An investigation into the variability between different shear wave elastography systems in muscle

Is musculoskeletal pain associated with increased muscle stiffness? Evidence map and critical appraisal of muscle measurements using shear wave elastography

INTRODUCTION AND AIMS

Approximately 21% of the world's population suffers from musculoskeletal conditions, often associated with sensations of stiff muscles. Targeted therapy requires knowing whether typically involved muscles are objectively stiffer compared to asymptomatic individuals. Muscle stiffness is quantified using ultrasound shear wave elastography (SWE). Publications on SWE-based comparisons of muscle stiffness between individuals with and without musculoskeletal pain are increasing rapidly. This work reviewed and mapped the existing evidence regarding objectively measured muscle stiffness in musculoskeletal pain conditions and surveyed current methods of applying SWE to measure muscle stiffness.

METHODS

A systematic search was conducted in PubMed and CINAHL using the keywords "muscle stiffness", "shear wave elastography", "pain", "asymptomatic controls" and synonyms. The search was supplemented by a hand search using Google Scholar. Included articles were critically appraised with the AXIS tool, supplemented by items related to SWE methods. Results were visually mapped and narratively described.

RESULTS

Thirty of 137 identified articles were included. High-quality evidence was missing. The results comprise studies reporting lower stiffness in symptomatic participants, no differences between groups and higher stiffness in symptomatic individuals. Results differed between pain conditions and muscles, and also between studies that examined the same muscle(s) and pathology. The methods of the application of SWE were inconsistent and the reporting was often incomplete.

CONCLUSIONS

Existing evidence regarding the objective stiffness of muscles in musculoskeletal pain conditions is conflicting. Methodological differences may explain most of the inconsistencies between findings. Methodological standards for SWE measurements of muscles are urgently required.

Ultrasonic surface acoustic wave elastography: A review of basic theories, technical developments, and medical applications

Physiological and pathological changes in tissues often cause changes in tissue mechanical properties, making tissue elastography an effective modality in medical imaging. Among the existing elastography methods, ultrasound elastography is of great interest due to the inherent advantages of ultrasound imaging technology, such as low cost, portability, safety, and wide availability. However, most current ultrasound elastography methods are based on the bulk shear wave; they can image deep tissues but cannot image superficial tissues. To address this challenge, ultrasonic elastography methods based on surface acoustic waves have been proposed. In this paper, we present a comprehensive review of ultrasound-based surface acoustic wave elastography techniques, including their theoretical foundations, technical implementations, and existing medical applications. The goal is to provide a concise summary of the state-of-the-art of this field, hoping to offer a reliable reference for the further development of these techniques and foster the expansion of their medical applications.

Upper extremity soft tissue stiffness measured with shear wave elastography: A between-day reliability study

Background

Imbalances in soft tissue stiffness (STS) of the pectoralis and common wrist extensors (CWEs) can adversely alter upper extremity function. Shear wave elastography (SWE) has the capacity to provide precise, repeatable, objective data on STS. The purpose of this study was to determine the between-day intrarater reliability for the pectoralis and CWE tendon stiffness as measured by SWE.

Methods

STS measured by the shear wave modulus (kilopascals (kPa)) was captured bilaterally on the pectoralis major, pectoralis minor, and CWE tendon using 2D SWE ultrasound imaging (GE Logiq S8, 9 L transducer) on two separate days. Within examiner intraclass correlation coefficients (ICC (3, 3)) with 95% confidence intervals, standard error of the measure, and minimal detectable changes were calculated.

Results

The investigators recruited 10 healthy participants (mean age = 23.50  ±  1.43). Between day intrarater reliability values were obtained for the dominant pectoralis major ICC  =  0.70 (-0.15, -0.93), nondominant pectoralis major ICC  =  0.63 (-0.30, -0.91), dominant pectoralis minor ICC  = 0 .72(-0.04, -0.93), nondominant pectoralis minor ICC  = 0.75(0.08, -0.94), dominant CWE tendon ICC  =  0.75(-0.08, -0.94), and nondominant CWE tendon ICC  =  0.75(-0.12, -0.94).

Discussion

Our data demonstrate acceptable reliability but future studies should include methods that control for variables known to effect STS.

