MRI analysis of structural changes in skeletal muscles and surrounding tissues following long-term walking exercise with training equipment

In vivo electrical conductivity measurement of muscle, cartilage, and peripheral nerve around knee joint using MR-electrical properties tomography

This study aimed to investigate whether in vivo MR-electrical properties tomography (MR-EPT) is feasible in musculoskeletal tissues by evaluating the conductivity of muscle, cartilage, and peripheral nerve around the knee joint, and to explore whether these measurements change after exercise. This prospective study was approved by the institutional review board. On February 2020, ten healthy volunteers provided written informed consent and underwent MRI of the right knee using a three-dimensional balanced steady-state free precession (bSSFP) sequence. To test the effect of loading, the subjects performed 60 squatting exercises after baseline MRI, immediately followed by post-exercise MRI with the same sequences. After reconstruction of conductivity map based on the bSSFP sequence, conductivity of muscles, cartilages, and nerves were measured. Measurements between the baseline and post-exercise MRI were compared using the paired t-test. Test–retest reliability for baseline conductivity was evaluated using the intraclass correlation coefficient. The baseline and post-exercise conductivity values (mean ± standard deviation) [S/m] of muscles, cartilages, and nerves were 1.73 ± 0.40 and 1.82 ± 0.50 (p = 0.048), 2.29 ± 0.47 and 2.51 ± 0.37 (p = 0.006), and 2.35 ± 0.57 and 2.36 ± 0.57 (p = 0.927), respectively. Intraclass correlation coefficient for the baseline conductivity of muscles, cartilages, and nerves were 0.89, 0.67, and 0.89, respectively. In conclusion, in vivo conductivity measurement of musculoskeletal tissues is feasible using MR-EPT. Conductivity of muscles and cartilages significantly changed with an overall increase after exercise.

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.

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.

Reduced Lower-Limb Muscle Strength and Volume in Patients With Type 2 Diabetes in Relation to Neuropathy, Intramuscular Fat, and Vitamin D Levels

OBJECTIVE

Muscle weakness and atrophy of the lower limbs may develop in patients with diabetes, increasing their risk of falls. The underlying basis of these abnormalities has not been fully explained. The aim of this study was to objectively quantify muscle strength and size in patients with type 2 diabetes mellitus (T2DM) in relation to the severity of neuropathy, intramuscular noncontractile tissue (IMNCT), and vitamin D deficiency.

RESEARCH DESIGN AND METHODS

Twenty patients with T2DM and 20 healthy control subjects were matched by age, sex, and BMI. Strength and size of knee extensor, flexor, and ankle plantar and dorsiflexor muscles were assessed in relation to the severity of diabetic sensorimotor polyneuropathy (DSPN), amount of IMNCT, and serum 25-hydroxyvitamin D (25OHD) levels.

RESULTS

Compared with control subjects, patients with T2DM had significantly reduced knee extensor strength (P = 0.003) and reduced muscle volume of both knee extensors (P = 0.045) and flexors (P = 0.019). Ankle plantar flexor strength was also significantly reduced (P = 0.001) but without a reduction in ankle plantar flexor (P = 0.23) and dorsiflexor (P = 0.45) muscle volumes. IMNCT was significantly increased in the ankle plantar (P = 0.006) and dorsiflexors (P = 0.005). Patients with DSPN had significantly less knee extensor strength than those without (P = 0.02) but showed no difference in knee extensor volume (P = 0.38) and ankle plantar flexor strength (P = 0.21) or volume (P = 0.96). In patients with <25 nmol/L versus >25 nmol/L 25OHD, no significant differences were found for knee extensor strength and volume (P = 0.32 vs. 0.18) and ankle plantar flexors (P = 0.58 vs. 0.12).

CONCLUSIONS

Patients with T2DM have a significant reduction in proximal and distal leg muscle strength and a proximal but not distal reduction in muscle volume possibly due to greater intramuscular fat accumulation in distal muscles. Proximal but not distal muscle strength is related to the severity of peripheral neuropathy but not IMNCT or 25OHD level.

