The impact of diffusion tensor imaging tractography settings on muscle fascicle architecture and diffusion parameter estimates: Tract length, completion, and curvature are most sensitive to tractography settings.

Diffusion-tensor (DT)-MRI tractography provides information about properties relevant to muscle health and function, including estimates of architectural properties such as fascicle length, pennation angle, and curvature and diffusion properties such as mean diffusivity (MD) and fractional anisotropy (FA). Tractography settings, including integration algorithms, thresholds for early tract termination, and tract smoothing approaches, impact the accuracy of the muscle property estimates. However, muscle DT-MRI tractography is performed using a variety of these settings, complicating comparisons between different studies. The effects of different tractography settings on muscle architecture estimates have not been fully explored, and optimized settings for muscle tractography have not yet been determined. We examined the influence of integration algorithm and termination check settings combined with a range of step sizes, termination criteria, and smoothing polynomial orders on tract characteristics, completion/reason for termination, and goodness of fit between fiber tracts and smoothing polynomials using 3-T DT-MR images of the lower leg muscles of seven healthy adults. We found that tract length and completion were highly sensitive to strict FA and intersegment angle thresholds (25%-69% reduction in complete fiber tracts from lowest to highest minimum FA threshold and 11%-36% reduction from highest to lowest intersegment angle threshold). Higher order polynomials (third and fourth order vs. second order) better fit the muscle fiber trajectories, but curvature estimates were highly sensitive to smoothing polynomial order (3.9-6.6 m-1 increase for second- vs. fourth-order fitting polynomials). Step size impacted curvature estimates, albeit to a lesser degree. Integration algorithm had little impact, and mean pennation angle, and tract-based FA and MD, were relatively insensitive to all parameters. The results demonstrate which muscle diffusion measures and architectural estimates are most sensitive to varying tractography settings and support the need for consistent reporting of tractography details to aid interpretation and comparison of results between studies.

A registration strategy to characterize DTI-observed changes in skeletal muscle architecture due to passive shortening.

Skeletal muscle architecture is a key determinant of muscle function. Architectural properties such as fascicle length, pennation angle, and curvature can be characterized using Diffusion Tensor Imaging (DTI), but acquiring these data during a contraction is not currently feasible. However, an image registration-based strategy may be able to convert muscle architectural properties observed at rest to their contracted state. As an initial step toward this long-term objective, the aim of this study was to determine if an image registration strategy could be used to convert the whole-muscle average architectural properties observed in the extended joint position to those of a flexed position, following passive rotation. DTI and high-resolution fat/water scans were acquired in the lower leg of seven healthy participants on a 3T MR system in +20° (plantarflexion) and -10° (dorsiflexion) foot positions. The diffusion and anatomical images from the two positions were used to propagate DTI fiber-tracts from seed points along a mesh representation of the aponeurosis of fiber insertion. The -10° and +20° anatomical images were registered and the displacement fields were used to transform the mesh and fiber-tracts from the +20° to the -10° position. Student's paired t-tests were used to compare the mean architectural parameters between the original and transformed fiber-tracts. The whole-muscle average fiber-tract length, pennation angle, curvature, and physiological cross-sectional areas estimates did not differ significantly. DTI fiber-tracts in plantarflexion can be transformed to dorsiflexion position without significantly affecting the average architectural characteristics of the fiber-tracts. In the future, a similar approach could be used to evaluate muscle architecture in a contracted state.

Predicted effects of image acquisition and analysis conditions on DTMRI tractography-based muscle architecture estimates.