The longitudinal study of muscle changes with ultrasound: differential changes in idiopathic inflammatory myopathy subgroups

OBJECTIVES

We investigated shear wave elastography (SWE), B mode US and power Doppler (PDUS) as imaging biomarkers for longitudinal follow-up in idiopathic inflammatory myopathy (IIM), with a particular focus on immune-mediated necrotizing myopathy (IMNM) and DM.

METHODS

Participants had serial SWE, PDUS on the deltoid (D) and vastus lateralis (VL) muscles on four occasions at intervals of 3-6 months. Clinical assessments included manual muscle testing, and patient- and physician-reported outcome scales.

RESULTS

Thirty-three participants were included: IMNM = 17, DM = 12, overlap myositis = 3, PM = 1. Twenty were in a prevalent clinic group, and 13 were recently treated cases in an incident group. Differential changes in SWS and US domains occurred with time in both the prevalent and incident groups. In the VL-prevalent subgroup, echogenicity increased over time (P = 0.040), while in the incident cases there was a trend for reduction to normal over time (P = 0.097) with treatment. Muscle bulk reduced in the D-prevalent subgroup over time (P = 0.096), suggesting atrophy. SWS also reduced in the VL-incident subgroup over time (P = 0.096), suggesting a trend towards improvement in muscle stiffness with treatment.

CONCLUSION

SWE and US appear promising as imaging biomarkers for patient follow-up in IIM and indicate changes over time, especially with echogenicity, muscle bulk and SWS in the VL. Due to the limitations of the participant numbers, additional studies with a larger cohort are needed to help evaluate these US domains further and outline specific characteristics within the IIM subgroups.

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.

Analysis of the thenar muscles with ultrasound shear wave elastography: Reliability and preliminary findings

INTRODUCTION/AIMS

Ultrasound shear wave elastography (SWE) of the thenar muscles has the potential to provide a simple and noninvasive assessment of the severity of carpal tunnel syndrome (CTS), but its reliability is unknown. The purpose of this study was to assess the intra- and inter-rater reliability of SWE measurements of the elastic modulus of individual thenar muscles, to assess their suitability for clinical application.

METHODS

Fourteen healthy volunteers, seven male and seven female, participated in this study. The elastic modulus of the thenar muscles was measured with SWE, with two independent examiners to assess inter-rater reliability. The first examiner also performed a second measurement after an interval of least 1 day to assess intra-rater reliability. Reliability was evaluated using an intraclass correlation coefficient (ICC) and 95% confidence interval (CI).

RESULTS

For the abductor pollicis brevis (APB) and opponens pollicis (OPP), the CI of ICC in intra-rater reliability was 0.47-0.85 and 0.56-0.88, respectively. The CI of ICC in inter-rater reliability was 0.27-0.78 for the APB and 0.22-0.76 for the OPP. The ICCs of intra- and/or inter-rater reliability of other thenar muscles were less than 0.5.

DISCUSSION

In this study, SWE evaluations of thenar muscles were quite variable in terms of their reliability. A larger study will be needed to determine the source of this variability, improve reliability, and assess the value of SWE in the evaluation of the severity of CTS.

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.

Skeletal Muscle Assessment Using Quantitative Ultrasound: A Narrative Review

Ultrasound (US) is an important imaging tool for skeletal muscle analysis. The advantages of US include point-of-care access, real-time imaging, cost-effectiveness, and absence of ionizing radiation. However, US can be highly dependent on the operator and/or US system, and a portion of the potentially useful information carried by raw sonographic data is discarded in image formation for routine qualitative US. Quantitative ultrasound (QUS) methods provide analysis of the raw or post-processed data, revealing additional information about normal tissue structure and disease status. There are four QUS categories that can be used on muscle and are important to review. First, quantitative data derived from B-mode images can help determine the macrostructural anatomy and microstructural morphology of muscle tissues. Second, US elastography can provide information about muscle elasticity or stiffness through strain elastography or shear wave elastography (SWE). Strain elastography measures the induced tissue strain caused either by internal or external compression by tracking tissue displacement with detectable speckle in B-mode images of the examined tissue. SWE measures the speed of induced shear waves traveling through the tissue to estimate the tissue elasticity. These shear waves may be produced using external mechanical vibrations or internal "push pulse" ultrasound stimuli. Third, raw radiofrequency signal analyses provide estimates of fundamental tissue parameters, such as the speed of sound, attenuation coefficient, and backscatter coefficient, which correspond to information about muscle tissue microstructure and composition. Lastly, envelope statistical analyses apply various probability distributions to estimate the number density of scatterers and quantify coherent to incoherent signals, thus providing information about microstructural properties of muscle tissue. This review will examine these QUS techniques, published results on QUS evaluation of skeletal muscles, and the strengths and limitations of QUS in skeletal muscle analysis.

