Structure and function of Achilles and patellar tendons following moderate slow resistance training in young and old men.

The aim of this study was to investigate the effect of aging and resistance training with a moderate load on the size and mechanical properties of the patellar (PT) and Achilles tendon (AT) and their associated aponeuroses; medial gastrocnemius (MG) and vastus lateralis (VL). Young (Y55; 24.8 ± 3.8 yrs, n = 11) and old men (O55; 70.0 ± 4.6 yrs, n = 13) were assigned to undergo a training program (12 weeks; 3 times/week) of moderate slow resistance training [55% of one repetition maximum (RM)] of the triceps surae and quadriceps muscles. Tendon dimensions were assessed using 1.5 T magnetic resonance imaging before and after 12 weeks. AT and PT cross sectional area (CSA) were determined every 10% of tendon length. Mechanical properties of the free AT, MG aponeurosis, PT, and VL aponeurosis were assessed using ultrasonography (deformation) and tendon force measurements. CSA of the AT but not PT was greater in O55 compared with Y55. At baseline, mechanical properties were generally lower in O55 than Y55 for AT, MG aponeurosis and VL aponeurosis (Young's modulus) but not for PT. CSA of the AT and PT increased equally in both groups following training. Further, for a given force, stiffness and Young's modulus also increased equally for VL aponeurosis and AT, for boths groups. The present study highlights that except for the PT, older men have lower tendon (AT, MG aponeurosis, and VL aponeurosis) mechanical properties than young men and 12-weeks of moderate slow resistance training appears sufficient to improve tendon size and mechanical adaptations in both young and older men. New and Noteworthy: These novel findings suggest that short-term moderate slow resistance training induces equal improvements in tendon size and mechanics regardless of age.

Improved Ultrasound Attenuation Measurement Method for the Non-invasive Evaluation of Hepatic Steatosis Using FibroScan.

Controlled attenuation parameter (CAP) is a measurement of ultrasound attenuation used to assess liver steatosis non-invasively. However, the standard method has some limitations. This study assessed the performance of a new CAP method by ex vivo and in vivo assessments. The major difference with the new method is that it uses ultrasound data continuously acquired during the imaging phase of the FibroScan examination. Seven reference tissue-mimicking phantoms were used to test the performance. In vivo performance was assessed in two cohorts (in total 195 patients) of patients using magnetic resonance imaging proton density fat fraction (MRI-PDFF) as a reference. The precision of CAP was improved by more than 50% on tissue-mimicking phantoms and 22%-41% in the in vivo cohort studies. The agreement between both methods was excellent, and the correlation between CAP and MRI-PDFF improved in both studies (0.71 to 0.74; 0.70 to 0.76). Using MRI-PDFF as a reference, the diagnostic performance of the new method was at least equal or superior (area under the receiver operating curve 0.889-0.900, 0.835-0.873). This study suggests that the new continuous CAP method can significantly improve the precision of CAP measurements ex vivo and in vivo.

Muscles adaptation to aging and training: architectural changes - a randomised trial.

BACKGROUND: To investigate how anatomical cross-sectional area and volume of quadriceps and triceps surae muscles were affected by ageing, and by resistance training in older and younger men, in vivo. METHODS: The old participants were randomly assigned to moderate (O55, n = 13) or high-load (O80, n = 14) resistance training intervention (12 weeks; 3 times/week) corresponding to 55% or 80% of one repetition maximum, respectively. Young men (Y55, n = 11) were assigned to the moderate-intensity strengthening exercise program. Each group received the exact same training volume on triceps surae and quadriceps group (Reps x Sets x Intensity). The fitting polynomial regression equations for each of anatomical cross-sectional area-muscle length curves were used to calculate muscle volume (contractile content) before and after 12 weeks using magnetic resonance imaging scans. RESULTS: Only Rectus femoris and medial gastrocnemius muscle showed a higher relative anatomical cross-sectional area in the young than the elderly on the proximal end. The old group displayed a higher absolute volume of non-contractile material than young men in triceps surae (+ 96%). After training, Y55, O55 and O80 showed an increase in total quadriceps (+ 4.3%; + 6.7%; 4.2% respectively) and triceps surae (+ 2.8%; + 7.5%; 4.3% respectively) volume. O55 demonstrated a greater increase on average gains compared to Y55, while no difference between O55 and O80 was observed. CONCLUSIONS: Muscle loss with aging is region-specific for some muscles and uniform for others. Equivalent strength training volume at moderate or high intensities increased muscle volume with no differences in muscle volume gains for old men. These data suggest that physical exercise at moderate intensity (55 to 60% of one repetition maximum) can reverse the aging related loss of muscle mass. TRIAL REGISTRATION: NCT03079180 in ClinicalTrials.gov . Registration date: March 14, 2017.

