongest correlations were found for quantitative MRI measurements such as fat fraction or mean T2. Correlations were stronger for lower leg muscles such as soleus. One longitudinal study reported that changes in soleus mean T2 were highly correlated with changes in motor function.

CONCLUSION

The findings of this systematic review showed that MRI measurements can be used as biomarkers of disease severity in ambulant patients with DMD. Guidelines are proposed to help clinicians choose the most appropriate MRI measurements and muscles to evaluate. Studies exploring upper limb muscles, other stages of the disease, and sensitivity of measurements to change are needed.

Water T2 Mapping in Fatty Infiltrated Thigh Muscles of Patients With Neuromuscular Diseases Using a T2 -Prepared 3D Turbo Spin Echo With SPAIR

BACKGROUND

Muscle water T₂ (T_2w ) 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 T₂ -prepared 3D turbo spin echo (TSE) is an alternative method for T₂ mapping, but has been only applied in healthy muscles.

PURPOSE

To examine the performance of T₂ -prepared 3D TSE in combination with spectral adiabatic inversion recovery (SPAIR) in measuring T_2w in fatty infiltrated muscles based on simulations and in vivo measurements in thigh muscles of patients with NMD.

STUDY TYPE

Prospective.

SUBJECTS

One healthy volunteer, 34 NMD patients.

FIELD STRENGTH/SEQUENCE

T₂ -prepared stimulated echo acquisition mode (STEAM) magnetic resonance spectroscopy (MRS), SPAIR STEAM MRS, and SPAIR T₂ -prepared STEAM MRS were performed in the subcutaneous fat of a healthy volunteer's thigh. T₂ mapping based on SPAIR 2D MESE and SPAIR T₂ -prepared 3D TSE was performed in the NMD patients' thigh region. Multi-TE STEAM MRS was performed for measuring a reference T_2w at different thigh locations.

ASSESSMENT

The behavior of the fat spectrum in the SPAIR T₂ -prepared 3D TSE was simulated using Bloch simulations. The in vivo T₂ results of the imaging methods were compared to the in vivo T_2w MRS results.

STATISTICAL TESTS

Pearson correlation coefficient with slope and intercept, relative error.

RESULTS

The simulated T₂ for the SPAIR T₂ -prepared 3D TSE sequence remained constant within a relative error of not more than 4% up to a fat fraction of 80%. In vivo T₂ values of SPAIR T₂ -prepared 3D TSE were in good agreement with the T_2w values of STEAM MRS (R = 0.86; slope = 1.12; intercept = -1.41 ms). In vivo T₂ values of SPAIR 2D MESE showed large deviations from the T_2w values of STEAM MRS (R = 0.14; slope = 0.32; intercept = 38.83 ms).

DATA CONCLUSION

The proposed SPAIR T₂ -prepared 3D TSE shows reduced sensitivity to fatty infiltration for T_2w mapping in the thigh muscles of NMD patients.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:1727-1736.

An investigation into the effect of body mass index on the agreement between whole-body fat mass determined by MRI and air-displacement plethysmography

OBJECTIVE

To validate MRI fat measurement protocols using purpose built test objects and by comparison with air-displacement plethysmography (ADP) whole-body fat measurements in non-obese subjects.

METHODS

Test objects of known fat concentration were used to quantify the accuracy of the MRI measurements. 10 participants with a body mass index in the range 18-30 underwent whole-body MRI using two different Dixon-based sequences (LAVA Flex and IDEAL IQ) to obtain an estimate of their whole-body fat mass. The MRI determined fat mass was compared to the fat mass determined by ADP.

RESULTS

MRI test object measurements showed a high correlation to expected fat percentage (r > 0.98). The participant MRI and ADP results were highly correlated (r = 0.99) but on average (mean ± standard deviation) MRI determined a higher fat mass than ADP (3.8 ± 3.1 kg for LAVA Flex and 1.9 ± 3.2 kg for IDEAL IQ). There was no trend in the difference between MRI and ADP with total fat mass.

CONCLUSION

The good agreement between MRI and ADP shows that Dixon-based MRI can be used effectively as a tool in physiological research for non-obese adults.

ADVANCES IN KNOWLEDGE

This work found that for ten non-obese subjects body mass index had no effect on the MRI determination of whole-body fat mass.

Quantitative MRI Musculoskeletal Techniques: An Update

OBJECTIVE. For many years, MRI of the musculoskeletal system has relied mostly on conventional sequences with qualitative analysis. More recently, using quantitative MRI applications to complement qualitative imaging has gained increasing interest in the MRI community, providing more detailed physiologic or anatomic information. CONCLUSION. In this article, we review the current state of quantitative MRI, technical and software advances, and the most relevant clinical and research musculoskeletal applications of quantitative MRI.

T2 Mapping and Fat Quantification of Thigh Muscles in Children with Duchenne Muscular Dystrophy

Quantitative magnetic resonance image (MRI) in individual muscles may be useful for monitoring disease progression in Duchenne muscular dystrophy (DMD). The purpose of this study was to measure T2 relaxation time of thigh muscles in children with DMD and healthy boys, and to correlate the T2 relaxation time of muscles with the fat fraction (FF) at quantitative magnetic resonance and results of clinical assessment. Thirty-two boys with DMD and 18 healthy boys were evaluated with T2 mapping and three-point Dixon MRI. Age, body mass index (BMI), muscle strength assessment, timed functional tests (time to walk or run 10 metres, rise from the floor and ascend four stairs), and the North Star Ambulatory Assessment (NSAA) were evaluated. Spearman's correlation was used to assess the relationships between FF and clinical assessments and T2 relaxation time. The mean T2 relaxation time of thigh muscles in DMD was significantly longer than that in the control group (P<0.05), except for the gracilis (P=0.952). The gracilis, sartorius and adductor longus were relatively spared by fatty infiltration in DMD patients. The T2 relaxation time was correlated significantly with the mean FF in all muscles. Age, BMI, total muscle strength score, timed functional tests and NSAA were significantly correlated with the overall mean T2 relaxation time. T2 mapping may prove clinically useful in monitoring muscle changes as a result of the disease process and in predicting the outcome of DMD patients.

Advances in Quantitative Imaging of Genetic and Acquired Myopathies: Clinical Applications and Perspectives

In the last years, magnetic resonance imaging (MRI) has become fundamental for the diagnosis and monitoring of myopathies given its ability to show the severity and distribution of pathology, to identify specific patterns of damage distribution and to properly interpret a number of genetic variants. The advances in MR techniques and post-processing software solutions have greatly expanded the potential to assess pathological changes in muscle diseases, and more specifically of myopathies; a number of features can be studied and quantified, ranging from composition, architecture, mechanical properties, perfusion, and function, leading to what is known as quantitative MRI (qMRI). Such techniques can effectively provide a variety of information beyond what can be seen and assessed by conventional MR imaging; their development and application in clinical practice can play an important role in the diagnostic process and in assessing disease course and treatment response. In this review, we briefly discuss the current role of muscle MRI in diagnosing muscle diseases and describe in detail the potential and perspectives of the application of advanced qMRI techniques in this field.

