Muscle changes detected with diffusion-tensor imaging after long-distance running

Metabolic and Structural Skeletal Muscle Health in Systemic Lupus Erythematosus-Related Fatigue: A Multimodal Magnetic Resonance Imaging Study

OBJECTIVE

To investigate the potential structural and metabolic role of skeletal muscle in systemic lupus erythematosus (SLE)-related fatigue.

METHODS

A case-control, multimodal magnetic resonance imaging (MRI) study was conducted. Cases were patients with inactive SLE who reported chronic fatigue. Controls were age- and sex-matched healthy members of the general population. Patients were clinically characterized and then underwent a 3T whole-body MRI scan. Resting and dynamic ³¹ P MRI spectroscopy of the calf muscles was applied, from which phosphocreatine (PCr) recovery halftime, a marker of mitochondrial dysfunction, was computed. In addition, microstructural sequences (T1-weighted anatomic images, T2 mapping, and diffusion tensor imaging) were acquired. Descriptive statistics evaluated group differences and within-case physical fatigue correlations were explored.

RESULTS

Of the 37 recruits (mean age 43.8 years, 89.2% female), cases (n = 19) reported higher levels of physical fatigue, pain, depression, and sleep disturbance compared to the control group (P < 0.0001). PCr was greater (P = 0.045) among cases (mean ± SD 33.0 ± 9.0 seconds) compared to controls (mean ± SD 27.1 ± 6.6 seconds). No microstructural group differences were observed. Within cases, physical fatigue did not correlate with PCr (r = -0.28, P = 0.25).

CONCLUSION

We report preliminary data demonstrating greater skeletal muscle mitochondrial dysfunction among fatigued patients with SLE compared to healthy controls.

Quantitative MRI Reveals Microstructural Changes in the Upper Leg Muscles After Running a Marathon

Background

The majority of sports‐related injuries involve skeletal muscle. Unlike acute trauma, which is often caused by a single traumatic event leading to acute symptoms, exercise‐induced microtrauma may remain subclinical and difficult to detect. Therefore, novel methods to detect and localize subclinical exercise‐induced muscle microtrauma are desirable.

Purpose

To assess acute and delayed microstructural changes in upper leg muscles with multiparametric quantitative MRI after running a marathon.

Study Type

Longitudinal; 1‐week prior, 24–48 hours postmarathon and 2‐week follow‐up

Population

Eleven men participants (age: 47–68 years).

Field Strength/Sequence

Spin‐echo echo planar imaging (SE‐EPI) with diffusion weighting, multispin echo, Dixon, and fat‐suppressed turbo spin‐echo (TSE) sequences at 3T. MR datasets and creatine kinase (CK) concentrations were obtained at three timepoints.

Assessment

Diffusion parameters, perfusion fractions, and quantitative (q)T₂ values were determined for hamstring and quadriceps muscles, TSE images were scored for acute injury. The vastus medialis and biceps femoris long head muscles were divided and analyzed in five segments to assess local damage.

Statistical Tests

Differences between timepoints in MR parameters were assessed with a multilevel linear mixed model and in CK concentrations with a Friedman test. Mean diffusivity (MD) and qT₂ for whole muscle and muscle segments were compared using a multivariate analysis of covariance (MANCOVA).

Results

CK concentrations were elevated (1194 U/L [166–3906], P < 0.001) at 24–48 hours postmarathon and returned to premarathon values (323 U/L [56–2216]) at 2‐week follow‐up. Most of the MRI diffusion indices in muscles without acute injury changed at 24–48 hours postmarathon and returned to premarathon values at follow‐up (MD, RD, and λ3; P < 0.006). qT₂ values (P = 0.003) and perfusion fractions (P = 0.003) were higher at baseline compared to follow‐up. Local assessments of MD and qT₂ revealed more pronounced changes than whole muscle assessment (2–3‐fold; P < 0.01).

Data Conclusion

Marathon running‐induced microtrauma was detected with MRI in individual whole upper leg muscles and even more pronounced on local segments.

Level of Evidence

2

Technical Efficacy Stage

3 J. Magn. Reson. Imaging 2020;52:407–417.

Diffusion tensor imaging combined with T2 mapping to quantify changes in the skeletal muscle associated with training and endurance exercise in competitive triathletes

OBJECTIVES

Diffusion tensor magnetic resonance imaging (DTI) and T2 mapping enable the detection of exercise-induced changes in the skeletal muscle microenvironment. This study prospectively quantified DTI metrics and T2 relaxation times of thigh muscles in competitive triathletes at rest and following a triathlon race in comparison with sedentary controls.

METHODS

Twenty-two triathletes (males N = 16, females N = 6) and twenty-three controls (males N = 16, females N = 7) underwent magnetic resonance imaging (MRI) on a 3 T system at baseline (time point 1; 72 h at rest). Twelve triathletes (males N = 8, females N = 4) underwent a second scan (time point 2; 3 h of completing a triathlon race). The tensor eigenvalues (λ₁, λ₂, λ₃), mean diffusivity (MD), fractional anisotropy (FA), and T2 times were compared between controls and triathletes at time point 1 and triathletes at time points 1 and 2 using independent and paired t tests.

RESULTS

In comparison with the controls at time point 1, the T2 times of rectus femoris (RF, p < 0.02), adductor magnus (AM, p = 0.02), biceps femoris (BF, p < 0.001), semitendinosus (ST, p = 0.005), and semimembranosus (SM, p = 0.003) muscles were significantly increased in triathletes. At time point 2 in triathletes, the average tensor metrics (MD, λ₃/ λ₁) of BF, ST, and SM muscles increased (p < 0.05) and FA values in ST and SM muscles decreased (p < 0.03). T2 times were not significantly changed between both time points in triathletes.

CONCLUSION

Our results indicate that this multiparametric MRI protocol allows detection and quantification of changes in the skeletal muscle microenvironment caused by endurance training and acute strenuous exercise.

KEY POINTS

• Endurance training results in changes to the skeletal microstructure, which can be quantified using MRI-based diffusion tensor imaging. • The combined application of MRI diffusion tensor imaging and T2 mapping allows the differentiation of microstructural changes caused by active exercise or endurance training. • Environmental adaptations of the skeletal muscle caused by physical training are influenced by gender.

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.

The repeatability of bilateral diffusion tensor imaging (DTI) in the upper leg muscles of healthy adults

Objectives

Assessment of the repeatability of diffusion parameter estimations in the upper leg muscles of healthy adults over the time course of 2 weeks, from a simultaneous bilateral upper leg DTI measurement.

Methods

SE-EPI DTI datasets were acquired at 3 T in the upper legs of 15 active adults at a time interval of 2 weeks. ROIs were manually drawn for four quadriceps and three hamstring muscles of both legs. The following DTI parameters were analyzed: 1st, 2nd, and 3rd eigenvalue (λ₁, λ₂, and λ₃), mean diffusivity (MD), and fractional anisotropy (FA). DTI parameters per muscle were calculated with and without intravoxel incoherent motion (IVIM) correction together with SNR levels per muscle. Bland-Altman plots and within-subject coefficient of variation (wsCV) were calculated. Left-right differences between muscles were assessed.

Results

The Bland-Altman analysis showed good repeatability of all DTI parameters except FA for both the IVIM-corrected and standard data. wsCV values show that MD has the highest repeatability (4.5% IVIM; 5.6% standard), followed by λ₂ (4.9% IVIM; 5.5% standard), λ₁ (5.3% IVIM; 7.5% standard), and λ₃ (5.7% IVIM; 5.7% standard). wsCV values of FA were 15.2% for the IVIM-corrected data and 13.9% for the standard analysis. The SNR (41.8 ± 16.0 right leg, 41.7 ± 17.1 left leg) and wsCV values were similar for the left and right leg and no left-right bias was detected.