Techniques and applications of skeletal muscle diffusion tensor imaging: A review

Diffusion tensor imaging (DTI) is increasingly applied to study skeletal muscle physiology, anatomy, and pathology. The reason for this growing interest is that DTI offers unique, noninvasive, and potentially diagnostically relevant imaging readouts of skeletal muscle structure that are difficult or impossible to obtain otherwise. DTI has been shown to be feasible within most skeletal muscles. DTI parameters are highly sensitive to patient-specific properties such as age, body mass index (BMI), and gender, but also to more transient factors such as exercise, rest, pressure, temperature, and relative joint position. However, when designing a DTI study one should not only be aware of sensitivity to the above-mentioned factors but also the fact that the DTI parameters are dependent on several acquisition parameters such as echo time, b-value, and diffusion mixing time. The purpose of this review is to provide an overview of DTI studies covering the technical, demographic, and clinical aspects of DTI in skeletal muscles. First we will focus on the critical aspects of the acquisition protocol. Second, we will cover the reported normal variance in skeletal muscle diffusion parameters, and finally we provide an overview of clinical studies and reported parameter changes due to several (patho-)physiological conditions.

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

PURPOSE

To develop a protocol for diffusion-tensor imaging (DTI) of the complete upper legs and to demonstrate feasibility of detection of subclinical sports-related muscle changes in athletes after strenuous exercise, which remain undetected by using conventional T2-weighted magnetic resonance (MR) imaging with fat suppression.

MATERIALS AND METHODS

The research was approved by the institutional ethics committee review board, and the volunteers provided written consent before the study. Five male amateur long-distance runners underwent an MR examination (DTI, T1-weighted MR imaging, and T2-weighted MR imaging with fat suppression) of both upper legs 1 week before, 2 days after, and 3 weeks after they participated in a marathon. The tensor eigenvalues (λ1, λ2, and λ3), the mean diffusivity, and the fractional anisotropy (FA) were derived from the DTI data. Data per muscle from the three time-points were compared by using a two-way mixed-design analysis of variance with a Bonferroni posthoc test.

RESULTS

The DTI protocol allowed imaging of both complete upper legs with adequate signal-to-noise ratio and within a 20-minute imaging time. After the marathon, T2-weighted MR imaging revealed grade 1 muscle strains in nine of the 180 investigated muscles. The three eigenvalues, mean diffusivity, and FA were significantly increased (P < .05) in the biceps femoris muscle 2 days after running. Mean diffusivity and eigenvalues λ1 and λ2 were significantly (P < .05) increased in the semitendinosus and gracilis muscles 2 days after the marathon.

CONCLUSION

A feasible method for DTI measurements of the upper legs was developed that fully included frequently injured muscles, such as hamstrings, in one single imaging session. This study also revealed changes in DTI parameters that over time were not revealed by qualitative T2-weighted MR imaging with fat suppression.

Changes in diffusion tensor imaging (DTI) eigenvalues of skeletal muscle due to hybrid exercise training

Several studies have proposed the cell membrane as the main water diffusion restricting factor in the skeletal muscle cell. We sought to establish whether a particular form of exercise training (which is likely to affect only intracellular components) could affect water diffusion. The purpose of this study is to characterise prospectively the changes in diffusion tensor imaging (DTI) eigenvalues of thigh muscle resulting from hybrid training (HYBT) in patients with non-alcoholic fatty liver disease (NAFLD). Twenty-one NAFLD patients underwent HYBT for 30 minutes per day, twice a week for 6 months. Patients were scanned using DTI of the thigh pre- and post-HYBT. Fractional anisotropy (FA), apparent diffusion coefficient (ADC), the three eigenvalues lambda 1 (λ1), λ2, λ3, and the maximal cross sectional area (CSA) were measured in bilateral thigh muscles: knee flexors (biceps femoris (BF), semitendinosus (ST), semimembranous (SM)) and knee extensors (medial vastus (MV), intermediate vastus (IV), lateral vastus (LV), and rectus femoris (RF)), and compared pre- and post-HYBT by paired t-test. Muscle strength of extensors (P<0.01), but not flexors, increased significantly post-HYBT. For FA, ADC and eigenvalues, the overall picture was of increase. Some (P<0.05 in λ2 and P<0.01 in λ1) eigenvalues of flexors and all (λ1-λ3) eigenvalues of extensors increased significantly (P<0.01) post-HYBT. HYBT increased all 3 eigenvalues. We suggest this might be caused by enlargement of muscle intracellular space.