Viscoelastic shear properties of in vivo thigh muscles measured by MR elastography.

PURPOSE: To measure the viscoelastic properties of passive thigh muscles using multifrequency magnetic resonance elastography (MMRE) and rheological models. MATERIALS AND METHODS: Four muscles in five volunteers underwent MMRE tests set up inside a 1.5T magnetic resonance imaging (MRI) scanner. Compression excitation was generated with a driver attached around the thigh, and waves were generated at 70, 90, and 110 Hz. In vivo experimental viscoelastic parameters (G(ω) = G' + i G″) were extracted from the wavelength and attenuation measurements along a local profile in the direction of the wave's displacement. The data-processing method was validated on a phantom using MMRE and RheoSpectris tests. The complex modulus (G(ω)) related to elasticity (µ) and viscosity (η) was then determined using four rheological models. RESULTS: Zener was the best-fit model (χ ∼0.35 kPa) for the rheological parameters of all muscles. Similar behaviors for the elastic components for each muscle were found for the Zener and springpot models. The gracilis muscle showed higher elastic values (about 2 kPa) in both models compared to other muscles. The α-values for each muscle was equivalent to the ratio G″/G' at 90 Hz. CONCLUSION: MMRE tests associated with data processing demonstrated that the complex shear modulus G(ω) of passive muscles could be analyzed using two rheological models. The viscoelastic data can be used as a reference for future assessment of muscular dysfunction. J. Magn. Reson. Imaging 2015. J. Magn. Reson. Imaging 2016;43:1423-1433.

Quantifying the Elastic Property of Nine Thigh Muscles Using Magnetic Resonance Elastography.

BACKGROUND: Pathologies of the muscles can manifest different physiological and functional changes. To adapt treatment, it is necessary to characterize the elastic property (shear modulus) of single muscles. Previous studies have used magnetic resonance elastography (MRE), a technique based on MRI technology, to analyze the mechanical behavior of healthy and pathological muscles. The purpose of this study was to develop protocols using MRE to determine the shear modulus of nine thigh muscles at rest. METHODS: Twenty-nine healthy volunteers (mean age = 26 ± 3.41 years) with no muscle abnormalities underwent MRE tests (1.5 T MRI). Five MRE protocols were developed to quantify the shear moduli of the nine following thigh muscles at rest: rectus femoris (RF), vastus medialis (VM), vastus intermedius (VI), vastus lateralis (VL), sartorius (Sr), gracilis (Gr), semimembranosus (SM), semitendinosus (ST), and biceps (BC). In addition, the shear modulus of the subcutaneous adipose tissue was analyzed. RESULTS: The gracilis, sartorius, and semitendinosus muscles revealed a significantly higher shear modulus (µ_Gr = 6.15 ± 0.45 kPa, µ_ Sr = 5.15 ± 0.19 kPa, and µ_ ST = 5.32 ± 0.10 kPa, respectively) compared to other tissues (from µ_ RF = 3.91 ± 0.16 kPa to µ_VI = 4.23 ± 0.25 kPa). Subcutaneous adipose tissue had the lowest value (µ_adipose tissue = 3.04 ± 0.12 kPa) of all the tissues tested. CONCLUSION: The different elasticities measured between the tissues may be due to variations in the muscles' physiological and architectural compositions. Thus, the present protocol could be applied to injured muscles to identify their behavior of elastic property. Previous studies on muscle pathology found that quantification of the shear modulus could be used as a clinical protocol to identify pathological muscles and to follow-up effects of treatments and therapies. These data could also be used for modelling purposes.