Conclusions

Repeatability was good for standard DTI data and slightly better for IVIM-corrected DTI data. Our protocol is suitable for DTI of the upper legs with overall good SNR.

Key Points

• The presented DTI protocol is repeatable and therefore suitable for bilateral DT imaging of the upper legs.

• Additional B1⁺calibrations improve SNR and repeatability.

• Correcting for perfusion effects improves repeatability.

Electronic supplementary material

The online version of this article (10.1007/s00330-019-06403-5) contains supplementary material, which is available to authorized users.

In vivo human lower limb muscle architecture dataset obtained using diffusion tensor imaging

'Gold standard' reference sets of human muscle architecture are based on elderly cadaveric specimens, which are unlikely to be representative of a large proportion of the human population. This is important for musculoskeletal modeling, where the muscle force-generating properties of generic models are defined by these data but may not be valid when applied to models of young, healthy individuals. Obtaining individualized muscle architecture data in vivo is difficult, however diffusion tensor magnetic resonance imaging (DTI) has recently emerged as a valid method of achieving this. DTI was used here to provide an architecture data set of 20 lower limb muscles from 10 healthy adults, including muscle fiber lengths, which are important inputs for Hill-type muscle models commonly used in musculoskeletal modeling. Maximum isometric force and muscle fiber lengths were found not to scale with subject anthropometry, suggesting that these factors may be difficult to predict using scaling or optimization algorithms. These data also highlight the high level of anatomical variation that exists between individuals in terms of lower limb muscle architecture, which supports the need of incorporating subject-specific force-generating properties into musculoskeletal models to optimize their accuracy for clinical evaluation.

Signal-to-noise ratio assessment of muscle diffusion tensor imaging using single image set and validation by the difference image method

OBJECTIVE

Signal-to-noise ratio (SNR) assessment is essential for accurate quantification of diffusion tensor imaging (DTI) metrics and usually requires the use of a difference image method using duplicate images. We aimed to estimate the SNR of DTI of thigh muscles using a single image set without duplicate images.

METHODS

DTI of one thigh were acquired on a 3 T scanner from 15 healthy adults, and scans with number of signal averages (NSA) = 4 and 8 were repeatedly acquired. SNR were evaluated for six thigh muscles. For SNR calculation from a single image set, diffusion-weighted images with similar diffusion encoding directions were grouped into pairs. The difference image of each pair was high-pass filtered in k-space to yield noise images. Noise images were also calculated with a difference method using two image sets as a reference. Subjects were divided into two groups for filter optimization and validation, respectively. The coefficient of repeatability (CR) of the SNR obtained from the two methods was also evaluated separately.

RESULTS

Bland-Altman analysis comparing the single image set method and the reference showed 95% limits of agreement of -9.2 to 9.2% for the optimization group and -12.5 to 12.6% for the validation group. The SNR measurement had a CR of 21.1% using the reference method, and 13.8% using the single image set method.

CONCLUSION

The single image method can be used for DTI SNR assessment and offers better repeatability.

ADVANCES IN KNOWLEDGE

SNR of skeletal muscle DTI can be assessed for any data set without duplicate images.

Normal values and test-retest variability of stimulated-echo diffusion tensor imaging and fat fraction measurements in the muscle

OBJECTIVES

To assess the test-retest variability of both diffusion parameters and fat fraction (FF) estimates in normal muscle, and to assess differences in normal values between muscles in the thigh.

METHODS

29 healthy volunteers (mean age 37 years, range 20-60 years, 17/29 males) completed the study. Magnetic resonance images of the mid-thigh were acquired using a stimulated echo acquisition mode-echoplanar imaging (STEAM-EPI) imaging sequence, to assess diffusion, and 2-point Dixon imaging, to assess FF. Imaging was repeated in 19 participants after a 30 min interval in order to assess test-retest variability of the measurements.

RESULTS

Intraclass correlation coefficients (ICCs) for test-retest variability were 0.99 [95% confidence interval, (CI): 0.98, 1] for FF, 0.94 (95% CI: 0.84, 0.97) for mean diffusivity and 0.89 (95% CI: 0.74, 0.96) for fractional anisotropy (FA). FF was higher in the hamstrings than the quadriceps by a mean difference of 1.81% (95% CI:1.63, 2.00)%, p < 0.001. Mean diffusivity was significantly lower in the hamstrings than the quadriceps (0.26 (0.13, 0.39) x10^-3 mm²s^-1, p < 0.001) whereas fractional anisotropy was significantly higher in the hamstrings relative to the quadriceps with a mean difference of 0.063 (0.05, 0.07), p < 0.001.

CONCLUSIONS

This study has shown excellent test-retest, variability in MR-based FF and diffusion measurements and demonstrated significant differences in these measures between hamstrings and quadriceps in the healthy thigh.

ADVANCES IN KNOWLEDGE

Test-retest variability is excellent for STEAM-EPI diffusion and 2-point Dixon-based FF measurements in the healthy muscle. Inter- and intraobserver variability were excellent for region of interest placement for STEAM-EPI diffusion and 2-point Dixon-based FF measurements in the healthy muscle. There are significant differences in FF and diffusion measurements between the hamstrings and quadriceps in the normal muscle.

The effect of high-intensity resistance exercise on lumbar musculature in patients with low back pain: a preliminary study

Background

Muscle atrophy and fatty infiltration of the lumbar extensors is associated with LBP. Exercise-based rehabilitation targets strengthening these muscles, but few studies show consistent changes in muscle quality with standard-of-care rehabilitation. The goal of this study was to assess the effect of high-intensity resistance exercise on lumbar extensor muscle size (cross sectional area) and quality (fat fraction) in individuals with low back pain (LBP).

Methods

Fourteen patients with LBP were recruited from a local rehabilitation clinic. Patients underwent MRI scanning before and after a standardized 10-week high-intensity machine-based, resistance exercise program. Patient pain, disability, anxiety/depression, satisfaction, strength, and range of motion was compared pre- and post-rehabilitation using analysis of covariance (covariates: age, gender). Exercise-induced changes in MRI, and patient functional outcome measures were correlated using Pearson’s correlation test.

Results

No significant differences were found in muscle size or fatty infiltration of the lumbar extensors over the course of rehabilitation (p > 0.31). However, patients reported reduced pain (p = 0.002) and were stronger (p = 0.03) at the conclusion of the program. Improvements in muscle size and quality for both multifidus and erector spinae correlated with improvements in disability, anxiety/depression, and strength.

Conclusion

While average muscle size and fatty infiltration levels did not change with high-intensity exercise, the results suggest that a subgroup of patients who demonstrate improvements in muscle health demonstrate the largest functional improvements. Future research is needed to identify which patients are most likely to respond to this type of treatment.

Performance of an Automated Versus a Manual Whole-Body Magnetic Resonance Imaging Workflow

OBJECTIVES

The aim of this study was to evaluate the performance of an automated workflow for whole-body magnetic resonance imaging (WB-MRI), which reduces user interaction compared with the manual WB-MRI workflow.

