Ultrasound shear wave velocity in skeletal muscle: A reproducibility study

Estimating the viscoelastic anisotropy of human skin through high-frequency ultrasound elastography

BACKGROUND

The skin is the largest organ of the human body and serves distinct functions in protecting the body. The viscoelastic properties of the skin play a key role in supporting the skin-healing process, also it may be changed due to some skin diseases.

PROPOSE

In this study, high-frequency ultrasound (HFUS) elastography based on a Lamb wave model was used to noninvasively assess the viscoelastic anisotropy of human skin.

METHOD

Elastic waves were generated through an external vibrator, and the wave propagation velocity was measured through 40 MHz ultrafast HFUS imaging. Through the use of a thin-layer gelatin phantom, HFUS elastography was verified to produce highly accurate estimates of elasticity and viscosity. In a human study involving five volunteers, viscoelastic anisotropy was assessed by rotating an ultrasound transducer 360°.

RESULTS

An oval-shaped pattern in the elasticity of human forearm skin was identified, indicating the high elastic anisotropy of skin; the average elastic moduli were 24.90 ± 6.63 and 13.64 ± 2.67 kPa along and across the collagen fiber orientation, respectively. The average viscosity of all the recruited volunteers was 3.23 ± 0.93 Pa·s.

CONCLUSIONS

Although the examined skin exhibited elastic anisotropy, no evident viscosity anisotropy was observed.

Quantitative diagnosis of early acute compartment syndrome using two-dimensional shear wave elastography in a rabbit model

PURPOSE

This study explored the association of the elasticity modulus and shear wave velocity (SWV) of the tibialis anterior muscle, as measured by two-dimensional shear wave elastography (2D-SWE), with the intracompartmental pressure (ICP) determined using the Whitesides method in a New Zealand rabbit model of acute compartment syndrome (ACS). Additionally, it evaluated the viability of 2D-SWE as a noninvasive, quantitative tool for the early detection of ACS.

METHODS

An ACS model was established through direct external compression by applying pressure bandaging to the lower legs of 15 New Zealand rabbits using neonatal blood pressure cuffs. Another five animals represented a non-modeled control group. To measure the elasticity modulus and SWV of the tibialis anterior muscles, 2D-SWE was employed. Blood oxygen saturation, serum creatine kinase (CK), and myoglobin levels were monitored. Subsequently, the anterior tibial compartment was dissected, and the tibialis anterior was removed for hematoxylin and eosin staining to assess muscle injury.

RESULTS

The elasticity modulus and SWV of the tibialis anterior muscle increased with compression duration, as did serum CK and myoglobin levels. ICP was strongly positively correlated with these parameters, particularly mean velocity (r=0.942, P<0.001) and CK (r=0.942, P<0.001). Blood oxygen saturation was negatively correlated with ICP (r=-0.887, P<0.001). Histological analysis indicated progressive muscle cell swelling over time, with damage transitioning from reversible to irreversible and culminating in necrosis.

CONCLUSION

In a rabbit ACS model, ICP was strongly positively correlated with muscle elasticity modulus/SWV. Consequently, 2D-SWE may represent a novel tool for assessing early-phase ACS.

Establishment and Validation of a Predictive Model for Sarcopenia Based on 2-D Ultrasound and Shear Wave Elastography in the Medial Gastrocnemius Muscle

OBJECTIVE

To develop and validate a predictive model for sarcopenia.

METHODS

A total of 240 subjects who visited our hospital between August 2021 and May 2023 were randomly divided by time of entry into a training set containing 2/3 of patients and a validation set containing 1/3 of patients. The muscle thickness (MT), echo intensity (EI), and shear wave velocity (SWV) of the medial gastrocnemius muscle were measured. Indicators that were meaningful in the univariate analysis in the training set were included in a binary logistic regression to derive a regression model, and the model was evaluated using a consistency index, calibration plot, and clinical validity curve. Diagnostic efficacy and clinical applicability were compared between the model and unifactorial indicators.

RESULTS

Four meaningful variables, age, body mass index (BMI), MT, and SWV, were screened into the predictive model. The model was Logit Y = 21.292 + 0.065 × Age - 0.411 × BMI - 0.524 × MT - 3.072 × SWV. The model was well differentiated with an internally validated C-index of 0.924 and an external validation C-index of 0.914. The calibration plot predicted probabilities against actual probabilities showed excellent agreement. The specificity, sensitivity, and Youden's index of the model were 73.80%, 97.40%, and 71.20%, respectively, when using the diagnostic cut-off value of >0.279 for sarcopenia. The logistic model had higher diagnostic efficacy (p < 0.001) and higher net clinical benefit (p < 0.001) over the same threshold range compared to indicators.

CONCLUSION

The logistic model of sarcopenia has been justified to have good discriminatory, calibrated, and clinical validity, and has higher diagnostic value than indicators.

Quantifying lower limb muscle stiffness in typically developing children and adolescents using acoustic radiation force impulse shear wave elastography (ARFI/SWE)-a pilot study

OBJECTIVE

To investigate and quantify age-related changes in lower limb muscle stiffness in typically developing children and adolescents using acoustic radiation force impulse shear wave elastography.

MATERIALS AND METHODS

Shear wave velocities of bilateral rectus femoris, tibialis anterior, and medial gastrocnemius muscles at rest were obtained in typically developing children and adolescents aged 3 to 18 years. The participants were classified into three age groups: Group 1 (children), 3 to 7 years old; Group 2, 8 to 12 (pre-adolescent); and Group 3 (adolescent), 13 to 18. The shear wave velocities of muscle were compared across the three age groups, as well as compared between right- and left-side limbs. The correlation between shear wave velocities and body weight or body mass index was assessed.

RESULTS

Of the 47 participants, 21 were in Group 1, 17 in Group 2, and 9 in Group 3. There were no significant differences among the three age groups' shear wave velocities of bilateral lower limb muscles, and no significant differences between right and left sides. There was no correlation between muscle stiffness and body weight or body mass index.

CONCLUSION

The present pilot study applied acoustic radiation force impulse shear wave elastography to quantify lower limb muscle stiffness in typically developing children and adolescents aged 3 to 18 years, suggesting no marked change in muscle stiffness occurs as they develop.

The use of shear-wave elastography for the assessment of muscle spasticity in patients with cerebral palsy, a systematic review

We explore the use of shear wave elastography (SWE) for assessing muscle stiffness and treatment response in cerebral palsy (CP) children by way of a systematic review. SWE offers real-time muscle stiffness measurements, showing significant differences between CP patients and controls. Studies suggest that SWE can be used to follow muscle stiffness post-botulinum toxin treatment, correlating with clinical improvement. However, methodological variations and small sample sizes prevent comparison between different studies. Standardized protocols could enhance SWE's clinical utility. In conclusion, SWE holds promise for CP management, though standardized methodologies and larger studies are needed to validate its efficacy and integration into clinical practice.

Explorative study using ultrasound time-harmonic elastography for stiffness-based quantification of skeletal muscle function

Time-harmonic elastography (THE) is an emerging ultrasound imaging technique that allows full-field mapping of the stiffness of deep biological tissues. THE's unique ability to rapidly capture stiffness in multiple tissues has never been applied for imaging skeletal muscle. Therefore, we addressed the lack of data on temporal changes in skeletal muscle stiffness while simultaneously covering stiffness of different muscles. Acquiring repeated THE scans every five seconds we quantified shear-wave speed (SWS) as a marker of stiffness of the long head (LHB) and short head (SHB) of biceps brachii and of the brachialis muscle (B) in ten healthy volunteers. SWS was continuously acquired during a 3-min isometric preloading phase, a 3-min loading phase with different weights (4, 8, and 12 kg), and a 9-min postloading phase. In addition, we analyzed temporal SWS standard deviation (SD) as a marker of muscle contraction regulation. Our results (median [min, max]) showed both SWS at preloading (LHB: 1.04 [0.94, 1.12] m/s, SHB: 0.86 [0.78, 0.94] m/s, B: 0.96 [0.87, 1.09] m/s, p < 0.001) and the increase in SWS with loading weight to be muscle-specific (LHB: 0.010 [0.002, 0.019] m/s/kg, SHB: 0.022 [0.017, 0.042] m/s/kg, B: 0.039 [0.019, 0.062] m/s/kg, p < 0.001). Additionally, SWS during loading increased continuously over time by 0.022 [0.004, 0.051] m/s/min (p < 0.01). Using an exponential decay model, we found an average relaxation time of 27 seconds during postloading. Analogously, SWS SD at preloading was also muscle-specific (LHB: 0.018 [0.011, 0.029] m/s, SHB: 0.021 [0.015, 0.027] m/s, B: 0.024 [0.018, 0.037] m/s, p < 0.05) and increased by 0.005 [0.003, 0.008] m/s/kg (p < 0.01) with loading. SWS SD did not change over loading time and decreased immediately in the postloading phase. Taken together, THE of skeletal muscle is a promising imaging technique for in vivo quantification of stiffness and stiffness changes in multiple muscle groups within seconds. Both the magnitude of stiffness changes and their temporal variation during isometric exercise may reflect the functional status of skeletal muscle and provide additional information to the morphological measures obtained by conventional imaging modalities.

2D shear wave elastography for the assessment of quadriceps entheses-a methodological study

OBJECTIVE

To establish the scanning protocol for 2-dimensional shear wave elastography (SWE) on normal entheses by investigating the possible confounding factors that may increase the variability of measured elasticity.

MATERIAL AND METHODS

30 normal quadriceps entheses were scanned using SWE to compare the stiffness and coefficient variation by changing the ultrasonic coupling gel thickness, knee position, region of interest size, and scanning plane.