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.

Reproducibility and feasibility of a handheld ultrasound device compared to a standard ultrasound machine in muscle thickness measurements

Objective

To test the feasibility and reproducibility of a handheld ultrasound device (HUD) compared to a standard ultrasound machine for muscle thickness measurements in healthy participants.

Methods

A prospective cross-sectional study was designed where two novice operators tested the thickness of the vastus lateralis, rectus femoris, and vastus intermedius muscles on recruited asymptomatic participants with no history of muscle diseases. The anterior-posterior thickness of each muscle was measured three times per operator to evaluate intra-operator reproducibility and using two machines to evaluate inter-system reproducibility. Scanning started using the HUD followed by the standard system. Intraclass correlation coefficients (ICC) and simple linear regression were used to test for reproducibility and proportional bias respectively.

Results

A total of 33 male participants volunteered to take part in this study with a mean age of 22.7 years (6.8). Intra-operator reproducibility was almost perfect for both operators on both machines (ICC > 0.80). The measurements difference percentage between the machines ranged from 1.8% to 6.6% and inter-system reproducibility ICC ranged from 0.815 to 0.927 showing excellent reproducibility. Inter-operator reproducibility was poor to moderate on both machines (ICC: 0.522-0.849). Regression analysis showed no proportional bias in the measurements. All measurements were completed successfully using the HUD.

Conclusion

The HUD demonstrated excellent accuracy compared to the standard ultrasound machine for measuring thigh muscle thickness.

Passive muscle stiffness is correlated with the intramuscular adipose tissue in young individuals

PURPOSE

We investigated the relationship between intramuscular adipose tissue (IntraMAT) and muscle stiffness (passive and mechanical) and lengthening in young individuals, hypothesizing that (1) passive muscle stiffness is negatively correlated with the IntraMAT content, and (2) the IntraMAT content is negatively correlated with mechanical changes in muscle stiffness and fascicle length during passive dorsiflexion.

METHODS

Twenty men and women (20.3 ± 1.3 years) participated in this study. Axial T1-weighted magnetic resonance imaging was performed at the thickest point of the medial gastrocnemius (MG) to measure the IntraMAT cross-sectional area (CSA) and muscle tissue CSA (units; cm²). The shear wave velocity (SWV) and fascicle length at the three ankle joint angles, namely 15° with plantarflexion (PF15), 0° with neutral position (NP), and 15° with dorsiflexion (DF15), were measured as parameters of muscle stiffness (unit; m/s) and lengthening (unit; cm) using ultrasound shear wave elastography and B-mode imaging. We further calculated the changes in SWV and fascicle length from PF15 to NP and from NP to DF15 as mechanical muscle stiffness and lengthening, respectively.

RESULTS

There was a relationship between IntraMAT CSA and absolute SWV at DF15 (r = - 0.47, P < 0.05). Further, a relationship was observed between IntraMAT CSA and change in SWV and fascicle length from NP to DF15 (r = - 0.47 and r = 0.59, P < 0.05); whereas no relationship was observed between changes in fascicle length and muscle SWV (r = - 0.23, P = 0.33).

CONCLUSION

These results may indicate biomechanical and/or physiological associations between IntraMAT CSA and passive muscle stiffness.

Evaluation of Accuracy of Shear Wave Elastography and Superb Microvascular Imaging Methods in Diagnosis of Piriformis Syndrome: A Preliminary Study

Piriformis syndrome is a neuromuscular disease resulting from sciatic nerve compression caused by an abnormal condition in the piriformis muscle. Superb microvascular imaging (SMI) is a new ultrasound imaging technique that visualizes low-velocity and small-diameter blood vessel flow. In our prospectively designed study, we aimed to evaluate the accuracy of diagnosis of piriformis syndrome with innovative methods such as shear wave elastography (SWE) and SMI. Thirty-two patients diagnosed with unilateral piriformis syndrome were accepted to the statistical stage. The side without symptoms was considered the "unaffected side." Bilateral piriformis muscles were examined by ultrasonography. Muscle thickness was determined on gray scale, stiffness on SWE and vascularity characteristics on power Doppler and SMI by two independent radiologists. Piriformis muscle stiffness on the non-pathological (unaffected) side was measured by SWE as 18.27 ± 7.301 kPa, and the mean stiffness on the pathological side was 29.70 ± 10.095 kPa. Pathological side muscle stiffness was significantly higher (p < 0.05). Using innovative methods such as SWE and SMI in addition to conventional ultrasonography as much as possible in our daily practice and research helps us in making the correct diagnosis in piriformis syndrome.