Development of a phantom mimicking the functional and structural behaviors of the thigh muscles characterized with magnetic resonance elastography technique.

Magnetic Resonance Elastography (MRE) is a non invasive technique based on the propagation of shear waves in soft tissues providing the quantification of the mechanical properties [1]. MRE was successfully applied to healthy and pathological muscles. However, the MRE muscle methods must be further improved to characterize the deep muscles. A way will be to develop phantom mimicking the muscle behavior in order to set up new MRE protocol. Thus, the purpose of this study is to create a phantom composed of a similar skeletal muscle architecture (fiber, aponorosis) and equivalent elastic properties as a function of the muscle state (passive or active). Two homogeneous phantoms were manufactured with different concentrations of plastisol to simulate the elastic properties in relaxed (50% of plastisol) and contracted (70% of plastisol) muscle conditions. Moreover, teflon tubing pipes (D = 0.9 mm) were thread in the upper part of the phantom (50%) to represent the muscle fibers and a plastic sheet (8 × 15 cm) was also included in the middle of the phantom to mimic the aponeurosis structure. Subsequently, MRE tests were performed with two different pneumatic drivers, tube and round, (f = 90Hz) to analyze the effect of the type of driver on the wave propagation. Then, the wavelength was measured from the phase images to obtain the elastic properties (shear modulus). Both phantoms revealed elastic properties which were in the same range as in vivo muscle in passive (µ(50%) = 2.40 ± 0.18 kPa ) and active (6.24 ± 0.21 kPa) states. The impact of the type of driver showed higher values (about 1.2kPa) with the tube. The analysis of the wave behavior revealed a sliding along the plastic sheet as it was observed for in vivo muscle study. The wave was also sensitive to the presence of the fibers where gaps were identified. The present study demonstrates the ability of the phantom to mimic the structural and functional properties of the muscle.

Identification process based on shear wave propagation within a phantom using finite element modelling and magnetic resonance elastography.

Magnetic resonance elastography (MRE), based on shear wave propagation generated by a specific driver, is a non-invasive exam performed in clinical practice to improve the liver diagnosis. The purpose was to develop a finite element (FE) identification method for the mechanical characterisation of phantom mimicking soft tissues investigated with MRE technique. Thus, a 3D FE phantom model, composed of the realistic MRE liver boundary conditions, was developed to simulate the shear wave propagation with the software ABAQUS. The assumptions of homogeneity and elasticity were applied to the FE phantom model. Different ranges of mesh size, density and Poisson's ratio were tested in order to develop the most representative FE phantom model. The simulated wave displacement was visualised with a dynamic implicit analysis. Subsequently, an identification process was performed with a cost function and an optimisation loop provided the optimal elastic properties of the phantom. The present identification process was validated on a phantom model, and the perspective will be to apply this method on abdominal tissues for the set-up of new clinical MRE protocols that could be applied for the follow-up of the effects of treatments.

In vivo assessment of nervous fiber distribution in the intervertebral disc.

This present study aims to assess in vivo the nervous fibers distribution in the intervertebral disc using diffusion tensor imaging technique. Five healthy subjects participated into the data acquisition. Fiber extraction and tracking algorithms were used. The number of fibers in L4/5 disc ranges from 314 to 679 and the mean fiber length L4/5 in disc ranges from 8.22 ± 2.36 mm to 11.24 ± 5.17 mm. This study showed the feasibility of using diffusion tensor imaging technique to detect and assess the nervous fibers in the intervertebral discs. This could be of great clinical interest for the study of the correlations between these useful characteristics with pain levels on the low back pain patients.