Detection of exercise load-associated differences in hip muscles by texture analysis

We examined whether specific physical exercise loading is associated with texture parameters from hip muscles scanned with magnetic resonance imaging (MRI). Ninety-one female athletes representing five distinct exercise-loading groups (high-impact, odd-impact, low-impact, nonimpact and high-magnitude) and 20 nonathletic female controls underwent MRI of the hip. Texture parameters were computed from the MRI images of four hip muscles (gluteus maximus, gluteus medius, iliopsoas and obturator internus). Differences in muscle texture between the athlete groups and the controls were evaluated using Mann-Whitney U-test. Significant (P < 0.05) textural differences were found between the high-impact (triple and high jumpers) and the control group in gluteus medius, iliopsoas and obturator internus muscles. Texture of the gluteus maximus, gluteus medius and obturator internus muscles differed significantly between the odd impact (soccer and squash players) and the control group. Textures of all studied muscles differed significantly between the low impact (endurance runners) and the controls. Only the gluteus medius muscle differed significantly between the nonimpact (swimmers) and the controls. No significant difference in muscle texture was found between the high-magnitude (powerlifters) and the control group. In conclusion, MRI texture analysis provides a quantitative method capable of detecting textural differences in hip muscles that are associated with specific types of long-term exercise loadings.

DTI of human skeletal muscle: the effects of diffusion encoding parameters, signal-to-noise ratio and T2 on tensor indices and fiber tracts

In this study, we have performed simulations to address the effects of diffusion encoding parameters, signal-to-noise ratio (SNR) and T2 on skeletal muscle diffusion tensor indices and fiber tracts. Where appropriate, simulations were corroborated and validated by in vivo diffusion tensor imaging (DTI) of human skeletal muscle. Specifically, we have addressed: (i) the accuracy and precision of the diffusion parameters and eigenvectors at different SNR levels; (ii) the effects of the diffusion gradient direction encoding scheme; (iii) the optimal b value for diffusion tensor estimation; (iv) the effects of changes in skeletal muscle T2; and, finally, the influence of SNR on fiber tractography and derived (v) fiber lengths, (vi) pennation angles and (vii) fiber curvatures. We conclude that accurate DTI of skeletal muscle requires an SNR of at least 25, a b value of between 400 and 500 s/mm(2), and data acquired with at least 12 diffusion gradient directions homogeneously distributed on half a sphere. Furthermore, for DTI studies focusing on skeletal muscle injury or pathology, apparent changes in the diffusion parameters need to be interpreted with great care in view of the confounding effects of T2, particularly for moderate to low SNR values.

Age- and stroke-related skeletal muscle changes: a review for the geriatric clinician

Independently, aging and stroke each have a significant negative impact on skeletal muscle, but the potential cumulative effects of aging and stroke have not been explored. Optimal interventions for individuals post stroke may include those that specifically target skeletal muscle. Addressing changes in muscles may minimize activity limitations and enhance participation post stroke. This article reviews the impact of aging and stroke on muscle morphology and composition, including fiber atrophy, reductions in muscle cross-sectional area, changes in muscle fiber distributions, and increases in intramuscular fat. Relationships between changes in muscle structure, muscle function, and physical mobility are reviewed. Clinical recommendations that preserve and enhance skeletal muscle in the aging adult and individuals post stroke are discussed. Future research directions that include systematic comparison of the differences in skeletal muscle between younger and older adults who have sustained a stroke are suggested.

Alterations in intramuscular water movement associated with mechanical changes in human skeletal muscle fibers: an evaluation using magnetic resonance diffusion-weighted imaging and B-mode ultrasonography

BACKGROUND

Intramuscular water movement is expected to be affected by the mechanical changes of the muscle fibers. However, the effect of changes in fiber length (FL) and pennation angle (PA) on the water movement has not been sufficiently investigated in human skeletal muscles.

PURPOSE

To determine the relationship between intramuscular water movement and the mechanical changes in human muscle fibers.