Non-invasive tracking of disease progression in young dystrophic muscles using multi-parametric MRI at 14T

In this study, multi-parametric magnetic resonance imaging (MRI) was conducted to monitor skeletal muscle changes in dystrophic (mdx^4cv) and age-matched control (C57BL/6J) mice starting at 3 weeks of age. The objective of this study was to evaluate and characterize changes in muscle tissue characteristics of hind limbs in young, dystrophic mice using MRI. Mdx^4cv (n = 25) and age-matched C57BL/6J (n = 5) were imaged at 3, 5, 7, 9, and 11 weeks of age. Multiple MR measurements were taken from the tibialis anterior, gastrocnemius, and soleus muscles. There were significant differences between dystrophic and control groups for all three muscle types when comparing transverse relaxation times (T₂) in lower hind limb muscles. Additionally, fractional anisotropy, radial diffusivity, and eigenvalue analysis of diffusion tensor imaging also demonstrated significant differences between groups. Longitudinal relaxation times (T₁) displayed no significant differences between groups. The earliest time points in the magnetization transfer ratio measurements displayed a significant difference. Histological analysis revealed significant differences in the tibialis anterior and gastrocnemius muscles between groups with the mdx mice displaying greater variability in muscle fiber size in later time points. The multi-parametric MRI approach offers a promising alternative for future development of a noninvasive avenue for tracking both disease progression and treatment response.

Integrative effects of dystrophin loss on metabolic function of the mdx mouse

Duchenne muscular dystrophy (DMD) is a disease marked by the development of skeletal muscle weakness and wasting. DMD results from mutations in the gene for the cytoskeletal protein dystrophin. The loss of dystrophin expression is not limited to muscle weakness but has multiple systemic consequences. Managing the nutritional requirements is an important aspect of the clinical care of DMD patients and is complicated by the poor understanding of the role of dystrophin, and dystrophic processes, in regulating metabolism. Here, we show that mdx mice, a genetic model of DMD, have significantly reduced fat mass relative to wild type C57BL/10. The alteration in body composition is independent of the presence of skeletal muscle disease, as it is still present in mice with transgenic expression of a fully-functional dystrophin in skeletal muscle. Furthermore, mdx mice do not increase their fat mass or body weight when housed under thermoneutral conditions, in marked contrast to C57BL/10 mice. We also demonstrated that mdx mice have significantly reduced fat metabolism and altered glucose uptake. These significant metabolic changes in dystrophic mice implicate dystrophin as an important regulator of metabolism. Understanding the metabolic functions of dystrophin is important for managing the nutritional needs of DMD patients.

Multiparametric quantitative MRI assessment of thigh muscles in limb-girdle muscular dystrophy 2A and 2B

INTRODUCTION

The aim of this study was to apply quantitative MRI (qMRI) to assess structural modifications in thigh muscles of subjects with limb girdle muscular dystrophy (LGMD) 2A and 2B with long disease duration.

METHODS

Eleven LGMD2A, 9 LGMD2B patients and 11 healthy controls underwent a multi-parametric 3T MRI examination of the thigh. The protocol included structural T1-weighted images, DIXON sequences for fat fraction calculation, T2 values quantification and diffusion MRI. Region of interest analysis was performed on 4 different compartments (anterior compartment, posterior compartment, gracilis, sartorius).

RESULTS

Patients showed high levels of fat infiltration as measured by DIXON sequences. Sartorius and anterior compartment were more infiltrated in LGMD2B than LGMD2A patients. T2 values were mildly reduced in both disorders. Correlations between clinical scores and qMRI were found.

CONCLUSIONS

qMRI measures may help to quantify muscular degeneration, but careful interpretation is needed when fat infiltration is massive. Muscle Nerve 58: 550-558, 2018.

Quantifying myofiber integrity using diffusion MRI and random permeable barrier modeling in skeletal muscle growth and Duchenne muscular dystrophy model in mice

PURPOSE

To measure the microstructural changes during skeletal muscle growth and progressive pathologies using the random permeable model with diffusion MRI, and compare findings to conventional imaging modalities such as three-point Dixon and T₂ imaging.

METHODS

In vivo and ex vivo DTI experiments with multiple diffusion times (20-700 ms) were completed on wild-type (n = 22) and muscle-dystrophic mdx mice (n = 8) at various developmental time points. The DTI data were analyzed with the random permeable model framework that provides estimates of the unrestricted diffusion coefficient (D₀ ), membrane surface-to-volume ratio (S/V), and membrane permeability (κ). In addition, the MRI experiments included conventional measures, such as tissue fat fractions and T₂ relaxation.

RESULTS

During normal muscle growth between week 4 and week 13, the in vivo S/V, fractional anisotropy, and fat fraction correlated positively with age (ρ = 0.638, 0.664, and 0.686, respectively), whereas T₂ correlated negatively (ρ = -0.847). In mdx mice, all DTI random permeable model parameters and fat fraction had significant positive correlation with age, whereas fractional anisotropy and T₂ did not have significant correlation with age. Histological measurements of the perimeter-to-area ratio served as a proxy for the model-derived S/V in the cylindrical myofiber geometry, and had a significant correlation with the ex vivo S/V (r = 0.71) as well as the in vivo S/V (r = 0.56).

CONCLUSION

The present study demonstrates that DTI at multiple diffusion times with the random permeable model analysis allows for noninvasively quantifying muscle fiber microstructural changes during both normal muscle growth and disease progression. Future studies can apply our technique to evaluate current and potential treatments to muscle myopathies.

Promethazine Hydrochloride Inhibits Ectopic Fat Cell Formation in Skeletal Muscle

Fatty degeneration of skeletal muscle leads to muscle weakness and loss of function. Preventing fatty degeneration in skeletal muscle is important, but no drug has been used clinically. In this study, we performed drug repositioning using human platelet-derived growth factor receptor α (PDGFRα)-positive mesenchymal progenitors that have been proved to be an origin of ectopic adipocytes in skeletal muscle. We found that promethazine hydrochloride (PH) inhibits adipogenesis in a dose-dependent manner without cell toxicity. PH inhibited expression of adipogenic markers and also suppressed phosphorylation of cAMP response-element binding protein, which was reported to be a primary regulator of adipogenesis. We established a mouse model of tendon rupture with intramuscular fat deposition and confirmed that emerged ectopic adipocytes are derived from PDGFRα⁺ cells using lineage tracing mice. When these injured mice were treated with PH, formation of ectopic adipocytes was suppressed significantly. Our results show that PH inhibits PDGFRα⁺ mesenchymal progenitor-dependent ectopic adipogenesis in skeletal muscle and suggest that treatment with PH can be a promising approach to prevent fatty degeneration of skeletal muscle.