MATERIALS AND METHODS

This prospective study was approved by the local ethics committee. Twenty patients underwent WB-MRI for myopathy evaluation on a 3 T MRI scanner. Ten patients (7 women; age, 52 ± 13 years; body weight, 69.9 ± 13.3 kg; height, 173 ± 9.3 cm; body mass index, 23.2 ± 3.0) were examined with a prototypical automated WB-MRI workflow, which automatically segments the whole body, and 10 patients (6 women; age, 35.9 ± 12.4 years; body weight, 72 ± 21 kg; height, 169.2 ± 10.4 cm; body mass index, 24.9 ± 5.6) with a manual scan. Overall image quality (IQ; 5-point scale: 5, excellent; 1, poor) and coverage of the study volume were assessed by 2 readers for each sequence (coronal T2-weighted turbo inversion recovery magnitude [TIRM] and axial contrast-enhanced T1-weighted [ce-T1w] gradient dual-echo sequence). Interreader agreement was evaluated with intraclass correlation coefficients. Examination time, number of user interactions, and MR technicians' acceptance rating (1, highest; 10, lowest) was compared between both groups.

RESULTS

Total examination time was significantly shorter for automated WB-MRI workflow versus manual WB-MRI workflow (30.0 ± 4.2 vs 41.5 ± 3.4 minutes, P < 0.0001) with significantly shorter planning time (2.5 ± 0.8 vs 14.0 ± 7.0 minutes, P < 0.0001). Planning took 8% of the total examination time with automated versus 34% with manual WB-MRI workflow (P < 0.0001). The number of user interactions with automated WB-MRI workflow was significantly lower compared with manual WB-MRI workflow (10.2 ± 4.4 vs 48.2 ± 17.2, P < 0.0001). Planning efforts were rated significantly lower by the MR technicians for the automated WB-MRI workflow than for the manual WB-MRI workflow (2.20 ± 0.92 vs 4.80 ± 2.39, respectively; P = 0.005). Overall IQ was similar between automated and manual WB-MRI workflow (TIRM: 4.00 ± 0.94 vs 3.45 ± 1.19, P = 0.264; ce-T1w: 4.20 ± 0.88 vs 4.55 ± .55, P = 0.423). Interreader agreement for overall IQ was excellent for TIRM and ce-T1w with an intraclass correlation coefficient of 0.95 (95% confidence interval, 0.86-0.98) and 0.88 (95% confidence interval, 0.70-0.95). Incomplete coverage of the thoracic compartment in the ce-T1w sequence occurred more often in the automated WB-MRI workflow (P = 0.008) for reader 2. No other significant differences in the study volume coverage were found.

CONCLUSIONS

In conclusion, the automated WB-MRI scanner workflow showed a significant reduction of the examination time and the user interaction compared with the manual WB-MRI workflow. Image quality and the coverage of the study volume were comparable in both groups.

Determining Subject-Specific Lower-Limb Muscle Architecture Data for Musculoskeletal Models Using Diffusion Tensor Imaging

Accurate individualized muscle architecture data are crucial for generating subject-specific musculoskeletal models to investigate movement and dynamic muscle function. Diffusion tensor imaging (DTI) magnetic resonance (MR) imaging has emerged as a promising method of gathering muscle architecture data in vivo; however, its accuracy in estimating parameters such as muscle fiber lengths for creating subject-specific musculoskeletal models has not been tested. Here, we provide a validation of the method of using anatomical magnetic resonance imaging (MRI) and DTI to gather muscle architecture data in vivo by directly comparing those data obtained from MR scans of three human cadaveric lower limbs to those from dissections. DTI was used to measure fiber lengths and pennation angles, while the anatomical images were used to estimate muscle mass, which were used to calculate physiological cross-sectional area (PCSA). The same data were then obtained through dissections, where it was found that on average muscle masses and fiber lengths matched well between the two methods (4% and 1% differences, respectively), while PCSA values had slightly larger differences (6%). Overall, these results suggest that DTI is a promising technique to gather in vivo muscle architecture data, but further refinement and complementary imaging techniques may be needed to realize these goals.

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.

Paraspinal Muscle DTI Metrics Predict Muscle Strength

Background

The paraspinal muscles play an important role in the onset and progression of lower back pain. It would be of clinical interest to identify imaging biomarkers of the paraspinal musculature that are related to muscle function and strength. Diffusion tensor imaging (DTI) enables the microstructural examination of muscle tissue and its pathological changes.

Purpose

To investigate associations of DTI parameters of the lumbar paraspinal muscles with isometric strength measurements in healthy volunteers.

Study Type

Prospective.

Subjects

Twenty‐one healthy subjects (12 male, 9 female; age = 30.1 ± 5.6 years; body mass index [BMI] = 27.5 ± 2.6 kg/m²) were recruited.

Field Strength/Sequence

3 T/single‐shot echo planar imaging (ss‐EPI) DTI in 24 directions; six‐echo 3D spoiled gradient echo sequence for chemical shift encoding‐based water–fat separation.

Assessment

Paraspinal muscles at the lumbar spine were examined. Erector spinae muscles were segmented bilaterally; cross‐sectional area (CSA), proton density fat fraction (PDFF), and DTI parameters were calculated. Muscle flexion and extension maximum isometric torque values [Nm] at the back were measured with an isokinetic dynamometer and the ratio of extension to flexion strength (E/F) calculated.

Statistical Tests

Pearson correlation coefficients; multivariate regression models.

Results

Significant positive correlations were found between the ratio of extension to flexion (E/F) strength and mean diffusivity (MD) (P = 0.019), RD (P = 0.02) and the eigenvalues (λ1: P = 0.026, λ2: P = 0.033, λ3: P = 0.014). In multivariate regression models λ3 of the erector spinae muscle λ3 and gender remained statistically significant predictors of E/F (R²_adj = 0.42, P = 0.003).

Data Conclusion

DTI allowed the identification of muscle microstructure differences related to back muscle function that were not reflected by CSA and PDFF. DTI may potentially track subtle changes of back muscle tissue composition.

Level of Evidence: 3

Technical Efficacy: Stage 2

J. Magn. Reson. Imaging 2019;50:816–823.

Magnetic resonance imaging of muscle injury in elite American football players: Predictors for return to play and performance

Muscle injury accounts for about one-third of total sports-related injuries. The lower limb muscles have one of the highest predisposition for injury in high-level professional athletic sports, such as the National Football League. The commonest group of muscles injured among football players include the hamstrings, followed by the quadriceps. Muscle injuries lead to significant time, off the field and affect return to play. Sports physicians and teams have been keen on assessing such injuries and also relying on multiple tools to safely return the player back to the field. MRI plays a key role in evaluation, follow-up, and assessment for return to play (RTP). In this review, we will discuss details of muscle anatomy, incidence of muscle injuries, injury mechanisms, and use of MRI in assessment, grading, follow-up and in predicting the natural course of muscle injuries in the high-end athletic players. While the use of MRI is clear in diagnosis, and for follow up of muscle injuries, there is some limitation in its ability to predict RTP, based on current MRI classification systems. Footballers who have clinical injuries without MRI evidence of significant muscle injury (grade 0 and 1) have a shorter period of RTP. Injuries classified as high grade (3 and 4) on MRI do not correlate well with time to RTP. Further trials are required to improve the capability of MRI in its prediction of RTP.

Multicenter reproducibility study of diffusion MRI and fiber tractography of the lumbosacral nerves

BACKGROUND

Diffusion tensor imaging (DTI) has been applied in the lumbar and sacral nerves in vivo, but information about the reproducibility of this method is needed before DTI can be used reliably in clinical practice across centers.

PURPOSE

In this multicenter study the reproducibility of DTI of the lumbosacral nerves in healthy volunteers was investigated.

STUDY TYPE

Prospective control series.

SUBJECTS

Twenty healthy subjects.