RESULTS

No significant difference in median shear wave velocity (SWV) was observed in different coupling gel thicknesses. The median SWV was higher in the knee flexion position than in the extended position (p < 0.001). Increased knee flexion led to stiffer quadriceps enthesis and higher SWV (ρ = 0.8, p < 0.001). The median SWV was higher when the diameter region of interest was 4.0 mm than 2.0 mm (p = 0.001). The median SWV was higher in the transverse plane than in the longitudinal plane (p < 0.001). Strong correlation was found between SWV and the degree of the shear wave to muscle fiber direction (ρ = 0.8, p < 0.001). The coefficient variation was lower in a gel thickness of 2.5 cm, with an extended knee, a region of interest of 2.0 mm, and a longitudinal plane (p > 0.05). For interobserver reliability for the proposed protocol, the intraclass correlation coefficients was 0.763.

CONCLUSION

In this study, we determined supine position with the knee extended; using 2.0 mm diameter region of interest and image acquisition at the longitudinal plane with thicker layer coupling gel seems most appropriate to reliably image healthy quadriceps entheses with SWE.

Achilles tendon and triceps surae muscle properties in athletes

PURPOSE

The aim of this study was to investigate internal Achilles tendon (AT) displacement, AT shear wave velocity (SWV), and triceps surae (TS) muscle shear modulus in athletes.

METHODS

Internal AT displacement was assessed using ultrasound during isometric contraction. Shear wave elastography was used to assess AT SWV (m × s-1) at rest and TS muscle shear modulus (kPa) during passive ankle dorsiflexion.

RESULTS

A total of 131 athletes participated in this study. Athletes who had not exercised within two days had greater AT non-uniformity and mean anterior tendon displacement, and lower SWV at the proximal AT measurement site (mean difference [95% CI]: 1.8 mm [0.6-2.9], p = 0.003; 1.6 mm [0.2-2.9], p = 0.021; - 0.9 m × s-1 [- 1.6 to - 0.2], p = 0.014, respectively). Male basketball players had a lower mean AT displacement compared to gymnasts (- 3.7 mm [- 6.9 to - 0.5], p = 0.042), with the difference localised in the anterior half of the tendon (- 5.1 mm [- 9.0 to - 1.1], p = 0.022). Male gymnasts had a smaller absolute difference in medial gastrocnemius-minus-soleus shear modulus than basketball players (59.6 kPa [29.0-90.2], p < 0.001) and track and field athletes (52.7 kPa [19.2-86.3], p = 0.004). Intraclass correlation coefficients of measurements ranged from 0.720 to 0.937 for internal AT displacement, from 0.696 to 0.936 for AT SWE, and from 0.570 to 0.890 for TS muscles.

CONCLUSION

This study provides a reliability assessment of muscle and tendon SWV. The relative differences in passive TS muscle shear modulus suggest sport-specific adaptation. Importantly, in healthy individuals, lower AT displacement after exercise may reflect the time required for tendon recovery.

Rotational 3D shear wave elasticity imaging: Effect of knee flexion on 3D shear wave propagation in in vivo vastus lateralis

Skeletal muscle is a complex tissue, exhibiting not only direction-dependent material properties (commonly modeled as a transversely isotropic material), but also changes in observed material properties due to factors such as contraction and passive stretch. In this work, we evaluated the effect of muscle passive stretch on shear wave propagation along and across the muscle fibers using a rotational 3D shear wave elasticity imaging system and automatic analysis methods. We imaged the vastus lateralis of 10 healthy volunteers, modulating passive stretch by imaging at 8 different knee flexion angles (controlled by a BioDex system). In addition to demonstrating the ability of this acquisition and automatic processing system to estimate muscle shear moduli over a range of values, we evaluated potential higher order biomarkers for muscle health that capture the change in muscle stiffness along and across the fibers with changing knee flexion. The median within-subject variability of these biomarkers is found to be <16%, suggesting promise as a repeatable clinical metric. Additionally, we report an unexpected observation: that shear wave signal amplitude along the fibers increases with increasing flexion and muscle stiffness, which is not predicted by transversely isotropic (TI) material simulations. This observation may point to an additional potential biomarker for muscle health or inform other material modeling choices for muscle.

Chinese Ultrasound Doctors Association Guideline on Operational Standards for 2-D Shear Wave Elastography Examination of Musculoskeletal Tissues

The Ultrasound Physician Branch of the Chinese Medical Doctor Association sought to develop evidence-based recommendations on the operational standards for 2-D shear wave elastography examination of musculoskeletal tissues. A consensus panel of 22 Chinese musculoskeletal ultrasound experts reviewed current scientific evidence and proposed a set of 12 recommendations for 13 key issues, including instruments, operating methods, influencing factors and image interpretation. A final consensus was reached through discussion and voting. On the basis of research evidence and expert opinions, the strength of recommendation for each proposition was assessed using a visual analog scale, while further emphasizing the best available evidence during the question-and-answer session. These expert consensus guidelines encourage facilitation of the standardization of clinical practices for collecting and reporting shear wave elastography data.

Acute Effects of Stretching Exercises on Posterior Chain: Analysis of Shear Modulus by Elastography SSI

The posterior chain muscles of the lower limb include the hamstrings and triceps surae, along with the Achilles tendon. This study aimed to investigate the acute effects of static stretching exercises commonly used in clinical and training settings on the shear modulus (µ) of these muscles and tendon using Supersonic Shear-Wave Imaging (SSI) elastography. Fifteen healthy adults participated in the study, performing stretching exercises for hamstrings and triceps surae. Shear modulus and joint range of motion (ROM) were measured before and after the stretching protocols. The hip and ankle mean ROM significantly increased by 19.27% and 24.10%, respectively. However, the stretching protocol did not significantly alter in µ of the hamstrings, the gastrocnemius muscles, and the Achilles tendon. K-means clustering analysis identified a group where the subjects with lower initial ROM showed higher amplitude gains and a significant decrease in the semimembranosus stiffness after stretching. These findings suggest that the stretching protocol was effective in improving joint mobility but not sufficient to elicit immediate mechanical changes in muscle and tendon stiffness. Neural adaptations and nonmuscular structures might contribute to increased ROM. The study highlights the importance of considering individual initial ROM and subsequent responses when evaluating the effects of stretching exercises on muscle and tendon properties.

Changes in Lower Extremity Muscle Quantity and Quality in Patients with Subacute Stroke

OBJECTIVE

To analyze the changes in muscle mass and quality with time on the paretic and non-paretic sides in subacute stroke patients and identify correlations between the variation of muscle mass and quality and lower limb functions.

METHODS

Thirty hemiplegia patients diagnosed with stroke participated in this study. To evaluate poststroke muscle changes, longitudinal measurement of muscle mass and quality was conducted with bilateral lower limbs. The elastic shear modulus was measured using shear wave elastography and muscle thickness (MT) of rectus femoris, vastus intermedius, vastus lateralis (VL), vastus medialis, tibialis anterior, and gastrocnemius (GCM) muscles. Functional evaluation was performed using Berg Balance Scale (BBS), Five Times Sit to Stand Test (FTSST). Follow-up was performed at discharge. The muscle mass and quality were compared according to time. We analyzed whether muscle quantity and quality were related to function.

RESULTS

MT demonstrated no significant change with time. The elastic shear modulus increased significantly in the paretic VL and GCM muscles and did not change significantly in the muscles on the non-paretic side. Correlation analysis detected that elastic shear modulus in the VL has a cross-sectional negative relationship between BBS and positive relationship between FTSST. There were significant correlation between variation of FTSST and the variation of the elastic shear modulus in VL.

CONCLUSION

Only paretic VL and GCM muscle quality changed in subacute stroke patients and muscle's property related to lower limb functions. Therefore, the lower extremity requires an approach to muscle quality rather than quantity for subacute stroke patients.

Visualization of Human Hand Tendon Mechanical Anisotropy in 3-D Using High- Frequency Dual-Direction Shear Wave Imaging

High-resolution ultrasound shear wave elastography has been used to determine the mechanical properties of hand tendons. However, because of fiber orientation, tendons have anisotropic properties; this results in differences in shear wave velocity (SWV) between ultrasound scanning cross sections. Rotating transducers can be used to achieve full-angle scanning. However, this technique is inconvenient to implement in clinical settings. Therefore, in this study, high-frequency ultrasound (HFUS) dual-direction shear wave imaging (DDSWI) based on two external vibrators was used to create both transverse and longitudinal shear waves in the human flexor carpi radialis tendon. SWV maps from two directions were obtained using 40-MHz ultrafast imaging at the same scanning cross section. The anisotropic map was calculated pixel by pixel, and 3-D information was obtained using mechanical scanning. A standard phantom experiment was then conducted to verify the performance of the proposed HFUS DDSWI technique. Human studies were also conducted where volunteers assumed three hand postures: relaxed (Rel), full fist (FF), and tabletop (TT). The experimental results indicated that both the transverse and longitudinal SWVs increased due to tendon flexion. The transverse SWV surpassed the longitudinal SWV in all cases. The average anisotropic ratios for the Rel, FF, and TT hand postures were 1.78, 2.01, and 2.21, respectively. Both the transverse and the longitudinal SWVs were higher at the central region of the tendon than at the surrounding region. In conclusion, the proposed HFUS DDSWI technique is a high-resolution imaging technique capable of characterizing the anisotropic properties of tendons in clinical applications.