Magnetic Resonance Monitoring of Disease Progression in mdx Mice on Different Genetic Backgrounds

Genetic modifiers alter disease progression in both preclinical models and subjects with Duchenne muscular dystrophy (DMD). Using multiparametric magnetic resonance (MR) techniques, we compared the skeletal and cardiac muscles of two different dystrophic mouse models of DMD, which are on different genetic backgrounds, the C57BL/10ScSn-Dmdmdx (B10-mdx) and D2.B10-Dmdmdx (D2-mdx). The proton transverse relaxation constant (T₂) using both MR imaging and spectroscopy revealed significant age-related differences in dystrophic skeletal and cardiac muscles as compared with their age-matched controls. D2-mdx muscles demonstrated an earlier and accelerated decrease in muscle T₂ compared with age-matched B10-mdx muscles. Diffusion-weighted MR imaging indicated differences in the underlying muscle structure between the mouse strains. The fractional anisotropy, mean diffusion, and radial diffusion of water varied significantly between the two dystrophic strains. Muscle structural differences were confirmed by histological analyses of the gastrocnemius, revealing a decreased muscle fiber size and increased fibrosis in skeletal muscle fibers of D2-mdx mice compared with B10-mdx and control. Cardiac involvement was also detected in D2-mdx myocardium based on both decreased function and myocardial T₂. These data indicate that MR parameters may be used as sensitive biomarkers to detect fibrotic tissue deposition and fiber atrophy in dystrophic strains.

Effects of the Inertia Barbell Training on Lumbar Muscle T2 Relaxation Time

Sun, M-Y, Lu, J-Q, Ma, Z-C, Lü, J-J, Huang, Q, Sun, Y-N, and Liü, Y. Effects of the inertia barbell training on lumbar muscle T2 relaxation time. J Strength Cond Res 34(12): 3454-3462, 2020-The purpose of this study was to investigate variations in T2 relaxation time in normal human lumbar muscles caused by inertia barbell training. Thirty undergraduate healthy men (mean age = 19 ± 1.2 years, body mass = 72 ± 10.0 kg, and height = 1.78 ± 0.1 m) were recruited to participate in this study. Subjects were randomly assigned into 2 groups: an inertia barbell training group (IBTG) (n = 15) and a normal barbell-training group (NBTG) (n = 15). All subjects participated in lumbar flexion and extension muscle strength training for 1 hour per time, 3 times per week for a total of 8 weeks. The lumbar area of each subject was scanned before and after the experiment using a 3.0T superconductive magnetic resonance imaging system. The T2 values measured after intervention were significantly different compared with the T2 values measured before the experiment in both the IBTG and NBTG groups (p < 0.001). After intervention, there was no significant difference in T2 values between the IBTG and NBTG groups (p = 0.17). The ([INCREMENT]T2)/T2 percentage was significantly different in the IBTG group (p < 0.01). This study demonstrated that 8 weeks of strength training led to significant improvements in the values for T2 relaxation time of the lumbar muscles. Furthermore, the ([INCREMENT]T2)/T2 percentage for IBTG was higher than that for NBTG, which suggested that lumbar muscle activity increased more with inertial barbell training.

B1-insensitive T2 mapping of healthy thigh muscles using a T2-prepared 3D TSE sequence

Purpose

To propose a T2-prepared 3D turbo spin echo (T2prep 3D TSE) sequence for B1-insensitive skeletal muscle T2 mapping and compare its performance with 2D and 3D multi-echo spin echo (MESE) for T2 mapping in thigh muscles of healthy subjects.

Methods

The performance of 2D MESE, 3D MESE and the proposed T2prep 3D TSE in the presence of transmit B1 and B0 inhomogeneities was first simulated. The thigh muscles of ten young and healthy subjects were then scanned on a 3 T system and T2 mapping was performed using the three sequences. Transmit B1-maps and proton density fat fraction (PDFF) maps were also acquired. The subjects were scanned three times to assess reproducibility. T2 values were compared among sequences and their sensitivity to B1 inhomogeneities was compared to simulation results. Correlations were also determined between T2 values, PDFF and B1.

Results

The left rectus femoris muscle showed the largest B1 deviations from the nominal value (from 54.2% to 92.9%). Significant negative correlations between T2 values and B1 values were found in the left rectus femoris muscle for 3D MESE (r = -0.72, p<0.001) and 2D MESE (r = -0.71, p<0.001), but not for T2prep 3D TSE (r = -0.32, p = 0.09). Reproducibility of T2 expressed by root mean square coefficients of variation (RMSCVs) were equal to 3.5% in T2prep 3D TSE, 2.6% in 3D MESE and 2.4% in 2D MESE. Significant differences between T2 values of 3D sequences (T2prep 3D TSE and 3D MESE) and 2D MESE were found in all muscles with the highest values for 2D MESE (p<0.05). No significant correlations were found between PDFF and T2 values.

Conclusion

A strong influence of an inhomogeneous B1 field on the T2 values of 3D MESE and 2D MESE was shown, whereas the proposed T2prep 3D TSE gives B1-insensitive and reproducible thigh muscle T2 mapping.

Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease

Quantitative magnetic resonance imaging (qMRI) describes the development and use of MRI to quantify physical, chemical, and/or biological properties of living systems. Neuromuscular diseases often exhibit a temporally varying, spatially heterogeneous, and multi-faceted pathology. The goal of this protocol is to characterize this pathology using qMRI methods. The MRI acquisition protocol begins with localizer images (used to locate the position of the body and tissue of interest within the MRI system), quality control measurements of relevant magnetic field distributions, and structural imaging for general anatomical characterization. The qMRI portion of the protocol includes measurements of the longitudinal and transverse relaxation time constants (T1 and T2, respectively). Also acquired are diffusion-tensor MRI data, in which water diffusivity is measured and used to infer pathological processes such as edema. Quantitative magnetization transfer imaging is used to characterize the relative tissue content of macromolecular and free water protons. Lastly, fat-water MRI methods are used to characterize fibro-adipose tissue replacement of muscle. In addition to describing the data acquisition and analysis procedures, this paper also discusses the potential problems associated with these methods, the analysis and interpretation of the data, MRI safety, and strategies for artifact reduction and protocol optimization.

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.

Magnetic resonance imaging of skeletal muscle disease

Neuromuscular diseases often exhibit a temporally varying, spatially heterogeneous, and multifaceted pathology. The goals of this chapter are to describe and evaluate the use of quantitative magnetic resonance imaging (MRI) methods to characterize muscle pathology. The following criteria are used for this evaluation: objective measurement of continuously distributed variables; clear and well-understood relationship to the pathology of interest; sensitivity to improvement or worsening of clinical status; and the measurement properties of accuracy and precision. Two major classes of MRI methods meet all of these criteria: (1) MRI methods for measuring muscle contractile volume or cross-sectional area by combining structural MRI and quantitative fat-water MRI; and (2) an MRI method for characterizing the edema caused by inflammation, the measurement of the transverse relaxation time constant (T2). These methods are evaluated with respect to the four criteria listed above and examples from neuromuscular disorders are provided. Finally, these methods are summarized and synthesized and recommendations for additional quantitative MRI developments are made.