PURPOSE: To quantify the effects of the intrinsic signal pattern, image acquisition conditions, and data analysis conditions on diffusion-tensor MRI (DTMRI) tractography-based muscle architecture estimates using a sampling-reconstruction assessment framework. METHODS: Numerical models of muscles were constructed with realistic architectural properties. DTMRI signals were computed at signal-to-noise ratio (SNR) of 24-96 and common voxel sizes. Fiber tracking was performed, and the results were compared with the known architectural properties. RESULTS: SNR exerted the most significant impact on the outcome. The outcome variables approached asymptotes at SNR ≈ 54. Large in-plane voxel dimensions reduced the similarity between reconstructed fibers and the known architectural properties. Higher order polynomials helped reconstruct fibers with more complicated geometry but overfit noise for less complex geometries. The intrinsic fiber curvature also affected the robustness of polynomial smoothing to SNR. Other conditions, such as the fiber dimensionality, voxel aspect ratio, and slice thickness, did not affect the outcomes. CONCLUSION: SNR ≥ 54 is recommended for accurate muscle architecture characterization using DTMRI. Averaged across all simulated conditions, the greatest percent errors under SNR = 54 were -5.6% and -4.0% for the pennation angle and fiber-tract length estimates, respectively. For fiber tracts with intermediate intrinsic curvature, the greatest percent error for the curvature estimate was 9.8% for SNR = 54. Smaller in-plane voxel size (≤1.5 mm) is preferred to minimize the estimation error in architectural properties. If necessary, slice thickness may be adjusted within typical ranges to achieve sufficient SNR when slices are aligned near the fiber direction. Third-order polynomial fitting is appropriate for smoothing fiber tracts.

Assessment of Mechanically Induced Changes in Helical Fiber Microstructure Using Diffusion Tensor Imaging.

Noninvasive methods to detect microstructural changes in collagen-based fibrous tissues are necessary to differentiate healthy from damaged tissues in vivo but are sparse. Diffusion Tensor Imaging (DTI) is a noninvasive imaging technique used to quantitatively infer tissue microstructure with previous work primarily focused in neuroimaging applications. Yet, it is still unclear how DTI metrics relate to fiber microstructure and function in musculoskeletal tissues such as ligament and tendon, in part because of the high heterogeneity inherent to such tissues. To address this limitation, we assessed the ability of DTI to detect microstructural changes caused by mechanical loading in tissue-mimicking helical fiber constructs of known structure. Using high-resolution optical and micro-computed tomography imaging, we found that static and fatigue loading resulted in decreased sample diameter and a re-alignment of the macro-scale fiber twist angle similar with the direction of loading. However, DTI and micro-computed tomography measurements suggest microstructural differences in the effect of static versus fatigue loading that were not apparent at the bulk level. Specifically, static load resulted in an increase in diffusion anisotropy and a decrease in radial diffusivity suggesting radially uniform fiber compaction. In contrast, fatigue loads resulted in increased diffusivity in all directions and a change in the alignment of the principal diffusion direction away from the constructs' main axis suggesting fiber compaction and microstructural disruptions in fiber architecture. These results provide quantitative evidence of the ability of DTI to detect mechanically induced changes in tissue microstructure that are not apparent at the bulk level, thus confirming its potential as a noninvasive measure of microstructure in helically architected collagen-based tissues, such as ligaments and tendons.

Cardiac magnetic resonance assessment of acute rejection and cardiac allograft vasculopathy in pediatric heart transplant.

BACKGROUND: In pediatric heart transplant (PHT), cardiac catheterization with endomyocardial biopsy (EMB) is standard for diagnosing acute rejection (AR) and cardiac allograft vasculopathy (CAV) but is costly and invasive. OBJECTIVES: To evaluate the ability of cardiac magnetic resonance (CMR) to noninvasively identify differences in PHT patients with AR and CAV. METHODS: Patients were enrolled at three children's hospitals. Data were collected from surveillance EMB or EMB for-cause AR. Patients were excluded if they had concurrent diagnoses of AR and CAV, CMR obtained >7days from AR diagnosis, they had EMB negative AR, or could not undergo contrasted, unsedated CMR. Kruskal-Wallis test was used to compare groups: (1) No AR or CAV (Healthy), (2) AR, (3) CAV. Wilcoxon rank-sum test was used for pairwise comparisons. RESULTS: Fifty-nine patients met inclusion criteria (median age 17years [IQR 15-19]) 10 (17%) with AR, and 11 (19%) with CAV. AR subjects had worse left ventricular ejection fraction compared to Healthy patients (p = 0.001). Global circumferential strain (GCS) was worse in AR (p = 0.054) and CAV (p = 0.019), compared to Healthy patients. ECV, native T1, and T2 z-scores were elevated in patients with AR. CONCLUSIONS: CMR was able to identify differences between CAV and AR. CAV subjects had normal global function but abnormal GCS which may suggest subclinical dysfunction. AR patients have abnormal function and tissue characteristics consistent with edema (elevated ECV, native T1 and T2 z-scores). Characterization of CMR patterns is critical for the development of noninvasive biomarkers for PHT and may decrease dependence on EMB.