The effects of hip- vs. knee-dominant hamstring exercise on biceps femoris morphology, strength, and sprint performance: a randomized intervention trial protocol

BACKGROUND

The hamstrings are an important muscle group that contribute to horizontal force during sprint acceleration and are also the most injured muscle group in running-based sports. Given the significant time loss associated with hamstrings injury and impaired sprinting performance following return to sport, identifying exercises that drive adaptations that are both protective of strain injury and beneficial to sprint performance is important for the strength and conditioning professional. This paper describes the study protocol investigating the effects of a 6-week training program using either the hip-dominant Romanian deadlift (RDL) or the knee-dominant Nordic hamstring exercise (NHE) on hamstring strain injury risk factors and sprint performance.

METHODS

A permuted block randomized (1:1 allocation) intervention trial will be conducted involving young, physically-active men and women. A target sample size of 32 will be recruited and enrolled participants will undergo baseline testing involving extended-field-of-view ultrasound imaging and shear wave elastography of the biceps femoris long head muscle, maximal hamstrings strength testing in both the RDL and NHE, and on-field sprint performance and biomechanics. Participants will complete the 6-week training intervention using either the RDL or NHE, according to group allocation. Baseline testing will be repeated at the end of the 6-week intervention followed by 2 weeks of detraining and a final testing session. The primary outcome will be regional changes in fascicle length with secondary outcomes including pennation angle, muscle cross sectional area, hamstring strength, and maximal sprint performance and biomechanics. An exploratory aim will determine changes in shear wave velocity.

DISCUSSION

Despite extensive research showing the benefits of the NHE on reducing hamstring strain injury risk, alternative exercises, such as the RDL, may offer similar or potentially even greater benefits. The findings of this study will aim to inform future researchers and practitioners investigating alternatives to the NHE, such as the RDL, in terms of their effectiveness in reducing rates of hamstring strain injury in larger scale prospective intervention studies.

TRIAL REGISTRATION

The trial is prospectively registered on ClinicalTrials.gov (NCT05455346; July 15, 2022).

Measuring Shear Wave Velocity in Adult Skeletal Muscle with Ultrasound 2-D Shear Wave Elastography: A Scoping Review

Ultrasound 2-D shear wave elastography (US 2D-SWE) is a non-invasive, cost-effective tool for quantifying tissue stiffness. Amidst growing interest in US 2D-SWE for musculoskeletal research, it has been recommended that shear wave velocity (SWV) should be reported instead of elastic moduli to avoid introducing unwanted error into the data. This scoping review examined the evolving use of US 2D-SWE to measure SWV in skeletal muscle and identified strengths and weaknesses to guide future research. We searched electronic databases and key review reference lists to identify articles published between January 2000 and May 2021. Two reviewers assessed the eligibility of records during title/abstract and full-text screening, and one reviewer extracted and coded the data. Sixty-six studies met the eligibility criteria, of which 58 were published in 2017 or later. We found a striking lack of consensus regarding the effects of age and sex on skeletal muscle SWV, and widely variable reliability values. Substantial differences in methodology between studies suggest a pressing need for developing standardized, validated scanning protocols. This scoping review illustrates the breadth of application for US 2D-SWE in musculoskeletal research, and the data synthesis exposed several notable inconsistencies and gaps in current literature that warrant consideration in future studies.

Shear Wave Elastography for Detecting Calf Muscle Stiffness: An Effective Tool for Assessing Sarcopenia

OBJECTIVES

To explore the feasibility of shear wave elastography for evaluating sarcopenia.

METHODS

The shear wave velocities (SWV) of the tibialis anterior, medial gastrocnemius, and soleus were measured in 130 subjects in the Second Affiliated Hospital of Fujian Medical University from January 2021 to June 2022. Consistency was evaluated in 20 cases using the intraclass correlation coefficient. According to the 2019 Asian Working Group for Sarcopenia（AWGS） diagnostic criteria, the patients were divided into a healthy and a sarcopenia group. The differences in SWV between the two groups were compared, and their correlation between calf muscles and muscle mass, grip strength, and pace were analyzed. The diagnostic cutoff value of calf muscle SWV for sarcopenia was obtained using receiver operating characteristic (ROC) curves, and the diagnostic efficacy of different ROC curves was compared.

RESULTS

The SWV inter-group and intra-group correlation coefficients of the three lower limbs muscles were all greater than 0.85. Moreover, the corresponding SWV in the sarcopenia group were significantly smaller than those in the healthy control group (P < .05). Further, SWV were positively correlated with the appendicular skeletal muscle mass index (ASMI), grip strength, and gait speed. Finally, the SWV of the anterior tibialis and medial gastrocnemius muscles were 3.02 and 2.26 m/s, respectively, and their diagnostic efficacy for sarcopenia did not differ significantly (Z = 0.190, P = .8497).

CONCLUSION

SWE can be used to detect the hardness of the anterior tibialis and medial gastrocnemius, calculate their muscle mass as an effective tool to evaluate sarcopenia.

Nondestructive ultrasound evaluation of microstructure-related material parameters of skeletal muscle: An in silico and in vitro study

Direct and nondestructive assessment of material properties of skeletal muscle in vivo shall advance our understanding of intact muscle mechanics and facilitate personalized interventions. However, this is challenged by intricate hierarchical microstructure of the skeletal muscle. We have previously regarded the skeletal muscle as a composite of myofibers and extracellular matrix (ECM), formulated shear wave propagation in the undeformed muscle using the acoustoelastic theory, and preliminarily demonstrated that ultrasound-based shear wave elastography (SWE) could estimate microstructure-related material parameters (MRMPs): myofiber stiffness μ_f, ECM stiffness μ_m, and myofiber volume ratio V_f. The proposed method warrants further validation but is hampered by the lack of ground truth values of MRMPs. In this study, we presented analytical and experimental validations of the proposed method using finite-element (FE) simulations and 3D-printed hydrogel phantoms, respectively. Three combinations of different physiologically relevant MRMPs were used in the FE simulations where shear wave propagations in the corresponding composite media were simulated. Two 3D-printed hydrogel phantoms with the MRMPs close to those of a real skeletal muscle (i.e., μ_f=2.02kPa, μ_m=52.42kPa, and V_f=0.675,0.832) for ultrasound imaging were fabricated by an alginate-based hydrogel printing protocol that we modified and optimized from the freeform reversible embedding of suspended hydrogels (FRESH) method in literature. Average percent errors of (μ_f,μ_m,V_f) estimates were found to be (2.7%,7.3%,2.4%)in silico and (3.0%,8.0%,9.9%)in vitro. This quantitative study corroborated the potential of our proposed theoretical model along with ultrasound SWE for uncovering microstructural characteristics of the skeletal muscle in an entirely nondestructive way.

Repeatability of Rotational 3-D Shear Wave Elasticity Imaging Measurements in Skeletal Muscle

Shear wave elasticity imaging (SWEI) usually assumes an isotropic material; however, skeletal muscle is typically modeled as a transversely isotropic material with independent shear wave speeds in the directions along and across the muscle fibers. To capture these direction-dependent properties, we implemented a rotational 3-D SWEI system that measures the shear wave speed both along and across the fibers in a single 3-D acquisition, with automatic detection of the muscle fiber orientation. We tested and examined the repeatability of this system's measurements in the vastus lateralis of 10 healthy volunteers. The average coefficient of variation of the measurements from this 3-D SWEI system was 5.3% along the fibers and 8.1% across the fibers. When compared with estimated respective 2-D SWEI values of 16.0% and 83.4%, these results suggest using 3-D SWEI has the potential to improve the precision of SWEI measurements in muscle. Additionally, we observed no significant difference in shear wave speed between the dominant and non-dominant legs along (p = 0.26) or across (p = 0.65) the muscle fibers.

Assessment of ultrasound shear wave elastography: An animal ex-vivo study

OBJECTIVES

To explore the influence of the surrounding environment of the target tissue, lesion size, and rectangular sampling box size on shear wave speed (SWS).

METHODS

The tendon SWS was acquired ex-vivo. Then the tendons were dissected and buried in the couplant (gel) and evaluated by two-dimensional shear wave elastography (2D-SWE). Finally, the tendons were placed in the isolated muscles to simulate the intramuscular lesions, and their elasticity was tested under two rectangular sampling box conditions. The isolated complete liver SWS was acquired. Similarly, the large and small pieces of livers were cut out, placed in the muscles, and assessed by SWE under two rectangular sampling box conditions. The SWS acquired under different conditions was compared. Variability was evaluated using the coefficient of variation (CV). The intraclass correlation coefficient (ICC) was used to evaluate repeatability.

RESULTS

The SWS of the tendons ex-vivo, buried in the couplant and placed in the isolated muscles showed significant differences (p < 0.001). The ex-vivo condition produced the highest SWS and CV values. There were significant differences in SWS of livers with different sizes placed in muscles (p < 0.001). The highest SWS value was associated with small pieces of livers. No significant difference was found in SWS acquired under different rectangular box sizes (p > 0.05).

CONCLUSIONS

Under the present study conditions, the surrounding environment of the target tissue makes a big difference to lesion SWS values. The lesion size will affect the assessment of its inherent elasticity. The size of the sampling frame has no significant effect on the tissue SWS.

Regional shear wave elastography of Achilles tendinopathy in symptomatic versus contralateral Achilles tendons

OBJECTIVES

Ultrasound often corroborates clinical diagnosis of Achilles tendinopathy (AT). Traditional measures assess macromorphological features or use qualitative grading scales, primarily focused within the free tendon. Shear wave imaging can non-invasively quantify tendon elasticity, yet it is unknown if proximal structures are affected by tendon pathology. The purpose of the study was to determine the characteristics of both traditional sonographic measures and regional shear wave speed (SWS) between limbs in patients with AT.