Localization and quantification of intramuscular damage using statistical parametric mapping and skeletal muscle parcellation

In the present study, we proposed an original and robust methodology which combines the spatial normalization of skeletal muscle images, the statistical parametric mapping (SPM) analysis and the use of a specific parcellation in order to accurately localize and quantify the extent of skeletal muscle damage within the four heads of the quadriceps femoris. T₂ maps of thigh muscles were characterized before, two (D2) and four (D4) days after 40 maximal isometric electrically-evoked contractions in 25 healthy young males. On the basis of SPM analysis of coregistrated T₂ maps, the alterations were similarly detected at D2 and D4 in the superficial and distal regions of the vastus medialis (VM) whereas the proportion of altered muscle was higher in deep muscle regions of the vastus lateralis at D4 (deep: 35 ± 25%, superficial: 23 ± 15%) as compared to D2 (deep: 18 ± 13%, superficial: 17 ± 13%). The present methodology used for the first time on skeletal muscle would be of utmost interest to detect subtle intramuscular alterations not only for the diagnosis of muscular diseases but also for assessing the efficacy of potential therapeutic interventions and clinical treatment strategies.

T2 relaxation times are increased in Skeletal muscle of DMD but not BMD patients

INTRODUCTION

Exon-skipping drugs in Duchenne muscular dystrophy (DMD) aim to restore truncated dystrophin expression, which is present in the milder Becker muscular dystrophy (BMD). MRI skeletal muscle T2 relaxation times as a representation of edema/inflammation could be quantitative outcome parameters for such trials.

METHODS

We studied T2 relaxation times, adjusted for muscle fat fraction using Dixon MRI, in lower leg muscles of DMD and BMD patients and healthy controls.

RESULTS

T2 relaxation times correlated significantly with fat fractions in patients only (P < 0.001). After adjusting for muscle fat, T2 relaxation times were significantly increased in 6 muscles of DMD patients (P < 0.01), except for the extensor digitorum longus. In BMD, T2 relaxation times were unchanged.

CONCLUSIONS

T2 relaxation times could be a useful outcome parameter in exon-skipping trials in DMD but are influenced by fat despite fat suppression. This should be accounted for when using quantitative T2 mapping to investigate edema/inflammation.

MRI biomarker assessment of neuromuscular disease progression: a prospective observational cohort study

BACKGROUND

A substantial impediment to progress in trials of new therapies in neuromuscular disorders is the absence of responsive outcome measures that correlate with patient functional deficits and are sensitive to early disease processes. Irrespective of the primary molecular defect, neuromuscular disorder pathological processes include disturbance of intramuscular water distribution followed by intramuscular fat accumulation, both quantifiable by MRI. In pathologically distinct neuromuscular disorders, we aimed to determine the comparative responsiveness of MRI outcome measures over 1 year, the validity of MRI outcome measures by cross-sectional correlation against functionally relevant clinical measures, and the sensitivity of specific MRI indices to early muscle water changes before intramuscular fat accumulation beyond the healthy control range.

METHODS

We did a prospective observational cohort study of patients with either Charcot-Marie-Tooth disease 1A or inclusion body myositis who were attending the inherited neuropathy or muscle clinics at the Medical Research Council (MRC) Centre for Neuromuscular Diseases, National Hospital for Neurology and Neurosurgery, London, UK. Genetic confirmation of the chromosome 17p11.2 duplication was required for Charcot-Marie-Tooth disease 1A, and classification as pathologically or clinically definite by MRC criteria was required for inclusion body myositis. Exclusion criteria were concomitant diseases and safety-related MRI contraindications. Healthy age-matched and sex-matched controls were also recruited. Assessments were done at baseline and 1 year. The MRI outcomes-fat fraction, transverse relaxation time (T2), and magnetisation transfer ratio (MTR)-were analysed during the 12-month follow-up, by measuring correlation with functionally relevant clinical measures, and for T2 and MTR, sensitivity in muscles with fat fraction less than the 95th percentile of the control group.

FINDINGS

Between Jan 19, 2010, and July 7, 2011, we recruited 20 patients with Charcot-Marie-Tooth disease 1A, 20 patients with inclusion body myositis, and 29 healthy controls (allocated to one or both of the 20-participant matched-control subgroups). Whole muscle fat fraction increased significantly during the 12-month follow-up at calf level (mean absolute change 1.2%, 95% CI 0.5-1.9, p=0.002) but not thigh level (0.2%, -0.2 to 0.6, p=0.38) in patients with Charcot-Marie-Tooth disease 1A, and at calf level (2.6%, 1.3-4.0, p=0.002) and thigh level (3.3%, 1.8-4.9, p=0.0007) in patients with inclusion body myositis. Fat fraction correlated with the lower limb components of the inclusion body myositis functional rating score (ρ=-0.64, p=0.002) and the Charcot-Marie-Tooth examination score (ρ=0.63, p=0.003). Longitudinal T2 and MTR changed consistently with fat fraction but more variably. In muscles with a fat fraction lower than the control group 95th percentile, T2 was increased in patients compared with controls (regression coefficients: inclusion body myositis thigh 4.0 ms [SE 0.5], calf 3.5 ms [0.6]; Charcot-Marie-Tooth 1A thigh 1.0 ms [0.3], calf 2.0 ms [0.3]) and MTR reduced compared with controls (inclusion body myositis thigh -1.5 percentage units [pu; 0.2], calf -1.1 pu [0.2]; Charcot-Marie-Tooth 1A thigh -0.3 pu [0.1], calf -0.7 pu [0.1]).

INTERPRETATION

MRI outcome measures can monitor intramuscular fat accumulation with high responsiveness, show validity by correlation with conventional functional measures, and detect muscle water changes preceding marked intramuscular fat accumulation. Confirmation of our results in further cohorts with these and other muscle-wasting disorders would suggest that MRI biomarkers might prove valuable in experimental trials.

FUNDING

Medical Research Council UK.

The Effects of Spinopelvic Parameters and Paraspinal Muscle Degeneration on S1 Screw Loosening

OBJECTIVE

To investigate risk factors for S1 screw loosening after lumbosacral fusion, including spinopelvic parameters and paraspinal muscles.

METHODS

We studied with 156 patients with degenerative lumbar disease who underwent lumbosacral interbody fusion and pedicle screw fixation including the level of L5-S1 between 2005 and 2012. The patients were divided into loosening and non-loosening groups. Screw loosening was defined as a halo sign larger than 1 mm around a screw. We checked cross sectional area of paraspinal muscles, mean signal intensity of the muscles on T2 weight MRI as a degree of fatty degeneration, spinopelvic parameters, bone mineral density, number of fusion level, and the characteristic of S1 screw.

RESULTS

Twenty seven patients showed S1 screw loosening, which is 24.4% of total. The mean duration for S1 screw loosening was 7.3±4.1 months after surgery. Statistically significant risk factors were increased age, poor BMD, 3 or more fusion levels (p<0.05). Among spinopelvic parameters, a high pelvic incidence (p<0.01), a greater difference between pelvic incidence and lumbar lordotic angle preoperatively (p<0.01) and postoperatively (p<0.05). Smaller cross-sectional area and high T2 signal intensity in both multifidus and erector spinae muscles were also significant muscular risk factors (p<0.05). Small converging angle (p<0.001) and short intraosseous length (p<0.05) of S1 screw were significant screw related risk factors (p<0.05).