Quantitative Muscle Fascicle Tractography Using Brightness-Mode Ultrasound.

A muscle's architecture, defined as the geometric arrangement of its fibers with respect to its mechanical line of action, impacts its abilities to produce force and shorten or lengthen under load. Ultrasound and other noninvasive imaging methods have contributed significantly to our understanding of these structure-function relationships. The goal of this work was to develop a MATLAB toolbox for tracking and mathematically representing muscle architecture at the fascicle scale, based on brightness-mode ultrasound imaging data. The MuscleUS_Toolbox allows user-performed segmentation of a region of interest and automated modeling of local fascicle orientation; calculation of streamlines between aponeuroses of origin and insertion; and quantification of fascicle length, pennation angle, and curvature. A method is described for optimizing the fascicle orientation modeling process, and the capabilities of the toolbox for quantifying and visualizing fascicle architecture are illustrated in the human tibialis anterior muscle. The toolbox is freely available.

Cardiothoracic and Vascular Surgery Implant Compatibility With Ultrahigh Field Magnetic Resonance Imaging (4.7 Tesla and 7 Tesla).

The use of 7 Tesla (T) magnetic resonance imaging (MRI) is expanding across medical specialties, particularly, clinical neurosciences and orthopedics. Investigational 7 T MRI has also been performed in cardiology. A limiting factor for expansion of the role of 7 T, irrespective of the body part being imaged, is the sparse testing of biomedical implant compatibility at field strengths >3 T. Implant compatibility can be tested following the American Society for Testing and Materials International guidelines. To assess the current state of cardiovascular implant safety at field strengths >3 T, a systematic search was performed using PubMed, Web of Science, and citation matching. Studies written in English that included at least 1 cardiovascular-related implant and at least 1 safety outcome (deflection angle, torque, or temperature change) were included. Data were extracted for the implant studied, implant composition, deflection angle, torque, and temperature change, and the American Society for Testing and Materials International standards were followed. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses reporting guidelines for scoping reviews were followed. A total of 9 studies were included. A total of 34 cardiovascular-related implants tested ex vivo at 7 T and 91 implants tested ex vivo at 4.7 T were included. The implants included vascular grafts and conduits, vascular access ports, peripheral and coronary stents, caval filters, and artificial valves. A total of 2 grafts, 1 vascular access port, 2 vena cava filters, and 5 stents were identified as incompatible with the 7 T MRI. All incompatible stents were 40 mm in length. Based on the safety outcomes reported, we identify several implants that may be compatible with >3 T MRI. This scoping review seeks to concisely summarize all the cardiovascular-related implants tested for ultrahigh field MRI compatibility to date.

Feasibility of joint mapping of triglyceride saturation and water longitudinal relaxation in a single breath hold applied to high fat-fraction adipose depots in the periclavicular anatomy.