FIELD STRENGTH/SEQUENCE

3T MRI. 3D turbo spin echo, and 3.0 mm isotropic DTI scan.

ASSESSMENT

The DTI scan was performed three times (twice in the same session, intrascan reproducibility, and once after an hour, interscan reproducibility). At site 2, 1 week later, the protocol was repeated (interweek reproducibility). Fiber tractography (FT) of the lumbar and sacral nerves (L3-S2) was performed to obtain values for fractional anisotropy, mean, axial, and radial diffusivity.

STATISTICAL TESTS

Reproducibility was determined using the intraclass correlation coefficient (ICC), and power calculations were performed.

RESULTS

FT was successful and reproducible in all datasets. ICCs for all diffusion parameters were high for intrascan (ranging from 0.70-0.85), intermediate for interscan (ranging from 0.61-0.73), and interweek reliability (ranging from 0.58-0.62). There were small but significant differences between the interweek diffusivity values (P < 0.0005). Depending on the effect size, nerve location, and parameter of interest, power calculations showed that sample sizes between 10 and 232 subjects are needed for cross-sectional studies.

DATA CONCLUSION

We found that DTI and FT of the lumbosacral nerves have intermediate to high reproducibility within and between scans. Based on these results, 10-58 subjects are needed to find a 10% change in parameters in cross-sectional studies of the lumbar and sacral nerves. The small significant differences of the interweek comparison suggest that results from longitudinal studies need to be interpreted carefully, since small differences may also be caused by factors other than disease progression or therapeutic effects.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:951-963.

An Efficient Modelling-Simulation-Analysis Workflow to Investigate Stump-Socket Interaction Using Patient-Specific, Three-Dimensional, Continuum-Mechanical, Finite Element Residual Limb Models

The lack of an efficient modelling-simulation-analysis workflow for creating and utilising detailed subject-specific computational models is one of the key reasons why simulation-based approaches for analysing socket-stump interaction have not yet been successfully established. Herein, we propose a novel and efficient modelling-simulation-analysis workflow that uses commercial software for generating a detailed subject-specific, three-dimensional finite element model of an entire residual limb from Diffusion Tensor MRI images in <20 min. Moreover, to complete the modelling-simulation-analysis workflow, the generated subject-specific residual limb model is used within an implicit dynamic FE simulation of bipedal stance to predict the potential sites of deep tissue injury. For this purpose, a nonlinear hyperelastic, transversely isotropic skeletal muscle constitutive law containing a deep tissue injury model was implemented in LS-DYNA. To demonstrate the feasibility of the entire modelling-simulation-analysis workflow and the fact that detailed, anatomically realistic, multi-muscle models are superior to state-of-the-art, fused-muscle models, an implicit dynamic FE analysis of 2-h bipedal stance is carried out. By analysing the potential volume of damaged muscle tissue after donning an optimally-fitted and a misfitted socket, i.e., a socket whose volume was isotropically shrunk by 10%, we were able to highlight the differences between the detailed individual- and fused-muscle models. The results of the bipedal stance simulation showed that peak stresses in the fused-muscle model were four times lower when compared to the multi-muscle model. The peak interface stress in the individual-muscle model, at the end of bipedal stance analysis, was 2.63 times lower than that in the deep tissues of the stump. At the end of the bipedal stance analysis using the misfitted socket, the fused-muscle model predicted that 7.65% of the residual limb volume was injured, while the detailed-model predicted 16.03%. The proposed approach is not only limited to modelling residual limbs but also has applications in predicting the impact of plastic surgery, for detailed forward-dynamics simulations of normal musculoskeletal systems.

High resolution isotropic diffusion imaging in post-mortem neonates: a feasibility study

OBJECTIVE:

To investigate the potential of advanced diffusion weighted imaging (DWI) in post-mortem MRI (PMMR) at 3T.

METHODS:

We acquired PMMR brain and body imaging in 12 neonates, mean gestational age 33.4 weeks (range 29-37 weeks) at 3T and 1.5T. Head and body diffusion imaging at 1.5T consisted of bipolar diffusion encoding and single-shot spin-echo echo-planar imaging (SE-EPI) for acquisition (echo time (TE) 96 ms; repetition time (TR) 2700 ms; voxel size 1.8 x 1.8 mm in-plane with slice thickness 5 mm; b-values of 500 and 1000 s/mm² applied in three orthogonal directions; total acquisition time 2:12). A whole-body 3T diffusion imaging protocol using monopolar diffusion encoding and simultaneous multislice EPI acquisition with gradients applied in 12 uniformly distributed directions was obtained (TE 53.4 ms; TR 5600 ms; 1.8 mm isotropic; multiband factor 2; b-values of 250, 750, 1250 and 1750 s/mm²; acquisition time 2:09 for a single b-value).

RESULTS:

There was significant improvement in image quality in multiband, multislice diffusion PMMR protocol. On visual assessment of image quality, 1.5T DWI scored poorly (mean 2.4 SD ± 0.47), and all 3T b-values individually scored significantly higher (p < 0.001) apart from b = 250 s/mm² which was not significantly different.

CONCLUSION:

Recent advances in diffusion sequences and hardware utilising higher field strengths and gradient performance allows whole-body diffusion PMMR imaging at high resolution with improved image quality compared to the current clinical approach.

ADVANCES IN KNOWLEDGE:

We have demonstrated feasibility of a multislice, multiband quantitative diffusion imaging sequence in the perinatal post-mortem setting. This will allow more detailed and quantitative clinical PMMR investigations using diffusion MRI in the future.

Human calf muscles changes after strength training as revealed by diffusion tensor imaging

BACKGROUND

Diffusion tensor imaging (DTI) is a non-invasive MR technique widely employed to study muscle anatomy. DTI parameters have been used to investigate microstructural changes dependent on demographic factors or transient condition such as exercise. The present study is aimed at investigating the diffusion parameters changes of the human calf muscles after a 3-months strength training protocol.

METHODS

Ten young men were trained for improving size and strength of the medial (GCM), lateral gastrocnemius (GCL) and soleus (SL) three times a week, with at least 24 hours between training sessions, for a period of three months. Diffusion weighted magnetic resonance images were acquired at the beginning of the training period (TPRE) and at three months (TPOST) using a 3T scanner. The fractional anisotropy (FA), mean diffusivity (MD) and tensor eigenvalues (λ1, λ2, λ3) were derived from the diffusion weighted imaging data.

RESULTS

We found a significant increase in λ1, λ2, λ3 and MD values and muscle volumes between TPRE and TPOST in all the examined muscles both for the left and right side. No significant differences were highlighted for FA.

CONCLUSIONS

DTI enables the investigation of muscle microstructure, allowing for the assessment of diffusion parameters variation of the muscle tissue in response to training thus being a useful tool to investigate physiological and pathological changes in skeletal muscle microstructure which could be employed to test the outcomes and the effectiveness of a given training protocol.

Diffusion tensor MRI of the healthy brachial plexus

Introduction

Diffusion Tensor MRI (DT-MRI) is a promising tool for the evaluation of brachial plexus pathology. Therefore, we introduce and evaluate a fast DT-MRI protocol (8min33s scanning with 5–10 min postprocessing time) for the brachial plexus.

Materials and methods

Thirty healthy volunteers within three age-groups (18–35, 36–55, and > 56) received DT-MRI of the brachial-plexus twice. Means of fractional-anisotropy (FA), mean-diffusivity (MD), axial-diffusivity (AD), and radial-diffusivity (RD) for the individual roots and trunks were evaluated. A stepwise forward approach was applied to test for correlations with age, sex, body-mass-index (BMI), bodysurface, height, and bodyweight. Within-subject, intra-rater, and inter-rater repeatability were assessed using Bland-Altman analysis, coefficient of variation (CV), intraclass-correlation (ICC), and minimal detectable difference (MDD).