Analysis of shear wave propagation derived from MR elastography in 3D thigh skeletal muscle using subject specific finite element model.

The purpose of this study was to develop a subject specific finite element model derived from MRI images to numerically analyze the MRE (magnetic resonance elastography) shear wave propagation within skeletal thigh muscles. A sagittal T2 CUBE MRI sequence was performed on the 20-cm thigh segment of a healthy male subject. Skin, adipose tissue, femoral bone and 11 muscles were manually segmented in order to have 3D smoothed solid and meshed models. These tissues were modeled with different constitutive laws. A transient modal dynamics analysis was applied to simulate the shear wave propagation within the thigh tissues. The effects of MRE experimental parameters (frequency, force) and the muscle material properties (shear modulus: C10) were analyzed through the simulated shear wave displacement within the vastus medialis muscle. The results showed a plausible range of frequencies (from 90Hz to 120 Hz), which could be used for MRE muscle protocol. The wave amplitude increased with the level of the force, revealing the importance of the boundary condition. Moreover, different shear displacement patterns were obtained as a function of the muscle mechanical properties. The present study is the first to analyze the shear wave propagation in skeletal muscles using a 3D subject specific finite element model. This study could be of great value to assist the experimenters in the set-up of MRE protocols.

A possible clinical tool to depict muscle elasticity mapping using magnetic resonance elastography.

INTRODUCTION: Characterization of muscle elasticity will improve the diagnosis and treatment of muscle disorders. The purpose is to compare the use of magnetic resonance elastography (MRE) and ultrasound elastography (USE) techniques to elucidate the MRE cartography of thigh muscles. METHODS: Both elastography techniques were performed on 5 children and 7 adults. Quantitative (MRE) and qualitative (USE) cartographies of muscle elasticity, as a function of muscle state and age, were obtained with shear waves and manual compression of the ultrasound probe, respectively. RESULTS: Similar cartographies of muscle elasticity were obtained with the 2 methods. The combination of both imaging techniques results in an improved depiction of the physiological changes associated with muscle state and age. CONCLUSIONS: This study demonstrates the feasibility of MRE for use as a clinical tool in the characterization of neuromuscular pathologies and for assessing the efficacy of specific treatments for muscle related diseases.

Analysis of liver viscosity behavior as a function of multifrequency magnetic resonance elastography (MMRE) postprocessing.

PURPOSE: To analyze the relevance of the viscosity measurement as a liver diagnostic marker. MATERIALS AND METHODS: To determine the level of fibrosis, a Fibroscan test was performed on 40 subjects (10 healthy volunteers and 30 patients). Subsequently, multifrequency magnetic resonance elastography (MMRE) tests were made with a pneumatic driver at 60, 70, and 80 Hz. Phase images were analyzed with two different postprocessing methods, without (Method 1) and with (Method 2) the inversion algorithm (IA), using rheological models (Voigt, springpot) in order to characterize the viscoelastic properties (viscosity: η and elasticity: µ). RESULTS: MRE cartography of the viscous tendency (G″MRE_M2 ) measured within the region of interest (ROI) of the liver increased as a function of the level of fibrosis. Similar results were also obtained for the viscosity (ηmodels_M1 ) calculated with a postprocessing without IA. However, the viscosity (ηmodels_M2 ) remained constant with the stage of fibrosis when the postprocessing was composed of an IA. The experimental (µMRE_M1 and G'MRE_M2 ) and rheological (µmodels_M2 and µmodels_M1 ) elasticities always increased with the level of fibrosis regardless of the postprocessing method. CONCLUSION: The variation of the liver viscosity parameter as a function of postprocessing revealed that this parameter should be further investigated to demonstrate its relevance in clinical practice.

Cutoff values for alcoholic liver fibrosis using magnetic resonance elastography technique.