INTRODUCTION: Simultaneous mapping of triglyceride (TAG) saturation and tissue water relaxation may improve the characterization of the structure and function of anatomies with significant adipose tissue. While several groups have demonstrated in vivo TAG saturation imaging using MRI, joint mapping of relaxation and TAG saturation is understudied. Such mappings may avoid bias from physiological motion, if they can be done within a single breath-hold, and also account for static and applied magnetic field heterogeneity. METHODS: We propose a transient-state/MR fingerprinting single breath-hold sequence at 3 T, a low-rank reconstruction, and a parameter estimation pipeline that jointly estimates the number of double bonds (NDB), number of methylene interrupted double bonds (NMIDB), and tissue water T1, while accounting for non-ideal radiofrequency transmit scaling and off-resonance effects. We test the proposed method in simulations, in phantom against MR spectroscopy (MRS), and in vivo regions in and around high fat fraction (FF) periclavicular adipose tissue. Partial volume and multi-peak transverse relaxation effects are explored. RESULTS: The simulation results demonstrate accurate NDB, NMIDB, and water T1 estimates across a range of NDB, NMIDB, and T1 values. In phantoms, the proposed method's estimates of NDB and NMIDB correlate with those from MR spectroscopy (Pearson correlation ≥0.98), while the water T1 estimates are concordant with a standard phantom. The NDB and NMIDB are sensitive to partial volumes of water, showing increasing bias at FF < 40%. This bias is found to be due to noise and transverse relaxation effects. The in vivo periclavicular adipose tissue has high FF (>90%). The adipose tissue NDB and NMIDB, and muscle T1 estimates are comparable to those reported in the literature. CONCLUSION: Robust estimation of NDB, NMIDB at high FF and water T1 across a broad range of FFs are feasible using the proposed methods. Further reduction of noise and model bias are needed to employ the proposed technique in low FF anatomies and pathologies.

Neurosurgical Implant Safety in 7 T MRI: A Scoping Review.

The use of 7 Tesla (T) magnetic resonance imaging (MRI) is expanding across neurosurgical and neurologic specialties. However, few neurosurgical-related implants have been tested for safety at 7 T, limiting its use in patients with cranial fixation, shunt placements, and other implants. Implant safety can be determined via the American Society for Testing Materials International (ASTM) guidelines. To assess the current state of neurosurgical implant safety at 7 T, a systematic search was performed using PubMed, MEDLINE, Web of Knowledge, and citation matching. Studies written in English that included at least one neurosurgical implant and at least one safety outcome were included. Data were extracted for implant studied, implant composition, deflection angle, torque, temperature change, and ASTM guidelines followed. PRISMA reporting guidelines for scoping reviews were followed. Overall, 18 studies consisting of 45 unique implants were included. Implants included cranial fixation devices, aneurysm clips, spinal rods, pedicle screws, ventriculoperitoneal (VP) shunts, deep brain stimulation devices, and electroencephalogram (EEG) caps and electrodes. Cranial fixation devices, deep brain stimulation devices, spinal rods, and pedicle screws are likely 7 T MRI compatible based on outcomes reported. Aneurysm clips and EEG devices had variable safety outcomes. The VP shunts studied lost functionality after 7 T MRI exposure. We identified several implants that are likely compatible with 7 T MRI. Given the growth in 7 T imaging and expansion of the technology, neurosurgical implants should be constructed with the aforementioned considerations. Caution must be taken with all implants, especially aneurysm clips, programmable VP shunts, and EEG recording devices. It is also noteworthy that several implant testing reports did not report following ASTM standards. This scoping review seeks to concisely summarize all neurosurgical-related implants that have been tested for safety in 7 T MRI. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.

Leveraging cardiac magnetic resonance imaging to assess skeletal muscle progression in Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is characterized by muscle deterioration and progressive weakness. As a result, patients with DMD have significant cardiopulmonary morbidity and mortality that worsens with age and loss of ambulation. Since most validated muscle assessments require ambulation, new functional measures of DMD progression are needed. Despite several evaluation methods available for monitoring disease progression, the relationship between these measures is unknown. We sought to assess the correlation between imaging metrics obtained from cardiac magnetic resonance imaging (CMR) and functional assessments including quantitative muscle testing (QMT), spirometry, and accelerometry. Forty-nine patients with DMD were enrolled and underwent CMR, accelerometry and QMT at baseline, 1-year and 2-year clinic visits with temporally associated pulmonary function testing obtained from the medical record. Imaging of the upper extremity musculature (triceps and biceps) demonstrated the most robust correlations with accelerometry (p<0.03), QMT (p<0.02) and spirometry (p<0.01). T1-mapping of serratus anterior muscle showed a similar, but slightly weaker relationship with accelerometry and QMT. T2-mapping of serratus anterior demonstrated weak indirect correlation with aspects of accelerometry. These images are either routinely obtained in standard CMR or can be added to a protocol and may allow for a more comprehensive assessment of a patient's disease progression.