CONCLUSION

In addition to well known risk factors, spinopelvic parameters and the degeneration of paraspinal muscles also showed significant effects on the S1 screw loosening.

Quantitative Skeletal Muscle MRI: Part 1, Derived T2 Fat Map in Differentiation Between Boys With Duchenne Muscular Dystrophy and Healthy Boys

OBJECTIVE

The purpose of this study was to validate derived T2 maps as an objective measure of muscular fat for discrimination between boys with Duchenne muscular dystrophy (DMD) and healthy boys.

SUBJECTS AND METHODS

Forty-two boys with DMD (mean age, 9.9 years) and 31 healthy boys (mean age, 11.4 years) were included in the study. Age, body mass index, and clinical function scale grade were evaluated. T1-weighted MR images and T2 maps with and without fat suppression were obtained. Fatty infiltration was graded 0-4 on T1-weighted images, and derived T2 fat values (difference between mean T2 values from T2 maps with and without fat suppression) of the gluteus maximus and vastus lateralis muscles were calculated. Group comparisons were performed. The upper limit of the 95% reference interval of T2 fat values from the control group was applied.

RESULTS

There was no significant difference in age or body mass index between groups. All healthy boys and 19 boys (45.2%) with DMD had a normal clinical function scale grade. Grade 1 fatty infiltration was seen in 90.3% (gluteus maximus) and 71.0% (vastus lateralis) of healthy boys versus 33.3% (gluteus maximus) and 52.4% (vastus lateralis) of boys with DMD. T2 fat values of boys with DMD were significantly longer than in the control group (p < 0.001). Using a 95% reference interval for healthy boys for the gluteus maximus (28.3 milliseconds) allowed complete separation from boys with DMD (100% sensitivity, 100% specificity), whereas the values for the vastus lateralis (7.28 milliseconds) resulted in 83.3% sensitivity and 100% specificity.

CONCLUSION

Measurement of muscular fat with T2 maps is accurate for differentiating boys with DMD from healthy boys.

Longitudinal Evaluation of Muscle Composition Using Magnetic Resonance in 4 Boys With Duchenne Muscular Dystrophy: Case Series

BACKGROUND

Duchenne muscular dystrophy (DMD), an inherited recessive X chromosome-linked disease, is the most severe childhood form of muscular dystrophy. Boys with DMD experience muscle loss, with infiltration of intramuscular fat into muscles.

OBJECTIVES

This case series describes the progression of DMD in boys using magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). Magnetic resonance results are then compared with an established functional timed test.

METHODS

Four boys with DMD and 4 healthy age-matched controls were chosen from a larger cohort. Boys with DMD were assessed at 4 time points over 2 years, with controls assessed at baseline only. Progression of the disease was documented by assessing the plantar flexors using MRI and MRS techniques and by assessing ambulation using the 30-Foot Fast Walk Test.

RESULTS

Transverse relaxation time (T2) values were elevated in all boys with DMD at baseline. The lipid ratio increased rapidly as the disease progressed in 2 boys. Discrete changes in T2 in the other 2 boys with DMD indicated a slower disease progression. Magnetic resonance imaging and MRS allowed monitoring of the disease over all time periods regardless of ambulation status.

LIMITATIONS

The magnetic resonance data were collected with 2 different magnets at 2 different field strengths (1.5 and 3.0 T). Although we corrected for this difference, care must be taken in interpreting data when different image collection systems are used. This was a case series of 4 boys with DMD taken from a larger cohort study.

CONCLUSIONS

Magnetic resonance imaging and MRS are objective, noninvasive techniques for measuring muscle pathology and can be used to detect discrete changes in both people who are ambulatory and those who are nonambulatory. These techniques should be considered when monitoring DMD progression and assessing efficacy of therapeutic interventions.

Longitudinal 2-point dixon muscle magnetic resonance imaging in becker muscular dystrophy

INTRODUCTION

Quantitative MRI techniques detect disease progression in myopathies more sensitively than muscle function measures or conventional MRI. To date, only conventional MRI data using visual rating scales are available for measurement of disease progression in Becker muscular dystrophy (BMD).

METHODS

In 3 patients with BMD (mean age 36.8 years), the mean fat fraction (MFF) of the thigh muscles was assessed by MRI at baseline and at 1-year follow-up using a 2-point Dixon approach (2PD). The motor function measurement scale (MFM) was used for clinical assessment.

RESULTS

The mean MFF of all muscles at baseline was 61.6% (SD 7.6). It increased by 3.7% to 65.3% (SD 4.7) at follow-up. The severity of muscle involvement varied between various muscle groups.

CONCLUSIONS

As in other myopathies, 2PD can quantify fatty muscle degeneration in BMD and can detect disease progression in a small sample size and at relatively short imaging intervals.

Non-invasive MRI and spectroscopy of mdx mice reveal temporal changes in dystrophic muscle imaging and in energy deficits

In Duchenne muscular dystrophy (DMD), a genetic disruption of dystrophin protein expression results in repeated muscle injury and chronic inflammation. Magnetic resonance imaging shows promise as a surrogate outcome measure in both DMD and rehabilitation medicine that is capable of predicting clinical benefit years in advance of functional outcome measures. The mdx mouse reproduces the dystrophin deficiency that causes DMD and is routinely used for preclinical drug testing. There is a need to develop sensitive, non-invasive outcome measures in the mdx model that can be readily translatable to human clinical trials. Here we report the use of magnetic resonance imaging and spectroscopy techniques for the non-invasive monitoring of muscle damage in mdx mice. Using these techniques, we studied dystrophic mdx muscle in mice from 6 to 12 weeks of age, examining both the peak disease phase and natural recovery phase of the mdx disease course. T2 and fat-suppressed imaging revealed significant levels of tissue with elevated signal intensity in mdx hindlimb muscles at all ages; spectroscopy revealed a significant deficiency of energy metabolites in 6-week-old mdx mice. As the mdx mice progressed from the peak disease stage to the recovery stage of disease, each of these phenotypes was either eliminated or reduced, and the cross-sectional area of the mdx muscle was significantly increased when compared to that of wild-type mice. Histology indicates that hyper-intense MRI foci correspond to areas of dystrophic lesions containing inflammation as well as regenerating, degenerating and hypertrophied myofibers. Statistical sample size calculations provide several robust measures with the ability to detect intervention effects using small numbers of animals. These data establish a framework for further imaging or preclinical studies, and they support the development of MRI as a sensitive, non-invasive outcome measure for muscular dystrophy.