BACKGROUND: Due to the lack of cutoff values validated for specific liver diseases, the purpose of this study was to set up specific magnetic resonance elastography (MRE) cutoff values for asymptomatic liver fibrosis in alcoholic patients. METHODS: Ninety patients underwent 3 clinical exams. The liver stiffness was measured locally with the Fibroscan, and globally through cartographies of shear modulus generated with MRE. The Fibroscan method was chosen as the gold standard to classify the fibrosis. The liver score was also obtained with the Fibrometer A, and the diagnostic performance of the methods was analyzed with receiver-operating characteristic (ROC) curves and cutoff values were calculated. RESULTS: Spearman correlation and area under the ROC curve revealed that MRE is a better diagnostic method than the Fibrometer A, to identify various levels of fibrosis. The results showed that the Fibrometer A was adapted for severe fibrosis. The MRE cutoff values are F1:2.20 kPa, F2:2.57 kPa, F3:3.31 kPa, and F4:4 kPa and were not influenced by the glutamic oxaloacetic transaminase level. By using the ultrasound cutoff values attributed for alcoholism, 66% of patients had a similar liver fibrosis diagnosis as the MRE cutoffs. However, both imaging techniques did not provide the same distribution for minor fibrosis. CONCLUSIONS: None of the imaging techniques (Fibroscan, MRE) could replace the gold standard of the biopsy. However, due to the risk and the unnecessary procedure for the present recruited alcoholic patients, the Fibroscan method was chosen as the reference. Since MRE is currently being used as a clinical exam, the present MRE cutoffs could aid clinicians with their diagnosis of liver fibrosis for alcoholism disease.

Characterization of a hyper-viscoelastic phantom mimicking biological soft tissue using an abdominal pneumatic driver with magnetic resonance elastography (MRE).

The purpose of this study was to create a polymer phantom mimicking the mechanical properties of soft tissues using experimental tests and rheological models. Multifrequency Magnetic Resonance Elastography (MMRE) tests were performed on the present phantom with a pneumatic driver to characterize the viscoelastic (µ, η) properties using Voigt, Maxwell, Zener and Springpot models. To optimize the MMRE protocol, the driver behavior was analyzed with a vibrometer. Moreover, the hyperelastic properties of the phantom were determined using compressive tests and Mooney-Rivlin model. The range of frequency to be used with the round driver was found between 60 Hz and 100 Hz as it exhibits one type of vibration mode for the membrane. MRE analysis revealed an increase in the shear modulus with frequency reflecting the viscoelastic properties of the phantom showing similar characteristic of soft tissues. Rheological results demonstrated that Springpot model better revealed the viscoelastic properties (µ=3.45 kPa, η=6.17 Pas) of the phantom and the Mooney-Rivlin coefficients were C(10)=1.09.10(-2) MPa and C(01)=-8.96.10(-3) MPa corresponding to µ=3.95 kPa. These studies suggest that the phantom, mimicking soft tissue, could be used for preliminary MRE tests to identify the optimal parameters necessary for in vivo investigations. Further developments of the phantom may allow clinicians to more accurately mimic healthy and pathological soft tissues using MRE.

Stiffness imaging of the kidney and adjacent abdominal tissues measured simultaneously using magnetic resonance elastography.

To date, non-invasive methods to detect kidney malignancies and mild tumors remain a challenge. The purpose of this study was to establish the proper imaging protocol to determine kidney stiffness and its spatial distribution within the various kidney compartments such as the renal sinus, medulla, and cortex. Here, we have used magnetic resonance elastography (MRE) along with coronal oblique acquisition to simultaneously measure kidney stiffness in comparison with other tissues including the liver, spleen, and psoas.

Analysis of thigh muscle stiffness from childhood to adulthood using magnetic resonance elastography (MRE) technique.