A MATLAB toolbox for muscle diffusion-tensor MRI tractography.

Diffusion-tensor MRI fiber tractography has been used to reconstruct skeletal muscle architecture, but remains a specialized technique using custom-written data processing routines. In this work, we describe the public release of a software toolbox having the following design objectives: accomplish the pre-processing tasks of file input, image registration, denoising, and diffusion-tensor calculation; allow muscle-specific methods for defining seed points; make fiber-tract architectural measurements referenced to tendinous structures; visualize fiber tracts and other muscle structures of interest; analyze the goodness of outcomes; and provide a programming structure that allows the addition of new capabilities in future versions. The proper function of the code was verified using simulated datasets. The toolbox capabilities for characterizing human muscle structure in vivo were demonstrated in a case study. These capabilities included measurements of muscle morphology; contractile and non-contractile tissue volumes; fiber-tract length, pennation angle, curvature; and the physiological cross-sectional area,. The free public release of this software is a first step in creating of a community of users who use these tools in studies of muscle physiology and biomechanics. Users may further contribute to code development. Along with simulated and actual datasets for benchmarking, these tools will further create mechanisms for enhancing scientific rigor and developing and validating new code features. Planned future developments include additional options for image pre-processing, development of a graphical user interface, analysis of architectural patterns during muscle contraction, and integration of functional imaging data.

Chemical exchange rotation transfer imaging of phosphocreatine in muscle.

In chemical exchange saturation transfer (CEST) imaging, the signal at 2.6 ppm from the water resonance in muscle has been assigned to phosphocreatine (PCr). However, this signal has limited specificity for PCr since the signal is also sensitive to exchange with protein and macromolecular protons when using some conventional quantification methods, and will vary with changes in the water longitudinal relaxation rate. Correcting for these effects while maintaining reasonable acquisition times is challenging. As an alternative approach to overcome these problems, here we evaluate chemical exchange rotation transfer (CERT) imaging of PCr in muscle at 9.4 T. Specifically, the CERT metric, AREXdouble,cpw at 2.6 ppm, was measured in solutions containing the main muscle metabolites, in tissue homogenates with controlled PCr content, and in vivo in rat leg muscles. PCr dominates CERT metrics around 2.6 ppm (although with nontrivial confounding baseline contributions), indicating that CERT is well-suited to PCr specific imaging, and has the added benefit of requiring a relatively small number of acquisitions.

Slice-selective extended phase graphs in gradient-crushed, transient-state free precession sequences: An application to MR fingerprinting.

PURPOSE: Slice-selective, gradient-crushed, transient-state sequences such as those used in MR fingerprinting (MRF) relaxometry are sensitive to slice profile effects. Whereas balanced steady-state free precession MRF profile effects have been studied, less attention has been given to gradient-crushed MRF forms. Extensions of the extended phase graph (EPG) formalism, called slice-selective EPG (ssEPG), are proposed that model slice profile effects. THEORY AND METHODS: The hard-pulse approximation to slice-selective excitation in the spatial domain is reformulated in k-space. Excitation is modeled by standard EPG shift and transition operators. This ssEPG modeling is validated against Bloch simulations and phantom slice profile measurements. ssEPG relaxometry accuracy and variability are compared with other EPG methods in phantoms and human leg in vivo. The role of ∆B0 interactions with slice profile and gradient crushers is investigated. RESULTS: Simulations and slice profile measurements show that ssEPG can model highly dynamic slice profile effects of gradient-crushed sequences. The MRF ssEPG T2 estimates over 0 < T2 < 100 ms improve accuracy by > 10 ms at some values relative to other modeling approaches. Small deviations in B0 can produce substantial bias in T2 estimations from a range of MRF sequence types, and these effects can be modeled and understood by ssEPG. CONCLUSION: Transient-state, gradient-crushed sequences such as those used in MRF are sensitive to slice profile effects, and these effects depend on RF pulse choice, gradient crusher strength, and ∆B0 . It was found ssEPG was the most accurate EPG-based means to model these effects.