METHODS

Twenty patients with chronic AT were recruited. Traditional sonographic measures of tendon structure were measured. Regional SWS was collected in a resting ankle position along the entire length of the tendon bilaterally. SWS measures were extracted and interpolated across evenly distributed points corresponding to the free tendon (FT), soleus aponeurosis (SA), and gastrocnemius aponeurosis (GA). Comparisons were made between limbs in both traditional sonographic measures and regional SWS.

RESULTS

Symptomatic tendons were thicker (10.2 (1.9) vs. 6.8 (1.8) mm; p < 0.001) and had more hyperemia (p = 0.001) and hypoechogenicity (p = 0.002) than the contralateral tendon. Regional SWS in the FT was lower in the symptomatic limb compared to the contralateral limb (11.53 [10.99, 12.07] vs. 10.97 [10.43, 11.51]; p = 0.03). No differences between limbs were found for the SA (p = 0.13) or GA (p = 0.99).

CONCLUSIONS

Lower SWS was only observed in the FT in AT patients, indicating that alterations in tendon elasticity associated with AT were localized to the FT and did not involve the proximal passive tendon structures.

KEY POINTS

• Baseline characteristics of a pilot sample of 20 subjects suffering from chronic Achilles tendinopathy showed differences in conventional sonographic measures of tendon thickness, qualitatively assessed hypoechogenicity, hyperemia, and quantitative measures of shear wave speed. • Regional shear wave speeds were lower in the free tendon but not in the proximal regions of the soleus or gastrocnemius aponeuroses in Achilles tendinopathy patients. • Using shear wave imaging to estimate tendon stiffness may prove beneficial for clinical validation studies to address important topics such as return to activity and the effectiveness of rehabilitation protocols.

Variability of Biceps Muscle Stiffness Measured Using Shear Wave Elastography at Different Anatomical Locations With Different Ultrasound Machines

Shear wave elastography is an emerging diagnostic tool used to assess for changes in the stiffness of muscle. Each region of the muscle may have a different stiffness; therefore, the anatomical region should be carefully selected. Machine vendors each have unique methods for calculating the returned stiffness values and, consequently, a high level of agreement in measurement between machines (quantified using the intraclass correlation coefficient [ICC] and Bland-Altman analysis) will allow research findings to be translated to the clinic. This study assessed three locations within the biceps muscle (50% and 75% of the distance between the acromioclavicular joint and antecubital fossa, and superior to distal myotendinous junction [MTJ]) of 32 healthy volunteers with two different machines, the Canon Aplio i600 and SuperSonic Imagine Aixplorer (SSI), to compare the reported shear wave velocities and the variability by coefficient of variation (CV) and ICC. There was no difference in the CV between machines, but a significant difference in the CV at muscle regions, with the 75% location having a 40.2% reduction in CV. The 75% location had the highest ICC values with good posterior mean ICCs of 0.84 on the Canon and 0.83 on the SSI. The 50% and MTJ locations had poor ICC values. The 75% location provided the lowest CV and highest ICC and should be used for future stiffness assessments.

Shear wave elastography combined with electromyography to assess the effect of botulinum toxin on spastic dystonia following stroke: A pilot study

Background

Shear wave elastography (SWE) is a method for carrying out a quantitative assessment of the mechanical properties of soft tissues in terms of stiffness. In stroke survivors, the paretic muscles may develop hypertonia due to both neural-mediated mechanisms and structural alterations with consequent muscular fibrous-fatty remodeling.

Methods

Fourteen adult patients with spastic dystonia following stroke were recruited. Muscle hypertonia was assessed using the modified Ashworth scale (MAS). Muscle activation was measured by surface electromyography (sEMG) with the selected muscle in shortened (spastic dystonia) and stretched (dynamic stretch reflex) positions. SWE was performed on a selected paretic muscle and on the contralateral non-paretic one to calculate shear wave velocities (SWV) along and across muscular fibers. The modified Heckmatt scale (MHS) pattern was also determined. All evaluations were performed shortly before BoNT-A injections (T0) and one month later (T1).

Results

All SWV on paretic muscles were higher than contralateral non-paretic ones (p < 0.01). After BoNT-A injection, a significant reduction in MAS (p = 0.0018), spastic dystonia (p = 0.0043), and longitudinal SWE measurements, both in shortened (p = 0.001) and in stretched muscular conditions (p = 0.0029), was observed. No significant changes in SWV on non-paretic muscles were observed. Higher SWV resulted along the direction of muscular fibers vs. across them (p = 0.001). No changes resulted from the MHS evaluations after BoNT-A. There was a positive correlation between MHS scores and SWV values while the muscle was in the shortened position, but not with spastic dystonia recorded by sEMG.

Conclusions

This is the first study evaluating the effect of BoNT-A on muscle hypertonia following stroke, assessed by both SWE and sEMG. These findings support SWE as a useful method to disclose intrinsic muscular remodeling, independently of the effect of spastic dystonia, in particular, while muscles were assessed in a neutral position. SWE measurements of muscle stiffness cannot tell apart neural-mediated and intrinsic muscle hypertonia. Interestingly, when sEMG activity is very limited, as in spastic muscles kept in a shortened position, SWE can provide a measurement of stiffness due almost completely to intrinsic muscle changes. Alongside sEMG, SWE could aid clinicians in the assessment of responses to treatments.

Viscoelasticity assessment for in vivo quantification of muscle contusion injury in rats using shear wave elastography

The aim of the study described here was to investigate the role of viscoelasticity in assessing muscle fibrosis and inflammation in a rat model of contusion using quantitative shear wave elastography (SWE). Unilateral gastrocnemius muscle contusion was induced in 32 male rats using an impactor apparatus. The contralateral muscles served as the control group. SWE was applied to the control group and rats 1, 3, 14 and 21 d after successful modeling (each time point group, n = 8). Histologic features were used as reference standards. The degree of fibrosis was moderately correlated with shear wave speed (r = 0.53), whereas the degree of inflammation was well correlated with shear wave dispersion (SWD) slope (r = 0.74). The area under the receiver operating characteristic curve (AUC) for the dispersion slope for muscle inflammation and fibrosis assessment was 0.87 (95% confidence interval: 0.705-0.963), which exceeded that of the shear wave speed (0.68, 95% confidence interval: 0.494-0.834). The larger decline in dispersion slope in the fibrotic stage than in the inflammation stage (1-d group vs. 14-d group or 21-d group, p &lt; 0.05) indicated better predictive performance than the shear wave speed.

Shear-Wave Elastography and Viscosity PLUS for the Assessment of Peripheric Muscles in Healthy Subjects: A Pre- and Post-Contraction Study

Viscosity is a novel parameter, recently introduced in the use of elastographic techniques, correlating to shear-wave dispersion. The purpose of this study was to provide normal reference viscosity values for the peripheral muscles in healthy volunteers. This prospective study included 38 subjects who underwent US examinations between November 2021 and January 2022. Measurements were taken on the calf and the deltoid muscles in both pre- and post-contraction states. The age range was 21–29 years, with a median of 26 years. The SWE and ViPLUS values in the deltoid muscles were significantly higher than in the soleus muscles in both pre- and post-contraction sets (p = 0.002). There were statistically significant differences between the pre- and post-contraction values for both the SWE and ViPLUS values in the subgroup analysis. The ICC estimates and the 95% confidence intervals were based on a mean rating (k = 2), an absolute agreement, and a two-way random-effects model, demonstrating excellent agreement between the measurements taken by the two examiners.

SWEmean of Quadriceps, a Potential Index of Complication Evaluation to Patients with Chronic Obstructive Pulmonary Disease

Purpose

To develop a potential quadriceps' index of complication evaluation for patients with chronic obstructive pulmonary disease (COPD) which is simple, convenient, and quantifiable.

Patients and Methods

We conducted a prospective study of 59 patients with COPD and 56 healthy controls recruited by the Chengdu First People's Hospital. Grayscale ultrasound (US) of the rectus femoris was performed to measure thickness (RF_thick) and cross-sectional area (RF_csa). Shear wave elastography was used to determine the mean elasticity index (SWE_mean) of the rectus femoris (SWE_RFmean), vastus lateralis (SWE_VLmean) and vastus medialis (SWE_VMmean). Clinical features included dyspnea index score (modified British Medical Research Council (MMRC) score), COPD Assessment Test (CAT), the Five-Repetition Sit-to-Stand Test (5STS) and the Six-Minute Walk Test (6MWT). We compared the differences between US parameters and SWEmean in healthy controls and COPD patients. We also described the correlation between US parameters, SWE_mean and clinical features of patients with COPD.

Results

The intra-observer repeatability for the performance of using SWE to measure quadriceps stiffness was excellent (intraclass correlation coefficient (ICC)>0.75, p < 0.001). There was a statistically significant difference in the SWE_mean of the quadriceps (p < 0.001), but no significant difference in terms of RF_thic and RF_csa (p > 0.05) between healthy controls and COPD patients. The SWE_RFmean was positively correlated with the 6MWT (r = 0.959, p < 0.001), and negatively related to the mMRC (r=-0.825, p < 0.001), CAT (r=-0.993, p < 0.001) and 5STS (r=-0.936, p < 0.001). However, the RF_thic, RF_csa, SWE_VLmean and SWE_VMmean were not correlated with clinical features (p > 0.05).

Conclusion

As a supplement to US, SWE reflects changes of stiffness in the quadriceps of COPD patients, and can expanding the dimension of US for assessing the quadriceps. Furthermore, SWE_mean was associated with clinical features, and represents a potential index with which to reflect the clinical features of COPD patients.