Results

No differences between sides and root levels were found. MD, AD, and RD correlated (P < 0.05) with bodyweight. Within-subject quantification proved repeatable with CVs for FA, MD, AD, and RD of 16%, 12%, 11%, and 14%, respectively.

Discussion

The DT-MRI protocol was fast and repeatable. Found correlations should be considered in future studies of brachial plexus pathology.

Skeletal Muscle Quantitative Nuclear Magnetic Resonance Imaging and Spectroscopy as an Outcome Measure for Clinical Trials

Recent years have seen tremendous progress towards therapy of many previously incurable neuromuscular diseases. This new context has acted as a driving force for the development of novel non-invasive outcome measures. These can be organized in three main categories: functional tools, fluid biomarkers and imagery. In the latest category, nuclear magnetic resonance imaging (NMRI) offers a considerable range of possibilities for the characterization of skeletal muscle composition, function and metabolism. Nowadays, three NMR outcome measures are frequently integrated in clinical research protocols. They are: 1/ the muscle cross sectional area or volume, 2/ the percentage of intramuscular fat and 3/ the muscle water T2, which quantity muscle trophicity, chronic fatty degenerative changes and oedema (or more broadly, “disease activity”), respectively. A fourth biomarker, the contractile tissue volume is easily derived from the first two ones. The fat fraction maps most often acquired with Dixon sequences have proven their capability to detect small changes in muscle composition and have repeatedly shown superior sensitivity over standard functional evaluation. This outcome measure will more than likely be the first of the series to be validated as an endpoint by regulatory agencies. The versatility of contrast generated by NMR has opened many additional possibilities for characterization of the skeletal muscle and will result in the proposal of more NMR biomarkers. Ultra-short TE (UTE) sequences, late gadolinium enhancement and NMR elastography are being investigated as candidates to evaluate skeletal muscle interstitial fibrosis. Many options exist to measure muscle perfusion and oxygenation by NMR. Diffusion NMR as well as texture analysis algorithms could generate complementary information on muscle organization at microscopic and mesoscopic scales, respectively. ³¹P NMR spectroscopy is the reference technique to assess muscle energetics non-invasively during and after exercise. In dystrophic muscle, ³¹P NMR spectrum at rest is profoundly perturbed, and several resonances inform on cell membrane integrity. Considerable efforts are being directed towards acceleration of image acquisitions using a variety of approaches, from the extraction of fat content and water T2 maps from one single acquisition to partial matrices acquisition schemes. Spectacular decreases in examination time are expected in the near future. They will reinforce the attractiveness of NMR outcome measures and will further facilitate their integration in clinical research trials.

Improvement of Reliability of Diffusion Tensor Metrics in Thigh Skeletal Muscles

OBJECTIVE

Quantitative diffusion tensor imaging (DTI) of skeletal muscles is challenging due to the bias in DTI metrics, such as fractional anisotropy (FA) and mean diffusivity (MD), related to insufficient signal-to-noise ratio (SNR). This study compares the bias of DTI metrics in skeletal muscles via pixel-based and region-of-interest (ROI)-based analysis.

METHODS

DTI of the thigh muscles was conducted on a 3.0-T system in N = 11 volunteers using a fat-suppressed single-shot spin-echo echo planar imaging (SS SE-EPI) sequence with eight repetitions (number of signal averages (NSA) = 4 or 8 for each repeat). The SNR was calculated for different NSAs and estimated for the composite images combining all data (effective NSA = 48) as standard reference. The bias of MD and FA derived by pixel-based and ROI-based quantification were compared at different NSAs. An "intra-ROI diffusion direction dispersion angle (IRDDDA)" was calculated to assess the uniformity of diffusion within the ROI.

RESULTS

Using our standard reference image with NSA = 48, the ROI-based and pixel-based measurements agreed for FA and MD. Larger disagreements were observed for the pixel-based quantification at NSA = 4. MD was less sensitive than FA to the noise level. The IRDDDA decreased with higher NSA. At NSA = 4, ROI-based FA showed a lower average bias (0.9% vs. 37.4%) and narrower 95% limits of agreement compared to the pixel-based method.

CONCLUSION

The ROI-based estimation of FA is less prone to bias than the pixel-based estimations when SNR is low. The IRDDDA can be applied as a quantitative quality measure to assess reliability of ROI-based DTI metrics.

Weighted Mean of Signal Intensity for Unbiased Fiber Tracking of Skeletal Muscles: Development of a New Method and Comparison With Other Correction Techniques

OBJECTIVES

The aim of this study was to investigate the origin of random image artifacts in stimulated echo acquisition mode diffusion tensor imaging (STEAM-DTI), assess the role of averaging, develop an automated artifact postprocessing correction method using weighted mean of signal intensities (WMSIs), and compare it with other correction techniques.

MATERIALS AND METHODS

Institutional review board approval and written informed consent were obtained. The right calf and thigh of 10 volunteers were scanned on a 3 T magnetic resonance imaging scanner using a STEAM-DTI sequence.Artifacts (ie, signal loss) in STEAM-based DTI, presumably caused by involuntary muscle contractions, were investigated in volunteers and ex vivo (ie, human cadaver calf and turkey leg using the same DTI parameters as for the volunteers). An automated postprocessing artifact correction method based on the WMSI was developed and compared with previous approaches (ie, iteratively reweighted linear least squares and informed robust estimation of tensors by outlier rejection [iRESTORE]). Diffusion tensor imaging and fiber tracking metrics, using different averages and artifact corrections, were compared for region of interest- and mask-based analyses. One-way repeated measures analysis of variance with Greenhouse-Geisser correction and Bonferroni post hoc tests were used to evaluate differences among all tested conditions. Qualitative assessment (ie, images quality) for native and corrected images was performed using the paired t test.

RESULTS

Randomly localized and shaped artifacts affected all volunteer data sets. Artifact burden during voluntary muscle contractions increased on average from 23.1% to 77.5% but were absent ex vivo. Diffusion tensor imaging metrics (mean diffusivity, fractional anisotropy, radial diffusivity, and axial diffusivity) had a heterogeneous behavior, but in the range reported by literature. Fiber track metrics (number, length, and volume) significantly improved in both calves and thighs after artifact correction in region of interest- and mask-based analyses (P < 0.05 each). Iteratively reweighted linear least squares and iRESTORE showed equivalent results, but WMSI was faster than iRESTORE. Muscle delineation and artifact load significantly improved after correction (P < 0.05 each).

CONCLUSIONS

Weighted mean of signal intensity correction significantly improved STEAM-based quantitative DTI analyses and fiber tracking of lower-limb muscles, providing a robust tool for musculoskeletal applications.

Normalized STEAM-based diffusion tensor imaging provides a robust assessment of muscle tears in football players: preliminary results of a new approach to evaluate muscle injuries

Objectives

To assess acute muscle tears in professional football players by diffusion tensor imaging (DTI) and evaluate the impact of normalization of data.

Methods

Eight football players with acute lower limb muscle tears were examined. DTI metrics of the injured muscle and corresponding healthy contralateral muscle and of ROIs drawn in muscle tears (ROI_tear) in the corresponding healthy contralateral muscle (ROI_{hc_t}) in a healthy area ipsilateral to the injury (ROI_hi) and in a corresponding contralateral area (ROI_{hc_i}) were compared. The same comparison was performed for ratios of the injured (ROI_tear/ROI_hi) and contralateral sides (ROI_{hc_t}/ROI_{hc_i}). ANOVA, Bonferroni-corrected post-hoc and Student’s t-tests were used.