Nitric oxide synthase deficiency and the pathophysiology of muscular dystrophy

The secondary loss of neuronal nitric oxide synthase (nNOS) that occurs in dystrophic muscle is the basis of numerous, complex and interacting features of the dystrophic pathology that affect not only muscle itself, but also influence the interaction of muscle with other tissues. Many mechanisms through which nNOS deficiency contributes to misregulation of muscle development, blood flow, fatigue, inflammation and fibrosis in dystrophic muscle have been identified, suggesting that normalization in NO production could greatly attenuate diverse aspects of the pathology of muscular dystrophy through multiple regulatory pathways. However, the relative importance of the loss of nNOS from the sarcolemma versus the importance of loss of total nNOS from dystrophic muscle remains unknown. Although most current evidence indicates that nNOS localization at the sarcolemma is not required to achieve NO-mediated reductions of pathology in muscular dystrophy, the question remains open concerning whether membrane localization would provide a more efficient rescue from features of the dystrophic phenotype.

Multi-parametric MRI characterization of healthy human thigh muscles at 3.0 T - relaxation, magnetization transfer, fat/water, and diffusion tensor imaging

Muscle diseases commonly have clinical presentations of inflammation, fat infiltration, fibrosis, and atrophy. However, the results of existing laboratory tests and clinical presentations are not well correlated. Advanced quantitative MRI techniques may allow the assessment of myo-pathological changes in a sensitive and objective manner. To progress towards this goal, an array of quantitative MRI protocols was implemented for human thigh muscles; their reproducibility was assessed; and the statistical relationships among parameters were determined. These quantitative methods included fat/water imaging, multiple spin-echo T2 imaging (with and without fat signal suppression, FS), selective inversion recovery for T1 and quantitative magnetization transfer (qMT) imaging (with and without FS), and diffusion tensor imaging. Data were acquired at 3.0 T from nine healthy subjects. To assess the repeatability of each method, the subjects were re-imaged an average of 35 days later. Pre-testing lifestyle restrictions were applied to standardize physiological conditions across scans. Strong between-day intra-class correlations were observed in all quantitative indices except for the macromolecular-to-free water pool size ratio (PSR) with FS, a metric derived from qMT data. Two-way analysis of variance revealed no significant between-day differences in the mean values for any parameter estimate. The repeatability was further assessed with Bland-Altman plots, and low repeatability coefficients were obtained for all parameters. Among-muscle differences in the quantitative MRI indices and inter-class correlations among the parameters were identified. There were inverse relationships between fractional anisotropy (FA) and the second eigenvalue, the third eigenvalue, and the standard deviation of the first eigenvector. The FA was positively related to the PSR, while the other diffusion indices were inversely related to the PSR. These findings support the use of these T1 , T2 , fat/water, and DTI protocols for characterizing skeletal muscle using MRI. Moreover, the data support the existence of a common biophysical mechanism, water content, as a source of variation in these parameters.

Examination of effects of corticosteroids on skeletal muscles of boys with DMD using MRI and MRS

OBJECTIVE

To evaluate the effects of corticosteroids on the lower extremity muscles in boys with Duchenne muscular dystrophy (DMD) using MRI and magnetic resonance spectroscopy (MRS).

METHODS

Transverse relaxation time (T2) and fat fraction were measured by MRI/MRS in lower extremity muscles of 15 boys with DMD (age 5.0-6.9 years) taking corticosteroids and 15 corticosteroid-naive boys. Subsequently, fat fraction was measured in a subset of these boys at 1 year. Finally, MRI/MRS data were collected from 16 corticosteroid-naive boys with DMD (age 5-8.9 years) at baseline, 3 months, and 6 months. Five boys were treated with corticosteroids after baseline and the remaining 11 served as corticosteroid-naive controls.

RESULTS

Cross-sectional comparisons demonstrated lower muscle T2 and less intramuscular (IM) fat deposition in boys with DMD on corticosteroids, suggesting reduced inflammation/damage and fat infiltration with treatment. Boys on corticosteroids demonstrated less increase in IM fat infiltration at 1 year. Finally, T2 by MRI/MRS detected effects of corticosteroids on leg muscles as early as 3 months after drug initiation.

CONCLUSIONS

These results demonstrate the ability of MRI/MRS to detect therapeutic effects of corticosteroids in reducing inflammatory processes in skeletal muscles of boys with DMD. Our work highlights the potential of MRI/MRS as a biomarker in evaluating therapeutic interventions in DMD.

Quantitative evaluation of fatty degeneration of the supraspinatus and infraspinatus muscles using T2 mapping

BACKGROUND

Although fatty degeneration of the rotator cuff muscles has been reported to affect the outcomes of rotator cuff repairs, only a few studies have attempted to quantitatively evaluate this degeneration. T2 mapping is a quantitative magnetic resonance imaging technique that potentially evaluates the concentration of fat in muscles. The purpose of this study was to investigate fatty degeneration of the rotator cuff muscles by using T2 mapping, as well as to evaluate the reliability of T2 measurement.

METHODS

We obtained magnetic resonance images including T2 mapping from 184 shoulders (180 patients; 110 male patients [112 shoulders] and 70 female patients [72 shoulders]; mean age, 62 years [range, 16-84 years]). Eighty-three shoulders had no rotator cuff tear (group A), whereas 101 shoulders had tears, of which 62 were incomplete to medium (group B) and 39 were large to massive (group C). T2 values of the supraspinatus and infraspinatus muscles were measured and compared among groups. Intraobserver and interobserver variabilities also were examined.

RESULTS

The mean T2 values of the supraspinatus in groups A, B, and C were 36.3 ± 4.7 milliseconds, 44.2 ± 11.3 milliseconds, and 57.0 ± 18.8 milliseconds, respectively. The mean T2 values of the infraspinatus in groups A, B, and C were 36.1 ± 5.1 milliseconds, 40.0 ± 11.1 milliseconds, and 51.9 ± 18.2 milliseconds, respectively. The T2 value significantly increased with the extent of the tear in both muscles. Both intraobserver and interobserver variabilities were more than 0.99.

CONCLUSION

T2 mapping can be a reliable tool to quantify fatty degeneration of the rotator cuff muscles.

Reproducibility, and age, body-weight and gender dependency of candidate skeletal muscle MRI outcome measures in healthy volunteers

Objectives

Quantitative magnetic resonance imaging (MRI) can potentially meet the pressing need for objective, sensitive, reproducible outcome measures in neuromuscular disease trials. We tested, in healthy volunteers, the consistency, reliability and sensitivity to normal inter-subject variation of MRI methods targeted to lower limb muscle pathology to inform the design of practical but comprehensive MRI outcome measure protocols for use in imminent patient studies.

Methods

Forty-seven healthy volunteers, age 21-81 years, were subject at 3T to three-point Dixon fat-fraction measurement, T₁-relaxometry, T₂-relaxometry and magnetisation transfer ratio (MTR) imaging at mid-thigh and mid-calf level bilaterally. Fifteen subjects underwent repeat imaging at 2 weeks.

Results

Mean between-muscle fat fraction and T₂ differences were small, but significant (p < 0.001). Fat fraction and T₂ correlated positively, and MTR negatively with subject age in both the thigh and calf, with similar significant correlations with weight at thigh level only (p < 0.001 to p < 0.05). Scan-rescan and inter-observer intra-class correlation coefficients ranged between 0.62-0.84 and 0.79-0.99 respectively.