Changes in stiffness at active myofascial trigger points of the upper trapezius after dry needling in patients with chronic neck pain: a randomized controlled trial

BACKGROUND/OBJECTIVE

Since, to our knowledge, the effects of dry needling (DN) on active myofascial trigger point (MTrP) stiffness have not been analyzed previously with shear wave elastography (SWE), our aim was to compare the effects of a single session of DN and sham DN applied to the most active MTrP located in the upper trapezius muscle on clinical outcomes.

METHODS

A randomized, double-blinded sham-controlled trial was conducted; 60 patients were randomized into an experimental (DN) or sham (sham DN) group. Baseline data including sociodemographic and clinical characteristics were collected. SWE and pain pressure thresholds (PPTs) at the MTrP and a control point located 3 cm laterally were the main outcomes assessed before and 10 min after the interventions.

RESULTS

Patients receiving DN interventions experienced greater increases in the control point PPTs immediately after receiving the intervention compared with sham DN (p < 0.05), but no differences were found for the MTrP (p > 0.05). Post-intervention PPT improvements were found at both locations for both groups (p < 0.01). No significant changes for either MTrP or control locations were found for SWE outcomes in either group (all ps > 0.05). No significant within-group SWE differences were found in the DN or sham DN groups (p > 0.05).

CONCLUSION

A single session of DN or sham DN applied to active MTrPs located in the upper trapezius muscle produced no detectable changes in stiffness at the MTrP or control locations. Real DN induced an immediate analgesic response at both MTrP and control locations, while sham DN induced an immediate MTrP response.

TRIAL REGISTRATION NUMBER

NCT04832074 (ClinicalTrials.gov).

Assessment of ultrasound shear wave elastography within muscles using different region of interest sizes, manufacturers, probes and acquisition angles: an ex vivo study

BACKGROUND

The application of shear wave elastography (SWE) in assessment of the musculoskeletal system is affected by various factors. This study aimed to explore the influence of machines, probes, region of interest (ROI) sizes, and the acquisition angles on muscle shear wave speed (SWS).

METHODS

The SWS of ex vivo isolated muscles were acquired using 3 different machines (Aixplorer system, SuperSonic Imagine; Acuson S3000, Siemens Healthcare; Resona 7, Mindray) and 2 linear probes (Aixplorer system, SL 10-2 and SL 15-4). Also, 4 different ROI sizes (diameter 1-10 mm) and 9 different acquisition angles (0-40°) were tested. The SWS acquired under different conditions were compared, and the intra-class correlation coefficients (ICC) were used to evaluate reproducibility.

RESULTS

There was a significant difference in SWS acquired using the 3 different machines (P<0.001) or with 9 different angles (P=0.008). There was no significant difference in SWS acquired using 2 probes (P=0.053) or 4 different ROI sizes (P=0.874, 0.778, and 0.865 for 3 operators, respectively). All machines produced substantial intra-system reproducibility (ICC, 0.61-0.80). Both probes demonstrated an almost perfect degree of intra-system agreement (ICC, >0.80), and nearly all ROI sizes demonstrated an almost perfect degree of intra- and inter-operator agreement (ICC, >0.80). The measurement reliability was higher when the acquisition angles were no more than 20°.

CONCLUSIONS

The 3 machines had different SWS values. Attention should be paid when comparing SWS results using different machines. For the Aixplorer system, the ROI size had no effect on the SWS values. Angles larger than 25° will lead to SWS measurements with greater variability compared to smaller angles (≤20°).

Increased Stiffness of the Superficial Cervical Extensor Muscles in Patients With Cervicogenic Headache: A Study Using Shear Wave Elastography

Background

Cervicogenic headache (CEH) is a secondary headache caused by lesions of the cervical spine and surrounding soft tissues. Cervical muscle dysfunction may be related to the onset of CEH. However, whether cervical muscle stiffness changes in patients with CEH has not been well studied. The purpose of this study was to explore changes in superficial cervical extensor muscle stiffness in patients with CEH using shear wave elastography (SWE).

Methods

In this study, 19 patients with CEH and 20 healthy controls were recruited. Superficial cervical extensor muscle stiffness was obtained from SWE, and the SuperLinear SL10-2 MHz linear array probe in the musculoskeletal muscle mode was chosen as the transducer. Regions of interest in the trapezius (TRAP), splenius capitis (SPL), semispinalis capitis (SCap), and semispinalis cervicis (SCer) were manually segmented. Correlations between superficial cervical extensor muscle stiffness and visual analog scale (VAS) scores, age, and body mass index (BMI) were analyzed using Pearson's correlation. Receiver operating characteristic (ROC) curve was used to investigate the diagnostic ability of superficial cervical extensor stiffness for CEH.

Results

Superficial cervical extensor muscle stiffness on the headache side of patients with CEH was higher than that on the non-headache side and in healthy controls (p < 0.05). Increased stiffness was also observed in SCer on the non-headache side of patients with CEH compared to healthy controls (p < 0.01). In patients with CEH, SCer stiffness was positively correlated with VAS scores (r = 0.481, p = 0.037), but no correlation was found between other muscles and VAS scores (p > 0.05). The areas under the curve of TRAP, SPL, SCap, and SCer in diagnosing CEH were 0.766, 0.759, 0.964, and 1.000, respectively.

Conclusions

Increased stiffness was observed in the superficial cervical extensor muscles on the headache side of patients with CEH. SCer stiffness was correlated with headache intensity in patients with CEH and may provide clues for the diagnosis of CEH.

Arterial Stiffness Assessment in Healthy Participants Using Shear Wave Elastography

BACKGROUND

Arterial stiffness is an important biomarker for cardiovascular disease. Shear wave elastography (SWE) provides quantitative estimates of tissue stiffness.

OBJECTIVE

This study aimed to provide reference values for arterial wall, assessing the suitability of SWE to quantify elasticity of the common carotid artery (CCA) and evaluating inter- and intra-observer reproducibility.

METHODS

A Supersonic Aixplorer ultrasound system with L15-4 probe was used to scan longitudinal sections of the CCA. Young's modulus (YM) was measured within 2-mm regions of interest. Reproducibility was assessed within a subgroup of 16 participants by two operators (one novice and one experienced) during two sessions >one week apart.

RESULTS

This study involves seventy-three participants with a mean age of 40±10 years and body mass index of 26 ±6 kg/m2. YM estimates were 59 kPa ±19 in men and 56 kPa ±12 in women. The average YM of the CCA walls was 58 kPa ±15 (57 ±15 kPa for the anterior wall and 58 ±20 kPa for the posterior wall, p=0.75). There was no significant difference in the mean of YM estimates of the CCA between the observers (observer: one 51 ±14 kPa and observer two: 55 ±17 kPa [p=0.46]). inter- and intra-observer reproducibility was fair to good (Intra-class correlations, ranging from 0.46 to 0.71). Inter-frame variability was 28%.

CONCLUSION

In healthy individuals, SWE provided an estimate of YM of the CCA (58 kPa) with fair to good reproducibility. This study demonstrated the potential of using SWE for assessing biomechanical properties of blood vessels.

Visualization of Human Skeletal Muscle Anisotropy by Using Dual-Direction Shear Wave Imaging

OBJECTIVE

Ultrasound (US) shear wave elasticity imaging (SWEI) is a mature technique for diagnosing the elasticity of isotropic tissues. However, the elasticity of anisotropic tissues, such as muscle and tendon, cannot be diagnosed correctly using SWEI because the shear wave velocity (SWV) varies with tissue fiber orientations. Recently, SWEI has been studied for measuring the anisotropic properties of muscles by rotating the transducer; however, this is difficult for clinical practice.

METHODS

In this study, a novel dual-direction shear wave imaging (DDSWI) technique was proposed for visualizing the mechanical anisotropy of muscles without rotation. Longitudinal and transverse shear waves were created by a specially designed external vibrator and supersonic pushing beam, respectively; the SWVs were then tracked using ultrafast US imaging. Subsequently, the SWV maps of two directions were obtained at the same scanning cross section, and the mechanical anisotropy was represented as the ratio between them at each pixel.

RESULTS

The performance of DDSWI was verified using a standard phantom, and human experiments were performed on the gastrocnemius and biceps brachii. Experimental results of phantom revealed DDSWI exhibited a high precision of <0.81 % and a low bias of <3.88 % in SWV measurements. The distribution of anisotropic properties in muscle was visualized with the anisotropic ratios of 1.54 and 2.27 for the gastrocnemius and biceps brachii, respectively.

CONCLUSION

The results highlight the potential of this novel anisotropic imaging in clinical applications because the conditions of musculoskeletal fiber orientation can be easily and accurately evaluated in real time by DDSWI.

In Hamstring Muscles of Patients With Knee Osteoarthritis an Increased Ultrasound Shear Modulus Indicates a Permanently Elevated Muscle Tonus

Background

Some patients with knee osteoarthritis (KOA) show pain, stiffness and limited flexion and extension at the back of the knee, leading to dysfunction and affecting life. This may be related to changes in the biomechanical properties of skeletal muscles. Shear wave elastography (SWE) can detect these changes by measuring muscle shear modulus.

Aims

To investigate hamstring muscle shear modulus of healthy people and patients was studied using SWE method, and the correlation analysis between the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score of patients’ subjective feeling and shear modulus of objective quantification was conducted.

Methods

The hamstring shear modulus was measured by SWE in 50 patients and 50 healthy individuals. Pearson correlation coefficient was used to evaluate the correlation between hamstring stiffness and shear modulus in patients.