Results

Analyses of the entire muscle did not show any differences (p>0.05 each) except for axial diffusivity (AD; p=0.048). ROI_tear showed higher mean diffusivity (MD) and AD than ROI_{hc_t} (p<0.05). Fractional anisotropy (FA) was lower in ROI_tear than in ROI_hi and ROI_{hc_t} (p<0.05). Radial diffusivity (RD) was higher in ROI_tear than in any other ROI (p<0.05). Ratios revealed higher MD and RD and lower FA and reduced number and length of fibre tracts on the injured side (p<0.05 each).

Conclusions

DTI allowed a robust assessment of muscle tears in athletes especially after normalization to healthy muscle tissue.

Key Points

• STEAM-based DTI allows the investigation of muscle tears affecting professional football players.

• Fractional anisotropy and mean diffusivity differ between injured and healthy muscle areas.

• Only normalized data show differences of fibre tracking metrics in muscle tears.

• The normalization of DTI-metrics enables a more robust characterization of muscle tears.

Magnetic Resonance Neurographic and Clinical Long-Term Results After Oberlin's Transfer for Adult Brachial Plexus Injuries

The primary goal of the surgical treatment of upper brachial plexus injuries is to restore active elbow flexion. Accordingly, Oberlin's transfer has been frequently performed since 1994 and has influenced the development of other nerve transfers. However, the window of opportunity for nerve transfers remains a subject of controversy. The objective of this study was to assess magnetic resonance (MR) neurographic, clinical and electrophysiological long-term results after Oberlin's transfer. For this purpose, we performed a retrospective follow-up study. Six patients with upper brachial plexus or musculocutaneous nerve injuries were assessed; 2 were iatrogenic nerve injuries following shoulder arthroscopy or neurofibroma resection. Direct and indirect signs of neuropathy were objectified with MR neurography. Moreover, clinical and electrodiagnostic follow-up was performed and all patients completed the Disabilities of Arm, Shoulder and Hand score. Mean follow-up was 48 ± 21.9 (range, 20-73) months. Mean age was 40 ± 11.3 years and mean delay to surgery was 9 ± 3.2 months. All patients were satisfied with the functional results and the median Disabilities of Arm, Shoulder and Hand score was 21 (range, 1-57). Biceps strength was improved in 5 patients from Medical Research Council grade M0 to M4-5 and in one patient to M2-3. The donor nerve showed normal motor and sensory action potentials. Follow-up MR neurography demonstrated biceps reinnervation. Taken together, this study reports good long-term results after Oberlin's transfer. MR neurography represents an excellent, noninvasive preoperative planning tool and can be of high value in selected postoperative cases. The combined evaluation of nerves and muscles may help to indicate nerve transfers in delayed cases.

Diffusion tensor imaging in the musculoskeletal and peripheral nerve systems: from experimental to clinical applications

Magnetic resonance imaging (MRI) is a well-established imaging modality which is used in all districts of the musculoskeletal and peripheral nerve systems. More recently, initial studies have applied multiparametric MRI to evaluate quantitatively different aspects of musculoskeletal and peripheral nerve diseases, thus providing not only images but also numbers and clinical data. Besides ¹H and ³¹P magnetic resonance spectroscopy, diffusion-weighted imaging (DWI) and blood oxygenation level-dependent imaging, diffusion tensor imaging (DTI) is a relatively new MRI-based technique relying on principles of DWI, which has traditionally been used mainly for evaluating the central nervous system to track fibre course. In the musculoskeletal and peripheral nerve systems, DTI has been mostly used in experimental settings, with still few indications in clinical practice. In this review, we describe the potential use of DTI to evaluate different musculoskeletal and peripheral nerve conditions, emphasising the translational aspects of this technique from the experimental to the clinical setting.

Advanced MRI Techniques for Muscle Imaging

Advanced magnetic resonance imaging (MRI) techniques can evaluate a wide array of muscle pathologies including acute or chronic muscle injury, musculotendinous response to injury, intramuscular collections and soft tissue masses, and others. In recent years, MRI has played a more important role in muscle disease diagnosis and monitoring. MRI provides excellent spatial and contrast resolution and helps direct optimal sites for muscle biopsy. Whole-body MRI now helps identify signature patterns of muscular involvement in large anatomical regions with relative ease. Quantitative MRI has advanced the evaluation and disease tracking of muscle atrophy and fatty infiltration in entities such as muscular dystrophies. Multivoxel magnetic resonance spectroscopy (MRS) now allows a more thorough, complete evaluation of a muscle of interest without the inherent sampling bias of single-voxel MRS or biopsy. Diffusion MRI allows quantification of muscle inflammation and capillary perfusion as well as muscle fiber tracking.

Combined effect of Bacillus coagulans GBI-30, 6086 and HMB supplementation on muscle integrity and cytokine response during intense military training

The purpose of this study was to compare the coadministration of the probiotic Bacillus coagulans GBI-30, 6086 (BC30) with β-hydroxy-β-methylbutyrate (HMB) calcium (CaHMB) to CaHMB alone on inflammatory response and muscle integrity during 40 days of intense military training. Soldiers were randomly assigned to one of two groups: CaHMB with BC30 (CaHMBBC30; n = 9) or CaHMB with placebo (CaHMBPL, n = 9). A third group of participants served as a control (CTL; n = 8). During the first 28 days soldiers were garrisoned on base and participated in the same training tasks. During the final 2 wk soldiers navigated 25–30 km per night in difficult terrain carrying ~35 kg of equipment. All assessments (blood draws and diffusion tensor imaging to assess muscle integrity) were conducted before and ~12 h after final supplement consumption. Analysis of covariance was used to analyze all blood and muscle measures. Significant attenuations were noted in IL-1β, IL-2, IL-6, CX3CL1, and TNF-α for both CaHMBBC30 and CaHMBPL compared with CTL. Plasma IL-10 concentrations were significantly attenuated for CaHMBBC30 compared with CTL only. A significant decrease in apparent diffusion coefficients was also observed for CaHMBBC30 compared with CaHMBPL. Results provide further evidence that HMB supplementation may attenuate the inflammatory response to intense training and that the combination of the probiotic BC30 with CaHMB may be more beneficial than CaHMB alone in maintaining muscle integrity during intense military training.

NEW & NOTEWORTHY β-Hydroxy-β-methylbutyrate (HMB) in its free acid form was reported to attenuate inflammation and maintain muscle integrity during military training. However, this formulation was difficult to maintain in the field. In this investigation, soldiers ingested HMB calcium (CaHMB) with Bacillus coagulans (BC30) or CaHMB alone during 40 days of training. Results indicated that CaHMB attenuated the inflammatory response and that BC30 combined with CaHMB may be more beneficial than CaHMB alone in maintaining muscle integrity during intense military training.

Intravoxel incoherent motion modeling in the kidneys: Comparison of mono-, bi-, and triexponential fit

PURPOSE

To evaluate if a three-component model correctly describes the diffusion signal in the kidney and whether it can provide complementary anatomical or physiological information about the underlying tissue.