Beyond ambulation: Measuring physical activity in youth with Duchenne muscular dystrophy.

Patients with Duchenne muscular dystrophy (DMD) develop skeletal muscle weakness and cardiomyopathy. Validated skeletal muscle outcome measures are limited to ambulatory patients, but most DMD patients in cardiac trials are non-ambulatory. New objective functional assessments are needed. This study's objective was to assess the correlation and longitudinal change of two measures: quantitative muscle testing (QMT) and accelerometry. Patients with DMD were prospectively enrolled and underwent QMT and wore wrist and ankle accelerometers for seven days at baseline, 1-, and 2-years. QMT measures were indexed to age. Accelerometer recordings were total vector magnitudes and awake vector magnitude. Correlations were assessed using a Spearman correlation, and longitudinal change was evaluated using a paired t-test or a Wilcoxon signed rank test. Forty-eight participants were included. QMT and accelerometry measures had a moderate or strong correlation, particularly indexed arm QMT with total wrist vector magnitude (rho=0.85, p<0.001), total indexed QMT with total wrist vector magnitude (rho=0.8, p<0.001) and indexed leg QMT with total ankle vector magnitude (rho=0.69, p<0.001). QMT and accelerometry measures declined significantly over time. Accelerometry correlates with QMT and indexed QMT in boys with DMD. A combination of QMT and accelerometry may provide a complementary assessment of skeletal muscle function in non-ambulatory boys with DMD.

Cold exposure induces dynamic, heterogeneous alterations in human brown adipose tissue lipid content.

Brown adipose tissue undergoes a dynamic, heterogeneous response to cold exposure that can include the simultaneous synthesis, uptake, and oxidation of fatty acids. The purpose of this work was to quantify these changes in brown adipose tissue lipid content (fat-signal fraction (FSF)) using fat-water magnetic resonance imaging during individualized cooling to 3 °C above a participant's shiver threshold. Eight healthy men completed familiarization, perception-based cooling, and MRI-cooling visits. FSF maps of the supraclavicular region were acquired in thermoneutrality and during cooling (59.5 ± 6.5 min). Brown adipose tissue regions of interest were defined, and voxels were grouped into FSF decades (0-10%, 10-20%…90-100%) according to their initial value. Brown adipose tissue contained a heterogeneous morphology of lipid content. Voxels with initial FSF values of 60-100% (P < 0.05) exhibited a significant decrease in FSF while a simultaneous increase in FSF occurred in voxels with initial FSF values of 0-30% (P < 0.05). These data suggest that in healthy young men, cold exposure elicits a dynamic and heterogeneous response in brown adipose tissue, with areas initially rich with lipid undergoing net lipid loss and areas of low initial lipid undergoing a net lipid accumulation.

MR fingerprinting with simultaneous T1, T2, and fat signal fraction estimation with integrated B0 correction reduces bias in water T1 and T2 estimates.