Results

The hamstring shear modulus were significantly higher in the KOA group [the semimembranosus (SM) 15.23 ± 7.23, the semitendinosus (ST) 15.94 ± 5.40, the biceps femoris long tendinitis (BFL) 14.21 ± 6.55] than in the control group (the SM 10.95 ± 2.41, the ST 11.25 ± 2.23, the BFL 9.98 ± 2.81) (p = 0.000, p = 0.000, p = 0.001). The hamstring shear modulus in the KOA group was moderately positively correlated with pain, shear modulus, and physical function score.

Conclusion

Preliminary results show that the shear modulus of the hamstring of KOA patients is higher than that of healthy people, the WOMAC score and the shear modulus of patients are moderately correlated. These preliminary results show that ultrasonic shear wave elastography measurement of shear modulus may be enough to sensitive, can detect these effects, more targeted in order to assist the doctor’s diagnosis and treatment.

Ultrasonic Elastography of the Rectus Femoris, a Potential Tool to Predict Sarcopenia in Patients With Chronic Obstructive Pulmonary Disease

Purpose: Skeletal muscle dysfunction is common in patients with chronic obstructive pulmonary disease (COPD) and is associated with a poor prognosis. Abnormal muscle quantity of the lower limbs is a manifestation of skeletal muscle dysfunction in patients with COPD. Shear wave ultrasound elastography (SWE) is a novel and possible tool to evaluate qualitative muscle parameters. This study explores the feasibility of SWE to measure the stiffness of the rectus femoris and evaluates its value in predicting sarcopenia in patients with COPD.

Methods: Ultrasound examination of the rectus femoris was performed to determine the mean elasticity index (SWE_mean), cross-sectional area (RF_csa), and thickness (RF_thick) using grayscale ultrasonography (US) and SWE in 53 patients with COPD and 23 age-matched non-COPD healthy controls. The serum levels of circulating biomarkers (GDF15, resistin, and TNF-α) were measured using ELISA. The definition of sarcopenia followed the guidelines from the Asian Working Group for Sarcopenia. Receiver operating characteristic (ROC) curve analysis of the SWE_mean, RF_thick, and RF_csa was used to evaluate their predictive ability for sarcopenia.

Results: The intraobserver and interobserver repeatability of SWE performance was excellent (all correlation coefficients > 0.95; p < 0.05). The SWE_mean of the rectus femoris in patients with COPD (8.98 ± 3.12 kPa) was decreased compared with that in healthy controls (17.00 ± 5.14 kPa) and decreased with advanced global initiative for chronic obstructive lung disease (GOLD) stage. Furthermore, SWE_mean was found to be independent of sex, height, and body mass, and a lower SWE_mean in patients with COPD was positively associated with reduced pulmonary function, worse physical function, poor exercise tolerance, decreased muscle strength, and worse dyspnea index score. The correlation between physical function [five-repetition sit-to-stand test (5STST)], muscle function, and SWE_mean was higher than those of RF_thick and RF_csa. In addition, SWE_mean was negatively correlated with serum GDF15 levels (r = −0.472, p < 0.001), serum resistin levels (r = −0.291, p = 0.035), and serum TNF-α levels (r = −0.433, p = 0.001). Finally, the predictive power of SWE_mean [area under the curve (AUC): 0.863] in the diagnosis of sarcopenia was higher than that of RF_thick (AUC: 0.802) and RF_csa (AUC: 0.816).

Conclusion: Compared with grayscale US, SWE was not affected by the patient’s height, weight, or BMI and better represented skeletal muscle function and physical function. Furthermore, SWE is a promising potential tool to predict sarcopenia in patients with COPD.

Full Characterization of in vivo Muscle as an Elastic, Incompressible, Transversely Isotropic Material Using Ultrasonic Rotational 3D Shear Wave Elasticity Imaging

Using a 3D rotational shear wave elasticity imaging (SWEI) setup, 3D shear wave data were acquired in the vastus lateralis of a healthy volunteer. The innate tilt between the transducer face and the muscle fibers results in the excitation of multiple shear wave modes, allowing for more complete characterization of muscle as an elastic, incompressible, transversely isotropic (ITI) material. The ability to measure both the shear vertical (SV) and shear horizontal (SH) wave speed allows for measurement of three independent parameters needed for full ITI material characterization: the longitudinal shear modulus μL , the transverse shear modulus μT , and the tensile anisotropy χE . Herein we develop and validate methodology to estimate these parameters and measure them in vivo, with μL = 5.77±1.00 kPa, μT = 1.93±0.41 kPa (giving shear anisotropy χμ = 2.11±0.92 ), and χE = 4.67±1.40 in a relaxed vastus lateralis muscle. We also demonstrate that 3D SWEI can be used to more accurately characterize muscle mechanical properties as compared to 2D SWEI.

Measuring and Modelling Nonlinear Elasticity of Ex Vivo Mouse Muscles

Elastography is a noninvasive imaging technique that provides information on soft tissue stiffness. Young's modulus is typically used to characterize soft tissues' response to the applied force, as soft tissues are often considered linear elastic, isotropic, and quasi-incompressible materials. This approximation is reasonable for small strains, but soft tissues undergo large deformations also for small values of force and exhibit nonlinear elastic behavior. Outside the linear regime, the elastic modulus is dependent on the strain level and is different for any kind of tissue. The aim of this study was to characterize, ex vivo, the mechanical response of two different mice muscles to an external force. A system for transverse force-controlled uniaxial compression enabled obtaining the stress-strain (σ-ε) curve of the samples. The strain-dependent Young's modulus (SYM) model was adopted to reproduce muscle compression behavior and to predict the elastic modulus for large deformations. After that, a recursive linear model was employed to identify the initial linear region of the σ-ε curve. Results showed that both muscle types exhibited a strain hardening effect and that the SYM model provided good fitting of the entire σ-ε curves. The application of the recursive linear model allowed capturing the initial linear region in which the approximation of these tissues as linear elastic materials is reasonable. The residual analysis displayed that even if the SYM model better summarizes the muscle behavior on the entire region, the linear model is more precise when considering only the initial part of the σ-ε curve.

Quantifying Lower Limb Muscle Stiffness as Ambulation Function Declines in Duchenne Muscular Dystrophy with Acoustic Radiation Force Impulse Shear Wave Elastography

Duchenne muscular dystrophy (DMD) is a progressive muscular disease, but validated imaging tools to quantify muscle microstructure alteration as mobility declines are lacking. We aimed to determine the feasibility of using acoustic radiation force impulse shear-wave elastography (ARFI/SWE) in the quantitative assessment of lower limb muscle stiffness in DMD patients. Shear wave velocities (SWVs) of lower limbs were measured in 39 DMD patients and 36 healthy controls aged 3-20 y. Mean SWV values of the controls and of the DMD patients at different ambulatory stages were compared using analysis of variance with Bonferroni correction. The DMD group had increased lower limb muscle stiffness compared with controls. Stiffness of the tibialis anterior and medial gastrocnemius muscle decreased from ambulatory to early non-ambulatory stages, whereas stiffness of the rectus femoris muscle increased from ambulatory to late non-ambulatory stages. We describe how SWV changes in lower limb muscles have the potential to predict ambulatory decline in DMD.

A Novel Elastography Phantom Prototype for Assessment of Ultrasound Elastography Imaging Performance

The aims of this study were firstly to manufacture and evaluate a novel elastography test phantom and secondly to assess the performance of an elastography system using this phantom. A novel Leicester-St. Thomas' Elastography Pipe (L-STEP) test phantom consisting of five soft polyvinyl acrylic-cryogel pipes of varying diameters (2-12 mm), embedded at 45° within an agar-based tissue-mimicking material was developed. A shear-wave elastography (SWE) scanner was used by two blinded operators to image and assess longitudinal sections of the pipes. Young's modulus estimates were dependent on the diameter of pipes and at superficial depths were greater than deeper depths (mean 98 kPa vs. 59 kPa) and had lower coefficients of variation (mean 21% vs. 53%). The penetration depth (maximum depth at which a SWE signal was obtained) increased with increasing pipe diameter. Penetration depth measurements had excellent inter- and intra-operator reproducibility (intra-class correlation coefficients >0.8) and coefficient of variation range of 2%-12%. A new metric, called the summative performance index, was defined as the sum of the ratios of the penetration depth/pipe diameter. The L-STEP phantom is suitable for assessing key aspects of elastography imaging performance: resolution, accuracy, reproducibility, depth dependence, sensitivity and our novel summative performance index.

Is Shear-Wave Elastography a Clinical Severity Indicator of Myofascial Pain Syndrome? An Observational Study

Since manual palpation is a subjective procedure for identifying and differentiate Myofascial Trigger Points -MTrPs-, the use of Shear Wave Elastography -SWE- as an objective alternative is increasing. This study aimed to analyze pain pressure thresholds -PPTs- and SWE differences between active MTrPs, latent MTrPs and control points located in the upper trapezius to analyze the association of SWE features with clinical severity indicators (e.g., pain extension area, PPTs, neck pain and neck disability). An observational study was conducted to calculate the correlation and to analyze the differences of sociodemographic, clinical and SWE features on 34 asymptomatic subjects with latent MTrPs and 19 patients with neck pain and active MTrPs. Significant PPT differences between active with latent MTrPs (p < 0.001) and control points (p < 0.001) were found, but no differences between latent MTrPs and control points (p > 0.05). No stiffness differences were found between active MTrPs with latent MTrPs or control points (p > 0.05). However, significant control point stiffness differences between-samples were found (p < 0.05). SWE showed no significant correlation with clinical severity indicators (p > 0.05). No stiffness differences between active and latent MTrPs were found. Neck pain patients showed increased control point stiffness compared with asymptomatic subjects. SWE showed no association with clinical severity indicators.