MATERIALS AND METHODS

Ten healthy volunteers were examined at 3T, with T2 -weighted imaging, diffusion tensor imaging (DTI), and intravoxel incoherent motion (IVIM). Diffusion tensor parameters (mean diffusivity [MD] and fractional anisotropy [FA]) were obtained by iterative weighted linear least squares fitting of the DTI data and mono-, bi-, and triexponential fit parameters (D1 , D2 , D3 , ffast2 , ffast3 , and finterm ) using a nonlinear fit of the IVIM data. Average parameters were calculated for three regions of interest (ROIs) (cortex, medulla, and rest) and from fiber tractography. Goodness of fit was assessed with adjusted R2 ( Radj2) and the Shapiro-Wilk test was used to test residuals for normality. Maps of diffusion parameters were also visually compared.

RESULTS

Fitting the diffusion signal was feasible for all models. The three-component model was best able to describe fast signal decay at low b values (b < 50), which was most apparent in Radj2 of the ROI containing high diffusion signals (ROIrest ), which was 0.42 ± 0.14, 0.61 ± 0.11, 0.77 ± 0.09, and 0.81 ± 0.08 for DTI, one-, two-, and three-component models, respectively, and in visual comparison of the fitted and measured S0 . None of the models showed significant differences (P > 0.05) between the diffusion constant of the medulla and cortex, whereas the ffast component of the two and three-component models were significantly different (P < 0.001).

CONCLUSION

Triexponential fitting is feasible for the diffusion signal in the kidney, and provides additional information.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:228-239.

Imaging of Muscle Injuries in Sports Medicine: Sports Imaging Series

In sports-related muscle injuries, the main goal of the sports medicine physician is to return the athlete to competition-balanced against the need to prevent the injury from worsening or recurring. Prognosis based on the available clinical and imaging information is crucial. Imaging is crucial to confirm and assess the extent of sports-related muscle injuries and may help to guide management, which directly affects the prognosis. This is especially important when the diagnosis or grade of injury is unclear, when recovery is taking longer than expected, and when interventional or surgical management may be necessary. Several imaging techniques are widely available, with ultrasonography and magnetic resonance imaging currently the most frequently applied in sports medicine. This state of the art review will discuss the main imaging modalities for the assessment of sports-related muscle injuries, including advanced imaging techniques, with the focus on the clinical relevance of imaging features of muscle injuries. ^© RSNA, 2017 Online supplemental material is available for this article.

Significance of Diffusion Tensor Imaging of Vastus Medialis Oblique in Recurrent Patellar Dislocation

Background:

Numerous studies have investigated the influence of osseous factors on patellofemoral joint instability, but research on the influence of dynamic muscle factors in vivo is still in the exploratory stage. This study aimed to use magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) to evaluate vastus medialis oblique (VMO) fiber bundles in patients with recurrent patellar dislocation to explore the changes in muscle morphology and function.

Methods:

This prospective study involved 30 patients (7 males and 23 females; average age, 21.4 ± 3.8 years) clinically diagnosed with recurrent patellar dislocation in Peking University Third Hospital and 30 healthy volunteers matched for age, sex, and body mass index in our medical school between January 2014 and October 2014. None of the patients had a recent history of traumatic patellar dislocation or transient patellar dislocation. All patients underwent conventional MRI and DTI of the knee. The cross-sectional area of the VMO on MRI and the fractional anisotropy (FA), apparent diffusion coefficient (ADC), and primary (λ1), secondary (λ2), and three-level characteristic (λ3) values on DTI were measured. The independent-samples t-test was used to compare these parameters between the two groups.

Results:

Compared with the control group, the patient group showed significantly higher FA values (0.39 ± 0.05 vs. 0.33 ± 0.03) and significantly lower ADC (1.51 ± 0.13 vs. 1.58 ± 0.07), λ2 (4.96 ± 0.13 vs. 5.04 ± 0.07), and λ3 values (4.44 ± 0.14 vs. 4.58 ± 0.07; t = 5.99, t = –2.58, t = –3.02, and t = –4.88, respectively; all P < 0.05). Cross-sectional VMO area and λ1 values did not differ between the two groups (t = –1.82 and t = 0.22, respectively; both P > 0.05).

Conclusions:

The functional status of the VMO is closely associated with recurrent patellar dislocation. MRI, especially DTI (FA, ADC, λ2, and λ3), can detect early changes in VMO function and might facilitate the noninvasive monitoring of the functional status of the VMO in patients with recurrent patellar dislocation.

* A 3D Tissue-Printing Approach for Validation of Diffusion Tensor Imaging in Skeletal Muscle

The ability to noninvasively assess skeletal muscle microstructure, which predicts function and disease, would be of significant clinical value. One method that holds this promise is diffusion tensor magnetic resonance imaging (DT-MRI), which is sensitive to the microscopic diffusion of water within tissues and has become ubiquitous in neuroimaging as a way of assessing neuronal structure and damage. However, its application to the assessment of changes in muscle microstructure associated with injury, pathology, or age remains poorly defined, because it is difficult to precisely control muscle microstructural features in vivo. However, recent advances in additive manufacturing technologies allow precision-engineered diffusion phantoms with histology informed skeletal muscle geometry to be manufactured. Therefore, the goal of this study was to develop skeletal muscle phantoms at relevant size scales to relate microstructural features to MRI-based diffusion measurements. A digital light projection based rapid 3D printing method was used to fabricate polyethylene glycol diacrylate based diffusion phantoms with (1) idealized muscle geometry (no geometry; fiber sizes of 30, 50, or 70 μm or fiber size of 50 μm with 40% of walls randomly deleted) or (2) histology-based geometry (normal and after 30-days of denervation) containing 20% or 50% phosphate-buffered saline (PBS). Mean absolute percent error (8%) of the printed phantoms indicated high conformity to templates when "fibers" were >50 μm. A multiple spin-echo echo planar imaging diffusion sequence, capable of acquiring diffusion weighted data at several echo times, was used in an attempt to combine relaxometry and diffusion techniques with the goal of separating intracellular and extracellular diffusion signals. When fiber size increased (30-70 μm) in the 20% PBS phantom, fractional anisotropy (FA) decreased (0.32-0.26) and mean diffusivity (MD) increased (0.44 × 10^-3 mm²/s-0.70 × 10^-3 mm²/s). Similarly, when fiber size increased from 30 to 70 μm in the 50% PBS diffusion phantoms, a small change in FA was observed (0.18-0.22), but MD increased from 0.86 × 10^-3 mm²/s to 1.79 × 10^-3 mm²/s. This study demonstrates a novel application of tissue engineering to understand complex diffusion signals in skeletal muscle. Through this work, we have also demonstrated the feasibility of 3D printing for skeletal muscle with relevant matrix geometries and physiologically relevant tissue characteristics.

Skeletal muscle diffusion tensor-MRI fiber tracking: rationale, data acquisition and analysis methods, applications and future directions

The mechanical functions of muscles involve the generation of force and the actuation of movement by shortening or lengthening under load. These functions are influenced, in part, by the internal arrangement of muscle fibers with respect to the muscle's mechanical line of action. This property is known as muscle architecture. In this review, we describe the use of diffusion tensor (DT)-MRI muscle fiber tracking for the study of muscle architecture. In the first section, the importance of skeletal muscle architecture to function is discussed. In addition, traditional and complementary methods for the assessment of muscle architecture (brightness-mode ultrasound imaging and cadaver analysis) are presented. Next, DT-MRI is introduced and the structural basis for the reduced and anisotropic diffusion of water in muscle is discussed. The third section discusses issues related to the acquisition of skeletal muscle DT-MRI data and presents recommendations for optimal strategies. The fourth section discusses methods for the pre-processing of DT-MRI data, the available approaches for the calculation of the diffusion tensor and the seeding and propagating of fiber tracts, and the analysis of the tracking results to measure structural properties pertinent to muscle biomechanics. Lastly, examples are presented of how DT-MRI fiber tracking has been used to provide new insights into how muscles function, and important future research directions are highlighted. Copyright © 2016 John Wiley & Sons, Ltd.