PURPOSE: MR fingerprinting (MRF) sequences permit efficient T1 and T2 estimation in cranial and extracranial regions, but these areas may include substantial fat signals that bias T1 and T2 estimates. MRI fat signal fraction estimation is also a topic of active research in itself, but may be complicated by B0 heterogeneity and blurring during spiral k-space acquisitions, which are commonly used for MRF. An MRF method is proposed that separates fat and water signals, estimates water T1 and T2, and accounts for B0 effects with spiral blurring correction, in a single sequence. THEORY AND METHODS: A k-space-based fat-water separation method is further extended to unbalanced steady-state free precession MRF with swept echo time. Repeated application of this k-space fat-water separation to demodulated forms of the measured data allows a B0 map and correction to be approximated. The method is compared with MRF without fat separation across a broad range of fat signal fractions (FSFs), water T1s and T2s, and under heterogeneous static fields in simulations, phantoms, and in vivo. RESULTS: The proposed method's FSF estimates had a concordance correlation coefficient of 0.990 with conventional measurements, and reduced biases in the T1 and T2 estimates due to fat signal relative to other MRF sequences by several hundred ms. The B0 correction improved the FSF, T1, and T2 estimation compared to those estimates without correction. CONCLUSION: The proposed method improves MRF water T1 and T2 estimation in the presence of fat and provides accurate FSF estimation with inline B0 correction.

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.

Fat-Water Phantoms for Magnetic Resonance Imaging Validation: A Flexible and Scalable Protocol.

As new techniques are developed to image adipose tissue, methods to validate such protocols are becoming increasingly important. Phantoms, experimental replicas of a tissue or organ of interest, provide a low cost, flexible solution. However, without access to expensive and specialized equipment, constructing stable phantoms with high fat fractions (e.g., >50% fat fraction levels such as those seen in brown adipose tissue) can be difficult due to the hydrophobic nature of lipids. This work presents a detailed, low cost protocol for creating 5x 100 mL phantoms with fat fractions of 0%, 25%, 50%, 75%, and 100% using basic lab supplies (hotplate, beakers, etc.) and easily accessible components (distilled water, agar, water-soluble surfactant, sodium benzoate, gadolinium-diethylenetriaminepentacetate (DTPA) contrast agent, peanut oil, and oil-soluble surfactant). The protocol was designed to be flexible; it can be used to create phantoms with different fat fractions and a wide range of volumes. Phantoms created with this technique were evaluated in the feasibility study that compared the fat fraction values from fat-water magnetic resonance imaging to the target values in the constructed phantoms. This study yielded a concordance correlation coefficient of 0.998 (95% confidence interval: 0.972-1.00). In summary, these studies demonstrate the utility of fat phantoms for validating adipose tissue imaging techniques across a range of clinically relevant tissues and organs.

Increased Number of Circulating CD8/CD26 T Cells in the Blood of Duchenne Muscular Dystrophy Patients Is Associated with Augmented Binding of Adenosine Deaminase and Higher Muscular Strength Scores.

Duchenne muscular dystrophy (DMD) is an X-linked disorder that leads to cardiac and skeletal myopathy. The complex immune activation in boys with DMD is incompletely understood. To better understand the contribution of the immune system into the progression of DMD, we performed a systematic characterization of immune cell subpopulations obtained from peripheral blood of DMD subjects and control donors. We found that the number of CD8 cells expressing CD26 (also known as adenosine deaminase complexing protein 2) was increased in DMD subjects compared to control. No differences, however, were found in the levels of circulating factors associated with pro-inflammatory activation of CD8/CD26 cells, such as tumor necrosis factor-α (TNFα), granzyme B, and interferon-γ (IFNγ). The number of CD8/CD26 cells correlated directly with quantitative muscle testing (QMT) in DMD subjects. Since CD26 mediates binding of adenosine deaminase (ADA) to the T cell surface, we tested ADA-binding capacity of CD8/CD26 cells and the activity of bound ADA. We found that mononuclear cells (MNC) obtained from DMD subjects with an increased number of CD8/CD26 T cells had a greater capacity to bind ADA. In addition, these MNC demonstrated increased hydrolytic deamination of adenosine to inosine. Altogether, our data demonstrated that (1) an increased number of circulating CD8/CD26 T cells is associated with preservation of muscle strength in DMD subjects, and (2) CD8/CD26 T cells from DMD subjects mediated degradation of adenosine by adenosine deaminase. These results support a role for T cells in slowing the decline in skeletal muscle function, and a need for further investigation into contribution of CD8/CD26 T cells in the regulation of chronic inflammation associated with DMD.