Quantitative assessment of normal middle deltoid muscle elasticity at various arm abduction using ultrasound shear wave elastography

The objective of this study is to assess the change in the normal MD elasticity using shear wave elastography (SWE) through measuring the middle deltoid (MD) elasticity in healthy participants at various arm abduction (with bilateral arms at 0 degrees abduction and 90 degrees active abduction) and analyzing the factors affecting normal MD elasticity. Mean shear wave velocity (SWV) of the MD in healthy right-handed participants were evaluated using SWE at different arm abduction, and potential factors (gender, MD thickness, age, body mass index) affecting MD elasticity were analyzed. Different arm abduction positions of each participant were as follows: (i) 0° abduction of bilateral arm (L0° and R0°), (ii) 90° active abduction of bilateral arm (L90° and R90°). Mean SWV was significantly higher at L90° than L0°, higher at R90° than R0°, higher at R0° than L0°, and higher at R90° than L90° (all P < 0.0001). SWV was significantly higher in males at both L0° (P < 0.05) and R0° (P < 0.01) than in females. Neither MD thickness, age nor body mass index influenced MD elasticity. Reference ranges of normal MD elasticity were 2.4–3.1 m/s in males and 2.2–2.9 m/s in females at L0° and 2.5–3.3 m/s in males and 2.4–3.2 m/s in females at R0°, and were 4.9–6.7 m/s at L90°, 5.2–7.1 m/s at R90° for both males and females. SWE is a feasible technique to assess normal MD elasticity at various arm abduction. Our results suggest that normal MD elasticity at L0°, R0°, L90°, and R90° with SWE are different. Moreover, these reference ranges may serve as quantitative baseline measurements for assessment of normal MD elasticity in the future.

Effect of autogenous crack self-healing on mechanical strength recovery of cement mortar under various environmental exposure

While research on self-healing of cement-based materials has recently gained considerable attention and made sizable progress, there is still ongoing debate and controversy regarding the effect of crack closing induced by autogenous self-healing on mechanical strength recovery. Despite that several techniques have been used to capture and quantify the self-healing of surface cracks, the resulting effect on mechanical strength has not, to date, been explored and quantified in a rigorous and systematic manner. Therefore, in this study, a broad array of multi-scale techniques including non-destructive shear wave velocity, high-resolution X-ray computed tomography (µCT), and 3D image analysis was deployed to examine the effects of autogenous crack self-healing on the mechanical strength recovery in various mortar specimens. The influence of microstructural changes induced by additives such as swelling compounds, silica-based additions, and carbonating minerals on strength recovery under diverse environmental exposures was further explored. The results capture the relationship between the crack closing mechanism imparted by self-healing and mechanical strength recovery, therefore elucidating the discrepancies in mechanical strength recovery results reported in the open literature.

Reliability of Sonoelastography Measurement of Tongue Muscles and Its Application on Obstructive Sleep Apnea

Few studies have explored the feasibility of shear-wave ultrasound elastography (SWUE) for evaluating the upper airways of patients with obstructive sleep apnea (OSA). This study aimed to establish a reliable SWUE protocol for evaluating tongue muscle elasticity and its feasibility and utility in differentiating patients with OSA. Inter-rater and intra-rater reliability of SWUE measurements were tested using the intraclass correlation coefficients. Submental ultrasound was used to measure tongue thickness and stiffness. Association between the ultrasound measurements and presence of OSA was analyzed using multivariate logistic regression. One-way analysis of variance was used to examine if the values of the ultrasound parameters varied among patients with different severities of OSA. Overall, 37 healthy subjects and 32 patients with OSA were recruited. The intraclass correlation coefficients of intra‐ and inter-rater reliability for SWUE for tongue stiffness ranged from 0.84 to 0.90. After adjusting for age, sex, neck circumference, and body mass index, the risk for OSA was positively associated with tongue thickness [odds ratio 1.16 (95% confidence interval 1.01–1.32)] and negatively associated with coronal imaging of tongue muscle stiffness [odds ratio 0.72 (95% confidence interval 0.54–0.95)]. There were no significant differences in tongue stiffness among OSA patients with varying disease severity. SWUE provided a reliable evaluation of tongue muscle stiffness, which appeared to be softer in patients with OSA. Future longitudinal studies are necessary to investigate the relationship between tongue softening and OSA, as well as response to treatment.

Quantification of immobilization-induced changes in human calf muscle using speed-of-sound ultrasound: An observational pilot study

Short-term immobilization leads to fatty muscular degeneration, which is associated with various negative health effects. Based on literature showing very high correlations between MRI Dixon fat fraction and Speed-of-Sound (SoS), we hypothesized that we can detect short-term-immobilization-induced differences in SoS.Both calves of 10 patients with a calf cast on one side for a mean duration of 41 ± 26 days were examined in relaxed position using a standard ultrasound machine. Calf perimeters were measured for both sides. A flat Plexiglas-reflector, placed vertically on the opposite side of the probe with the calf in-between, was used as a timing reference for SoS. SoS was both manually annotated by two readers and assessed by an automatic annotation algorithm. The thickness values of the subcutaneous fat and muscle layers were manually read from the B-mode images. Differences between the cast and non-cast calves were calculated with a paired t test. Correlation analysis of SoS and calf perimeter was performed using Pearson's correlation coefficient.Paired t test showed significant differences between the cast and non-cast side for both SoS (P < .01) and leg perimeter (P < .001). SoS was reduced with the number of days after cast installment (r = -0.553, P = .097). No significant differences were found for muscle layer thickness, subcutaneous fat layer thickness, mean fat echo intensity, or mean muscle echo intensity.Short-term-immobilization led to a significant reduction in SoS in the cast calf compared to the healthy calf, indicating a potential role of SoS as a biomarker in detecting immobilization-induced fatty muscular degeneration not visible on B-mode ultrasound.

Ultrasound Elastographic Measurement of Rigor Mortis in an Animal Model: A Feasibility Study for Improved Time-of-Death Estimates in Forensic Investigations

OBJECTIVE. The purpose of our study was to assess the feasibility of 2D shear wave ultrasound elastography to quantitatively measure changes of rigor mortis. SUBJECTS AND METHODS. Muscle stiffness of two live pigs and nine sacrificed pigs was measured in kilopascals using ultrasound elastography. The nine sacrificed pigs were divided into three groups of three pigs each and placed in one of three environments at 90°F (32°C), 70°F (21°C), or 34°F (1°C). Ultrasound elastography of five muscles was performed at 1- to 2-hour intervals for up to 50 hours postmortem. For each pig and muscle location, the time to start, peak intensity, duration of peak, and time to decline of rigor mortis were identified from the graphs of muscle stiffness values over time. These outcome variables were then compared across ambient temperature, body weight, and age groups using the Wilcoxon rank sum test. RESULTS. Postmortem measurements show a rise, peak, and decline of muscle stiffness after death. Rigor mortis was highly significantly affected by ambient temperature (p < .001), was significantly affected by body weight (p = .04), and was not significantly affected by animal age or muscle location (facial vs truncal vs limb) (p > .50). Peak intensity of rigor mortis developed more quickly but attained lower levels of muscle stiffness at 90°F (80-100 kPa) compared with 70°F and 34°F (280-300 kPa) (p < .001). The duration of peak rigor mortis and the time to decline of rigor mortis were significantly longer for the lower temperatures (p < .001). CONCLUSION. Two-dimensional shear wave ultrasound elastography can quantifi-ably measure the trajectory of rigor mortis in an animal model. This new approach may have direct implications for human forensic investigations.

Use of Shear Wave Elastography for Quantitative Assessment of Muscle Stiffness After Botulinum Toxin Injection in Children With Cerebral Palsy

OBJECTIVES

This study aimed to investigate the stiffness of the gastrocnemius (GC) muscle with acoustic radiation force impulse (ARFI) elastography after botulinum toxin-A (BTX-A) injection in children with spastic cerebral palsy (CP) and to examine the relationship between elastographic and clinical parameters.

METHODS

This prospective randomized single-blind controlled clinical study included 49 lower extremities of 33 children with spastic CP. They were randomized into 2 groups: group 1 (n = 25 extremities in 17 children) received BTX-A injection and a home-based exercise program; group 2 (n = 24 extremities in 16 children) received only a home-based exercise program. Patients were evaluated in pretreatment and posttreatment periods in the first and third months with ARFI elastography, the Modified Ashworth Scale, Modified Tardieu Scale, Pediatric Functional Independence Measure, Gross Motor Function Classification System, and goniometric range of motion measurement of the ankle.

RESULTS

A statistically significant difference was found in elastography of the GC muscle in group 1 only at the first month after treatment (P < .05). No statistical difference was found in elastography of the GC after treatment in group 2. According to the Modified Ashworth Scale, Modified Tardieu Scale, and ankle passive range of motion, group 1 showed significant improvements after treatment (P < .05). Also, there was a significant correlation between these clinical parameters and elastographic measurements (P < .05).

CONCLUSIONS

According to the results of this study, the measurements from ARFI elastography combined with clinical parameters might be useful for evaluation of spasticity after BTX-A treatment in children with CP. Also, they might be useful in distinguishing patients who will benefit clinically, especially in the early stages of treatment.