Conclusions

Quantitative lower-limb muscle MRI using readily implementable methods was sensitive enough to demonstrate inter-muscle differences (small in health), and correlations with subject age and weight. In combination with high reliability, this strongly supports the suitability of these methods to provide longitudinal outcome measures in neuromuscular disease treatment trials.

Key points

• Quantitative lower limb muscle MRI provides potential outcome measures in neuromuscular diseases

• Bilateral thigh/calf coverage using sequences sensitive to acute and chronic pathology

• Measurements have excellent scan-rescan and interobserver reliability

• Measurements show small but significant inter-subject age and weight dependency

• Readily implementable sequences suitable for further assessment in patient studies

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-014-3145-6) contains supplementary material, which is available to authorized users.

Assessment of intramuscular lipid and metabolites of the lower leg using magnetic resonance spectroscopy in boys with Duchenne muscular dystrophy

The purpose of this study was to use proton magnetic resonance spectroscopy to assess intramuscular lipid and metabolites of lower leg muscles in boys with Duchenne muscular dystrophy (DMD) and determine its relationship with strength and functional ability. Spectroscopic measurements were obtained from four muscles of the lower leg in 25 boys with DMD (9.2±3.1 years) and 10 healthy boys (10.2±2.6 years). Lipid fractions and metabolite concentrations were also determined. Muscle strength, a timed functional test, and the Modified Brooke Lower Extremity Functional Scale were also determined. Lipid fractions were higher (p<0.01) for the DMD group than healthy subjects for all muscles, and lipid fraction was found to be greater in the older DMD boys. The peroneal muscle demonstrated a significant difference in lipid fraction in all DMD age groups. Lipid fractions in all muscles correlated with functional measures (r=0.52-0.70, p<0.001), with smaller inverse correlations with the strength measure (r=-0.36 to -0.56, p<0.05). These findings provide quantifiable information regarding intramuscular lipid and metabolite levels of different muscles across various age groups in boys with DMD and may be used in determining the effect of interventions in future clinical trials.

Validation of a generic approach to muscle water T2 determination at 3T in fat-infiltrated skeletal muscle

PURPOSE

To introduce a novel method for skeletal muscle water T2 determination in fat-infiltrated tissues, using a tri-exponential fit of the global muscle signal decay.

MATERIALS AND METHODS

In all, 48 patients with various neuromuscular diseases were retrospectively selected and their thigh muscles analyzed. Each patient was imaged using a multispin-echo (MSME) sequence with a 17-echo train. The transmit field (B1+) inhomogeneities were evaluated using the actual flip angle imaging method toward voxel sorting. Muscle water T2 was quantified using a tri-exponential signal decay model. The difference between water T2 of voxels within the same muscle but having different fat ratio was analyzed using nonparametric statistical tests. In addition, we evaluated the correlation between fat ratio and T2 values obtained using both a mono- and tri-exponential approach.

RESULTS

The results showed that muscle water T2 values obtained using a tri-exponential approach combined with B1+ map-based voxel sorting were independent of the fat infiltration degree inside the muscle (R(2) < 0.03). This was not the case using the mono-exponential model, which measured different T2s between voxels of the same muscle but with various fat ratio (R(2) > 0.67; P < 10e(-4) ).

CONCLUSION

The tri-exponential model is an accurate tool to monitor muscle tissue disease activity devoid of bias introduced by fat infiltration.

Objective measurement of minimal fat in normal skeletal muscles of healthy children using T2 relaxation time mapping (T2 maps) and MR spectroscopy

BACKGROUND

Various skeletal muscle diseases result in fatty infiltration, making it important to develop noninvasive biomarkers to objectively measure muscular fat.

OBJECTIVE

We compared T2 relaxation time mapping (T2 maps) and magnetic resonance spectroscopy (MRS) with physical characteristics previously correlated with intramuscular fat to validate T2 maps and MRS as objective measures of skeletal muscle fat.

MATERIALS AND METHODS

We evaluated gluteus maximus muscles in 30 healthy boys (ages 5-19 years) at 3 T with T1-weighted images, T2-W images with fat saturation, T2 maps with and without fat saturation, and MR spectroscopy. We calculated body surface area (BSA), body mass index (BMI) and BMI percentile (BMI %). We performed fat and inflammation grading on T1-W imaging and fat-saturated T2-W imaging, respectively. Mean T2 values from T2 maps with fat saturation were subtracted from T2 maps without fat saturation to determine T2 fat values. We obtained lipid-to-water ratios by MR spectroscopy. Pearson correlation was used to assess relationships between BSA, BMI, BMI %, T2 fat values, and lipid-to-water ratios for each boy.

RESULTS

Twenty-four boys completed all exams; 21 showed minimal and 3 showed no fatty infiltration. None showed muscle inflammation. There was correlation between BSA, BMI, and BMI %, and T2 fat values (P < 0.05), and between BMI and BMI %, and lipid-to-water ratios (P < 0.05). There was strong correlation between T2 fat values and lipid-to-water ratios (P < 0.0001, r = 0.83).

CONCLUSION

T2 maps and MR spectroscopy correlate with physical characteristics associated with fatty infiltration of skeletal muscles, even in microscopic amounts, and validate each other. Both techniques might enable detection of minimal pathological fatty infiltration in children with skeletal muscle disorders.

Longitudinal measurements of MRI-T2 in boys with Duchenne muscular dystrophy: effects of age and disease progression

Duchenne muscular dystrophy (DMD) is characterized by an increased muscle damage and progressive replacement of muscle by noncontractile tissue. Both of these pathological changes can lengthen the MRI transverse proton relaxation time (T2). The current study measured longitudinal changes in T2 and its distribution in the lower leg of 16 boys with DMD (5-13years, 15 ambulatory) and 15 healthy controls (5-13years). These muscles were chosen to allow extended longitudinal monitoring, due to their slow progression compared with proximal muscles in DMD. In the soleus muscle of boys with DMD, T2 and the percentage of pixels with an elevated T2 (⩾2SD above control mean T2) increased significantly over 1year and 2years, while the width of the T2 histogram increased over 2years. Changes in soleus T2 variables were significantly greater in 9-13years old compared with 5-8years old boys with DMD. Significant correlations between the change in all soleus T2 variables over 2years and the change in functional measures over 2years were found. MRI measurement of muscle T2 in boys with DMD is sensitive to disease progression and shows promise as a clinical outcome measure.

Quantitative proton MR techniques for measuring fat

Accurate, precise and reliable techniques for the quantification of body and organ fat distributions are important tools in physiology research. They are critically needed in studies of obesity and diseases involving excess fat accumulation. Proton MR methods address this need by providing an array of relaxometry-based (T1, T2) and chemical shift-based approaches. These techniques can generate informative visualizations of regional and whole-body fat distributions, yield measurements of fat volumes within specific body depots and quantify fat accumulation in abdominal organs and muscles. MR methods are commonly used to investigate the role of fat in nutrition and metabolism, to measure the efficacy of short- and long-term dietary and exercise interventions, to study the implications of fat in organ steatosis and muscular dystrophies and to elucidate pathophysiological mechanisms in the context of obesity and its comorbidities. The purpose of this review is to provide a summary of mainstream MR strategies for fat quantification. The article succinctly describes the principles that differentiate water and fat proton signals, summarizes the advantages and limitations of various techniques and offers a few illustrative examples. The article also highlights recent efforts in the MR of brown adipose tissue and concludes by briefly discussing some future research directions.