BACKGROUND: Magnetic resonance elastography has been performed in healthy and pathological muscles in order to provide clinicians with quantitative muscle stiffness data. However, there is a lack of data on pediatric muscle. Therefore, the present work studies age-related changes of the mechanical properties. METHODS: 26 healthy subjects composed of 7 children (8-12 years), 9 young adults (24-29 years) and 10 middle-aged adults (53-58 years) underwent a magnetic resonance elastography test. Shear modulus (µ) and its spatial distribution, as well as the attenuation coefficient (α) were measured on the vastus medialis muscle at rest and at contracted conditions (10% and 20% of the maximum voluntary contraction) for each group. FINDINGS: The shear modulus linearly increases with the degree of contraction for young adults while it is maximum at 10% of the maximum voluntary contraction for children (µ_(children_10%)=14.9kPa (SD 2.18)) and middle-aged adults (µ_(middle-aged_10%)=10.42kPa (SD 1.38)). Mapping of shear modulus revealed a diffuse distribution of colors reflecting differences in muscle physiological activity as a function of age. The attenuation coefficient showed a similar behavior for all groups, i.e. a decrease from the relaxed to the contracted states. INTERPRETATION: This study demonstrates that the magnetic resonance elastography technique is sensitive enough to detect changes in muscle mechanical properties for children, middle-aged and young adults and could provide clinicians with a muscle reference data base as a function of age, improving the diagnosis of muscular dystrophy.

Characterization of muscle architecture in children and adults using magnetic resonance elastography and ultrasound techniques.

The purpose of this study is to characterize the muscle architecture of children and adults using magnetic resonance elastography and ultrasound techniques. Five children (8-12 yr) and seven adults (24-58 yr) underwent both tests on the vastus medialis muscle at relaxed and contracted (10% and 20% of MVC) states. Longitudinal ultrasonic images were performed in the same area as the phase image showing the shear wave's propagation. Two geometrical parameters were defined: the wave angle (α(_MRE)) corresponding to the shear wave propagation and the fascicule angle (α(_US)) tracking the path of fascicles. Moreover, shear modulus was measured at different localizations within the muscle and in the subcutaneous adipose tissue. The association of both techniques demonstrates that the shear wave propagation follows the muscle fascicles path, reflecting the internal muscle architecture. At rest, ultrasound images revealed waves propagating parallel to the children fascicle while adults showed oblique waves corresponding to already oriented (α(_US)=15.4±2.54°) muscle fascicles. In contraction, the waves' propagation were in an oblique direction for children (α(_US_10%MVC)=10.6±2.27°, α(_US_20%MVC)=10.2±2.29°) as well as adults (α(_US_10%MVC)=15.4±2.54°, α(_US_20%MVC)=17.2±2.44°). A stiffness variation (1 kPa) was found between the upper and lower parts of the adult VM muscle and a lower stiffness (1.85±0.17 kPa) was measured in the subcutaneous adipose tissue. This study demonstrates the feasibility of the MRE technique to provide geometrical insights from the children and adults muscles and to characterize different physiological media.

Measurement of liver stiffness with two imaging techniques: magnetic resonance elastography and ultrasound elastometry.

PURPOSE: To cross-validate the magnetic resonance elastography (MRE) technique with a clinical device, based on an ultrasound elastometry system called Fibroscan. MATERIALS AND METHODS: Ten healthy subjects underwent an MRE and a Fibroscan test. The MRE technique used a round pneumatic driver at 60 Hz to generate shear waves inside the liver. An elastogram representing a map of the liver stiffness was generated allowing for the measurement of the average liver stiffness inside a region of interest. The Fibroscan technique used an ultrasound probe (3.5 MHz) composed of a vibrator that sent low-frequency (50 Hz) shear waves inside the right liver lobe. The probe acts as an emitter-receptor that measures the velocity of the waves propagated inside the liver tissue. RESULTS: The mean shear stiffness measured with the MRE and Fibroscan techniques were 1.95+/-0.06 kPa and 1.79+/-0.30 kPa, respectively. A higher standard deviation was found for the same subject with Fibroscan. CONCLUSION: This study shows why MRE should be investigated beyond the Fibroscan. The MRE technique provided elasticity of the entire liver, meanwhile the Fibroscan provided values of elasticity locally.