Usability and Pitfalls of Shear-Wave Elastography for Evaluation of Muscle Quality and Its Potential in Assessing Sarcopenia: A Review

Sarcopenia is age-related progressive and generalized loss of skeletal muscle mass and strength. Its prevalence is rising, which poses a burden for society because it increases disability and dependency and therefore raises health care costs. Muscle mass quality, however-an essential part of sarcopenia-is not easily diagnosable yet. Recent interest has risen for ultrasonographic evaluation of muscle. This review introduces muscle elastography as a possible, easy and cheap tool to evaluate qualitative muscle parameters. Basic principles of muscle elastography are described, as well as different elastography techniques and some technical considerations. Furthermore, a proposal for practical guidelines is offered and factors influencing muscle stiffness are highlighted.

Determination of reference ranges for normal upper trapezius elasticity during different shoulder abduction using shear wave elastography: a preliminary study

The purpose of this study was to determine the reference ranges of normal upper trapezius (UT) elasticity during different shoulder abduction using shear wave elastography (SWE). Mean shear wave velocity (SWV) of UT elasticity in eighty healthy participants were measured at left and right shoulder 0° abduction and 90° passive abduction (L0°, R0°, L90°, R90°) with SWE. The effects of potential factors (gender, UT thickness, age, and body mass index) on UT elasticity were analyzed. The reference ranges of normal UT elasticity were calculated by using the normal distribution method. UT elasticity was significantly different among various shoulder abduction (P < 0.0001). UT elasticity was significantly higher in males at both L90° (P < 0.05) and R90° (P < 0.01) than in females. The reference ranges of normal UT elasticity were 2.90-4.01 m/s at L0° and 3.01-4.29 m/s at R0°, and were 4.90-6.40 m/s in males and 4.40-6.20 m/s in females at L90°, 5.20-7.02 m/s in males and 4.71-6.80 m/s in females at R90°. Our results suggest that gender should be considered when determining the reference ranges of normal UT elasticity at L90° and R90° with SWE. These values may provide quantitative baseline measurements for the assessment of UT muscle strain in the future.

Ultrasound Shear Wave Elastography to Assess Tissue Mechanical Properties in Somatic Dysfunction: A Feasibility Study

CONTEXT

Diagnosis of somatic dysfunction is based on subjective palpatory osteopathic assessments. This subjectivity has posed a challenge for researchers in studying osteopathic medicine. The development and use of radiological imaging techniques to objectively confirm or quantify muscle tissue stiffness associated with somatic dysfunction could be of benefit in osteopathic clinical practice, training, and further research.

OBJECTIVES

To investigate the feasibility of ultrasound shear wave elastography (SWE) to quantify muscle tissue stiffness in somatic dysfunction before and after osteopathic manipulative treatment (OMT).

METHODS

In this prospective study, we assessed lumbar spine somatic dysfunction in 20 adult patients before and after a single OMT session using standard osteopathic palpatory assessments by osteopathic physician faculty members in the Department of Osteopathic Principle and Practice at Rocky Vista University College of Osteopathic Medicine (Utah campus). Shear wave velocity (SWV, m/s) was measured in lumbar paraspinal muscle tissue using a commercial ultrasonography scanner on all participants immediately before and after OMT. In this study, OMT techniques targeted the iliocostalis lumborum and included the articulatory technique, balanced ligamentous tension, facilitated positional release, high-velocity, low-amplitude technique, muscle energy, myofascial release, and the Still technique at the discretion of the osteopathic physician. The difference in SWV between muscle tissues with and without dysfunction, and differences in SWV of dysfunctional tissue before and after OMT were examined using unpaired and paired t tests, as appropriate. The correlation between SWV measurements and osteopathic assessments was examined by the Spearman rank correlation. Intra- and interobserver reliability was analyzed using intraclass correlation coefficient.

RESULTS

The difference in SWV between muscle tissues with and without somatic dysfunction was significant before OMT (mean [SD], 1.93 [0.44] vs 1.69 [0.19]; P=.03) and was not significant after OMT (mean [SD], 1.69 [0.19] vs 1.53 [0.31]; P=.05). The difference in SWV in the same tissue with somatic dysfunction before and after OMT was significant (mean [SD], 1.93 [0.44] vs 1.52 [0.3]; P<.001). The SWV value highly correlated with manual osteopathic assessments (r=0.72). Intra- and interobserver reliability for performing SWE in somatic dysfunction was good (intraclass correlation coefficient >0.80).

CONCLUSIONS

The results of this study show that ultrasound SWE can objectively assess muscle tissue stiffness for diagnosis of somatic dysfunctions and for muscle tissue stiffness changes after OMT.

Effect of acquisition depth and precompression from probe and couplant on shear wave elastography in soft tissue: an in vitro and in vivo study

Background

Shear wave elastography is a promising method to diagnose early musculoskeletal lesions. We aimed to explore the feasible depth and acceptable precompression applied by probe and couplant for soft tissues in the present system.

Methods

Ex-vivo muscles were evaluated at depths of 0.5-6 cm by 3 operators, using 1-5 mm couplant thickness and 0-3.0 kPa probe pressure. We compared the shear wave speed (SWS) and used intraclass correlation coefficients to assess reproducibility. In vivo skin and subcutaneous superficial fascia from volunteers were tested at depths ranging from 0.1-0.5 cm with 1-20 mm couplant thickness.

Results

The SWS of ex-vivo muscles varied and increased with depth, and could not be acquired at 6 cm because the shear wave failed to be detected. Furthermore, while the SWS of ex-vivo muscles were not affected by the couplant thickness, it was affected by probe pressure. Most cases demonstrated a satisfactory agreement degree of the intraoperator reproducibility (ICC, 0.81-0.95) and a substantial interoperator reproducibility (ICC >0.60). Inter- and intra-operator reproducibility was better at a depth of 0.5-4 cm than at 5 cm. In the in vivo study, when tissues within a 0.2 cm depth were evaluated, the SWS that was acquired using a couplant thickness of >10 mm was different from that acquired using other thicknesses.

Conclusions

The SWS acquired at a depth of ≤3 cm with a suitable amount of couplant is recommended.

Shearwave Elastography in the Differentiation of Carpal Tunnel Syndrome Severity

BACKGROUND

There is emerging evidence that ultrasound elastography may provide additional diagnostic information in peripheral neuropathies.

OBJECTIVE

To investigate the use of ultrasound elastography to evaluate median nerve stiffness in patients with carpal tunnel syndrome (CTS), as well as the relationship between the elastographic stiffness and electrophysiological severity.

DESIGN

Case control study.

SETTING

Tertiary hospital outpatient neurophysiology clinic.

PARTICIPANTS

Twenty eight patients (47 wrists) with CTS and 25 control patients (25 wrists).

INTERVENTIONS

None.

MAIN OUTCOME MEAURES

Ultrasound parameters (median nerve cross-sectional area [CSA] at carpal tunnel, ratio of median nerve CSA at carpal tunnel and forearm), shearwave elastography parameter (median nerve stiffness), and electrophysiological severity of carpal tunnel syndrome.

RESULTS

In patients with CTS, median nerve stiffness by ultrasound elastography was increased between the different severity groups (control 83.5 ± 24.8, EDx negative CTS 84.2 ± 46.4, mild 117.7 ± 79.3, moderate 144.0 ± 71.1, severe 196.6 ± 48.4). The control versus moderate and severe subgroup was statistically significant.

CONCLUSIONS

In total, this study has demonstrated that ultrasound elastography was able to discriminate the severity of CTS whereas conventional ultrasound parameters did not.

Real-time shear wave ultrasound elastography: a new tool for the evaluation of diaphragm and limb muscle stiffness in critically ill patients

BACKGROUND

Muscle weakness following critical illness is the consequence of loss of muscle mass and alteration of muscle quality. It is associated with long-term disability. Ultrasonography is a reliable tool to quantify muscle mass, but studies that evaluate muscle quality at the critically ill bedside are lacking. Shear wave ultrasound elastography (SWE) provides spatial representation of soft tissue stiffness and measures of muscle quality. The reliability and reproducibility of SWE in critically ill patients has never been evaluated.

METHODS

Two operators tested in healthy controls and in critically ill patients the intra- and inter-operator reliability of the SWE using transversal and longitudinal views of the diaphragm and limb muscles. Reliability was calculated using the intra-class correlation coefficient and a bootstrap sampling method assessed their consistency.

RESULTS

We collected 560 images. Longitudinal views of the diaphragm (ICC 0.83 [0.50-0.94]), the biceps brachii (ICC 0.88 [0.67-0.96]) and the rectus femoris (ICC 0.76 [0.34-0.91]) were the most reliable views in a training set of healthy controls. Intra-class correlation coefficient for inter-operator reproducibility and intra-operator reliability was above 0.9 for all muscles in a validation set of healthy controls. In critically ill patients, inter-operator reproducibility and intra-operator 1 and 2 reliability ICCs were respectively 0.92 [0.71-0.98], 0.93 [0.82-0.98] and 0.92 [0.81-0.98] for the diaphragm; 0.96 [0.86-0.99], 0.98 [0.94-0.99] and 0.99 [0.96-1] for the biceps brachii and 0.91 [0.51-0.98], 0.97 [0.93-0.99] and 0.99 [0.97-1] for the rectus femoris. The probability to reach intra-class correlation coefficient greater than 0.8 in a 10,000 bootstrap sampling for inter-operator reproducibility was respectively 81%, 84% and 78% for the diaphragm, the biceps brachii and the rectus femoris respectively.

CONCLUSIONS

SWE is a reliable technique to evaluate limb muscles and the diaphragm in both healthy controls and in critically ill patients.

TRIAL REGISTRATION

The study was registered (ClinicalTrial NCT03550222).