MATERIAL AND METHODS

Axial magnetic resonance diffusion-weighted images of the right leg (eight men) were taken using a 1.5-Tesla device with the ankle joint maximally dorsiflexed and maximally plantar flexed. The apparent diffusion coefficient (ADC) values of both the dorsiflexors (the superficial and deep parts of the tibialis anterior) and the plantar flexors (medial gastrocnemius and soleus) were calculated along three orthogonal axes (S-I: superior-to-inferior, A-P: anterior-to-posterior, and R-L: right-to-left). FL and PA of both muscle groups were also calculated from longitudinal B-mode ultrasound images with the ankle joint maximally dorsiflexed and plantar flexed.

RESULTS

There was a significant increase in the ADC in superficial (P < 0.05) and deep (P < 0.05) parts of the dorsiflexors in the S-I direction when the ankle was plantar flexed and in the A-P and R-L directions when the ankle was dorsiflexed (P < 0.05). The plantar flexors showed significantly elevated ADC in the S-I direction when the ankle was dorsiflexed (P < 0.05), and in the A-P and R-L directions when the ankle was plantar flexed (P < 0.05). The dorsiflexors also showed significantly increased PA and decreased FL values when the ankle was dorsiflexed (P < 0.05). The plantar flexors displayed similar morphological changes when the ankle was plantar flexed (P < 0.05).

CONCLUSION

Water diffusion is affected by structural changes in the long axis of the muscle fibers, namely the changes in PA and FL.

Appropriate slice location to assess maximal cross-sectional area of individual rotator cuff muscles in normal adults and athletes

PURPOSE

We investigated appropriate slice locations for magnetic resonance (MR) imaging evaluation of the maximal cross-sectional area (CSA) of individual rotator cuff (RC) muscles in normal adults and athletes.

METHODS

We used a 1.5-tesla MR system with body-array and spine coils to obtain oblique sagittal T(1)-weighted shoulder images of 29 normal adults (16 men, 13 women); 6 national-level competitive swimmers (4 men, 2 women); 10 collegiate-level female badminton players; and 7 collegiate-level male rowers. We calculated the supraspinatus, infraspinatus, teres minor, and subscapularis CSAs at the 0-1 locations on the scapula (dividing scapula width into 11 locations), 0 representing the medial border of the scapula and 1, the glenoid fossa surface. We evaluated the differences in CSAs at relative locations on the scapula for each muscle in normal adults, swimmers, badminton players, and rowers using a one-way analysis of variance followed by the Tukey test (P<0.05).

RESULTS

The supraspinatus CSAs were maximal at 0.7 for all groups. The infraspinatus CSAs were maximal at 0.5 for normal men and women and badminton players, 0.4- and 0.5 locations for swimmers, and 0.4 for rowers. The teres minor CSAs were maximal at 0.9 for all groups except the swimmers (1 location). The subscapularis CSAs were maximal at 0.7 in men, swimmers, and badminton players and 0.6 in women and rowers.

CONCLUSION

The appropriate slice locations for evaluating maximal CSAs are slightly lateral to the center of the scapula for the supraspinatus and subscapularis, at approximately the center of the scapula for the infraspinatus, and near the glenoid fossa for the teres minor. These slice locations should be clinically useful for morphological and/or function-related assessments of shoulder RC muscles.

Simultaneous temperature and regional blood volume measurements in human muscle using an MRI fast diffusion technique

The thermal dependence of the translational diffusion coefficient and of the regional blood volume was investigated in vivo by using a special MR pulsed gradient technique with reduced sensitivity to bulk tissue motion. Measurements were done at 0.5 T, using a small gradient insert. The diffusion coefficient of muscle water was calibrated against thermocouple-measured temperature in vitro, both with the muscle fibers parallel and perpendicular to the diffusion gradient. The maximum muscle temperature variation obtained by percutaneous conduction was -8.8 +/- 1.6 degrees C under cooling and +3.7 +/- 1.6 degrees C under heating, from basal state. Simultaneously the fractional regional blood volume decreased by a factor of 3.5 under cooling and increased by a factor of 2.7 under heating. Due to the interdependence of microcirculation and tissue temperature, this technique may be used to follow heat production or deposition in living tissue (muscle exercise, electromagnetic irradiation, etc.).