Dynamic DTI (dDTI) shows differing temporal activation patterns in post-exercise skeletal muscles

OBJECT

To assess post-exercise recovery of human calf muscles using dynamic diffusion tensor imaging (dDTI).

MATERIALS AND METHODS

DTI data (6 directions, b = 0 and 400 s/mm²) were acquired every 35 s from seven healthy men using a 3T MRI, prior to (4 volumes) and immediately following exercise (13 volumes, ~7.5 min). Exercise consisted of 5-min in-bore repetitive dorsiflexion-eversion foot motion with 0.78 kg resistance. Diffusion tensors calculated at each time point produced maps of mean diffusivity (MD), fractional anisotropy (FA), radial diffusivity (RD), and signal at b = 0 s/mm² (S₀). Region-of-interest (ROI) analysis was performed on five calf muscles: tibialis anterior (ATIB), extensor digitorum longus (EDL) peroneus longus (PER), soleus (SOL), and lateral gastrocnemius (LG).

RESULTS

Active muscles (ATIB, EDL, PER) showed significantly elevated initial MD post-exercise, while predicted inactive muscles (SOL, LG) did not (p < 0.0001). The EDL showed a greater initial increase in MD (1.90 × 10^-4mm²/s) than ATIB (1.03 × 10^-4mm²/s) or PER (8.79 × 10^-5 mm²/s) (p = 7.40 × 10^-4), and remained significantly elevated across more time points than ATIB or PER. Significant increases were observed in post-exercise EDL S₀ relative to other muscles across the majority of time points (p < 0.01 to p < 0.001).

CONCLUSIONS

dDTI can be used to differentiate exercise-induced changes between muscles. These differences are suggested to be related to differences in fiber composition.

Effects of perfusion on DTI and DKI estimates in the skeletal muscle

PURPOSE

In this study, we evaluated the effects of perfusion of the skeletal muscle on diffusion tensor imaging (DTI) and diffusional kurtosis imaging (DKI) parameters and their reproducibility.

METHODS

Diffusion tensor imaging and DKI models, with and without intravoxel incoherent motion (IVIM) correction, were applied to simulated data at different physiological conditions and signal-to-noise ratio levels. Next, the same models were applied to data of the right calf of five healthy volunteers, acquired twice at 3 telsa. For six muscles, we evaluated the correlation of the perfusion signal fraction, with parameters derived from DTI and DKI, and performed repeatability analysis with and without IVIM correction. Additionally, the IVIM correction was compared to a multishell acquisition approach that minimizes perfusion effects on DTI estimates.

RESULTS

Simulations and acquired data showed that DTI and DKI estimates were biased proportionally to the perfusion signal fraction, and that IVIM correction was needed for accurate estimation of the DTI and DKI parameters. However, taking perfusion into account did not improve repeatability.

CONCLUSION

Blood perfusion has an effect on DTI and DKI estimations, but it can be minimized with IVIM correction or multishell acquisition strategies. Magn Reson Med 78:233-246, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Hamstring Reinjuries Occur at the Same Location and Early After Return to Sport: A Descriptive Study of MRI-Confirmed Reinjuries

BACKGROUND

Despite relatively high reinjury rates after acute hamstring injuries, there is a lack of detailed knowledge about where and when hamstring reinjuries occur, and studies including imaging-confirmed reinjuries are scarce.

PURPOSE

To investigate the location, radiological severity, and timing of reinjuries on magnetic resonance imaging (MRI) compared with the index injury.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A MRI scan was obtained ≤5 days after an acute hamstring index injury in 180 athletes, and time to return to sport (RTS) was registered. Athletes with an MRI-confirmed reinjury in the same leg ≤365 days after RTS were included. Categorical grading and standardized MRI parameters of the index injury and reinjury were scored by a single radiologist (with excellent intraobserver reliability). To determine the location of the reinjury, axial and coronal views of the index injury and reinjury were directly compared on proton density-weighted fat-suppressed images.

RESULTS

In the 19 athletes included with reinjury, 79% of these reinjuries occurred in the same location within the muscle as the index injury. The median time to RTS after the index injury was 19 days (range, 5-37 days; interquartile range [IQR], 15 days). The median time between the index injury and reinjury was 60 days (range, 20-316 days; IQR, 131 days) and the median time between RTS after the index injury and the reinjury was 24 days (range, 4-311 days; IQR, 140 days). More than 50% of reinjuries occurred within 25 days (4 weeks) after RTS from the index injury and 50% occurred within 50 days after the index injury. All reinjuries with more severe radiological grading occurred in the same location as the index injury.

CONCLUSION

The majority of the hamstring reinjuries occurred in the same location as the index injury, early after RTS and with a radiologically greater extent, suggesting incomplete biological and/or functional healing of the index injury. Specific exercise programs focusing on reinjury prevention initiated after RTS from the index injury are highly recommended.

Diffusional kurtosis MRI of the lower leg: changes caused by passive muscle elongation and shortening

Diffusional kurtosis MRI (DKI) quantifies the deviation of water diffusion from a Gaussian distribution. We investigated the influence of passive elongation and shortening of the lower leg muscles on the DKI parameters D (diffusion coefficient) and K (kurtosis). After approval by the local ethics committee, eight healthy volunteers (age, 29.1 ± 2.9 years) underwent MRI of the lower leg at 3 T. Diffusion-weighted images were acquired with 10 different b values at three ankle positions (passive dorsiflexion 10°, neutral position 0°, passive plantar flexion 40°). Parametrical maps of D and K were obtained by voxel-wise fitting of the signal intensities using a non-linear Levenberg-Marquardt algorithm. D and K were measured in the tibialis anterior, medial and lateral gastrocnemius, and soleus muscles. In the neutral position, D and K values were in the range between 1.66-1.79 × 10(-3) mm(2) /s and 0.21-0.39, respectively. D and K increased with passive shortening, and decreased with passive elongation, which could also be illustrated on the parametrical maps. In dorsiflexion, D (p < 0.01) and K (p = 0.036) were higher in the tibialis anterior than in the medial gastrocnemius. In plantar flexion, the opposite was found for K (p = 0.035). DKI parameters in the lower leg muscles are significantly influenced by the ankle joint position, indicating that the diffusion of water molecules in skeletal muscle deviates from a Gaussian distribution depending on muscle tonus. Copyright © 2016 John Wiley & Sons, Ltd.

[Chronic sports injuries of the knee joint]

Chronic sports injuries of the knee joint are common and mainly caused by repetitive (micro) trauma and exertion. Chronic insertion tendinopathies and avulsion fractures and symptoms related to entrapment, friction and impingement can be pathophysiologically distinguished in athletes. In this review, we depict the characteristic magnetic resonance imaging (MRI) findings of the most commonly occurring pathologies.

MR imaging of skeletal muscle signal alterations: Systematic approach to evaluation

Muscle edema or edema-like signal alterations are commonly encountered findings in musculoskeletal magnetic resonance (MR) imaging. Although such signal alterations are very sensitive for detection of the underlying muscle pathology, these are often non-specific findings. Encompassing knowledge of their typical clinical presentations, characteristic appearances and patterns of muscle signal alterations and following a systematic approach towards their assessment, a reader can effectively narrow down the differential diagnosis. This article outlines the role of conventional imaging and advanced anatomic and functional musculoskeletal MR imaging techniques in the evaluation of various muscle disorders and presents a systematic approach towards their diagnosis and management.