Multiparameter MRI analysis of the time course of induced muscle damage and regeneration

PURPOSE

To test the ability of different magnetic resonance imaging (MRI) modalities to discriminate the time course of damage and regeneration in a model of acute, toxin-induced muscle damage.

MATERIALS AND METHODS

We analyzed the time course of tissue and cellular changes in mouse lower limb musculature following localized injection of myotoxin by T2 , magnetization transfer (MT), and diffusion-weighted MRI. We also used T1 -weighted imaging to measure leg muscle volume. In addition, postmortem histological analysis of toxin-injected muscles was compared to uninjected controls.

RESULTS

The damages detected by the MRI modalities are transient and recover within 3 weeks. Muscle water diffusivity and edema measured by leg volume increased within the first hours after injection of the toxin. The rate constant for volume increase was 0.65 ± 0.11 hr(-1) , larger than the increase in T2 (0.045 ± 0.013 hr(-1) ) and change in MT ratio (0.028 ± 0.021 hr(-1) ). During repair phase, the rate constants were much smaller: 0.022 ± 0.004 hr(-1) , 0.013 ± 0.0019 hr(-1) and 0.0042 ± 0.0016 hr(-1) for volume, T2 , and MT ratio, respectively. Histological analyses confirmed the underlying cellular changes that matched the progression of MR images.

CONCLUSION

The kinetics of change in the MRI measurements during the progression of damage and repair shows MRI modalities can be used to distinguish these processes.

Chemical shift-based MRI to measure fat fractions in dystrophic skeletal muscle

PURPOSE

The relationship between fat fractions (FFs) determined based on multiple TE, unipolar gradient echo images and (1) H magnetic resonance spectroscopy (MRS) was evaluated using different models for fat-water decomposition, signal-to-noise ratios, and excitation flip angles.

METHODS

A combination of single-voxel proton spectroscopy ((1) H-MRS) and gradient echo imaging was used to determine muscle FFs in both normal and dystrophic muscles. In order to cover a large range of FFs, the soleus and vastus lateralis muscles of 22 unaffected control subjects, 16 subjects with collagen VI deficiency (COL6), and 71 subjects with Duchenne muscular dystrophy (DMD) were studied. (1) H-MRS-based FF were corrected for the increased muscle (1) H2 O T1 and T2 values observed in dystrophic muscles.

RESULTS

Excellent agreement was found between coregistered FFs derived from gradient echo images fit to a multipeak model with noise bias correction and the relaxation-corrected (1) H-MRS FFs (y = 0.93x + 0.003; R(2)  = 0.96) across the full range of FFs. Relaxation-corrected (1) H-MRS FFs and imaging-based FFs were significantly elevated (P < 0.01) in the muscles of COL6 and DMD subjects.

CONCLUSION

FFs, T2 , and T1 were all sensitive to muscle involvement in dystrophic muscle. MRI offered an additional advantage over single-voxel spectroscopy in that the tissue heterogeneity in FFs could be readily determined.

Magnetic resonance imaging of pediatric muscular disorders: recent advances and clinical applications

This review describes various quantitative magnetic resonance imaging techniques that can be used to objectively analyze the composition (T2 relaxation time mapping, Dixon imaging, and diffusion-weighted imaging), architecture (diffusion tensor imaging), mechanical properties (magnetic resonance elastography), and function (magnetic resonance spectroscopy) of normal and pathologic skeletal muscle in the pediatric population.

Quantitative MRI can detect subclinical disease progression in muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a rare autosomal dominant muscular dystrophy with late onset and slow progression. The aim of this study was to compare different methods of quantitative MRI in the follow-up of OPMD to semiquantitative evaluation of MRI images and to functional parameters. We examined 8 patients with genetically confirmed OPMD and 5 healthy volunteers twice at an interval of 13 months. Motor function measurements (MFM) were assessed. Imaging at 1.5 T (Siemens Magnetom Avanto) comprised two axial slice groups at the largest diameter of thigh and calf and included T1w TSE, 2-point Dixon for muscular fat fraction (MFF) and a multi-contrast TSE sequence to calculate quantitative T2 values. T1 images were analyzed using Fischer's semiquantitative 5-point (0–4) scale. MFM and visual scores showed no significant difference over the study period. Overall T2 values increased in patients over the study period from 49.4 to 51.6 ms, MFF increased from 19.2 to 20.7%. Neither T2 values nor MFF increased in controls. Changes in T2 correlated with the time interval between examinations (r 2 = 0.42). In this small pilot trial, it was shown that quantitative muscle MRI can detect subclinical changes in patients with OPMD. Quantitative MRI might, therefore, be a useful tool for monitoring disease progression in future therapeutic trials.

T₂ mapping provides multiple approaches for the characterization of muscle involvement in neuromuscular diseases: a cross-sectional study of lower leg muscles in 5-15-year-old boys with Duchenne muscular dystrophy

Skeletal muscles of children with Duchenne muscular dystrophy (DMD) show enhanced susceptibility to damage and progressive lipid infiltration, which contribute to an increase in the MR proton transverse relaxation time (T₂). Therefore, the examination of T₂ changes in individual muscles may be useful for the monitoring of disease progression in DMD. In this study, we used the mean T₂, percentage of elevated pixels and T₂ heterogeneity to assess changes in the composition of dystrophic muscles. In addition, we used fat saturation to distinguish T₂ changes caused by edema and inflammation from fat infiltration in muscles. Thirty subjects with DMD and 15 age-matched controls underwent T₂ -weighted imaging of their lower leg using a 3-T MR system. T₂ maps were developed and four lower leg muscles were manually traced (soleus, medial gastrocnemius, peroneal and tibialis anterior). The mean T₂ of the traced regions of interest, width of the T₂ histograms and percentage of elevated pixels were calculated. We found that, even in young children with DMD, lower leg muscles showed elevated mean T₂, were more heterogeneous and had a greater percentage of elevated pixels than in controls. T₂ measures decreased with fat saturation, but were still higher (P < 0.05) in dystrophic muscles than in controls. Further, T₂ measures showed positive correlations with timed functional tests (r = 0.23-0.79). The elevated T₂ measures with and without fat saturation at all ages of DMD examined (5-15 years) compared with unaffected controls indicate that the dystrophic muscles have increased regions of damage, edema and fat infiltration. This study shows that T₂ mapping provides multiple approaches that can be used effectively to characterize muscle tissue in children with DMD, even in the early stages of the disease. Therefore, T₂ mapping may prove to be clinically useful in the monitoring of muscle changes caused by the disease process or by therapeutic interventions in DMD.