Using Shear-Wave Elastography to Assess Exercise-Induced Muscle Damage: A Review

Shear-wave elastography is a method that is increasingly used to assess muscle stiffness in clinical practice and human health research. Recently, shear-wave elastography has been suggested and used to assess exercise-induced muscle damage. This review aimed to summarize the current knowledge of the utility of shear-wave elastography for assessment of muscle damage. In general, the literature supports the shear-wave elastography as a promising method for assessment of muscle damage. Increases in shear modulus are reported immediately and up to several days after eccentric exercise, while studies using shear-wave elastography during and after endurance events are showing mixed results. Moreover, it seems that shear modulus increases are related to the decline in voluntary strength loss. We recommend that shear modulus is measured at multiple muscles within a muscle group and preferably at longer muscle lengths. While further studies are needed to confirm this, the disruption of calcium homeostasis seems to be the primary candidate for the underlying mechanism explaining the increases in shear modulus observed after eccentric exercise. It remains to be investigated how well the changes in shear modulus correlate with directly assessed amount of muscle damage (biopsy).

Anisotropy in ultrasound shear wave elastography: An add-on to muscles characterization

Ultrasound shear wave elastography was developed the past decade, bringing new stiffness biomarker in clinical practice. This biomarker reveals to be of primarily importance for the diagnosis of breast cancer or liver fibrosis. In muscle this biomarker become much more complex due to the nature of the muscle itself: an anisotropic medium. In this manuscript we depict the underlying theory of propagating waves in such anisotropic medium. Then we present the available methods that can consider and quantify this parameter. Advantages and drawbacks are discussed to open the way to imagine new methods that can free this biomarker in a daily clinical practice.

Acute effect of resistance exercise at different velocities on stiffness and vascularity of the biceps brachii muscle: a preliminary study

Background

Resistance exercise can be defined as the percentage of maximal strength (%1 repetition maximum) used for a particular exercise. Shear wave elastography (SWE) is a robust and novelty imaging technique that provides information regarding tissue stiffness. Superb microvascular imaging (SMI) is a non-irradiating technique that can provide quantitative measurement of muscle blood flow non-invasively.

Purpose

To compare the acute effects of low- and high-velocity resistance exercise on stiffness and blood flow in the biceps brachii muscle (BBM) using SWE and SMI.

Material and Methods

This prospective study included 60 healthy men (mean age=28.9 years; age range=26–34 years). BBM stiffness was measured by using SWE at rest, after low- and high-velocity resistance exercise, and muscle blood flow was also evaluated by SMI. Resistance exercise was performed using a dumbbell with a mass adjusted to 70%–80% of one-repetition maximum.

Results

The stiffness values increased significantly from resting to high- and low-velocity resistance exercises. There was no significant difference between the elastography values of the BBM after the high- and low-velocity resistance exercise. The blood flow increased significantly from resting to high- and low-velocity resistance exercises. Blood flow increase after low-velocity exercise was significantly higher compared to high-velocity exercise.

Conclusion

While muscle stiffness parameters and blood flow significantly increased from resting after both high- and low-velocity resistance exercises, blood flow significantly increased after low-velocity exercise compared to high-velocity exercise. This can mean that metabolic stress, an important trigger for muscle development, is more likely to occur in low-velocity exercise.

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°).

A scoping review of methods used in musculoskeletal soft tissue and nerve shear wave elastography studies

This scoping review of shear wave elastography (SWE) articles in musculoskeletal soft tissue and nerve research demonstrates methodological heterogeneity resulting from a lack of standardized data collection and reporting requirements. Seven literature databases were searched for original articles published in English from 2004-2020 that examine human skeletal muscles, tendons, and nerves in vivo. Although 5,868 records were initially identified, only 375 reports met inclusion criteria. Of the 375 articles, 260 examined 89 unique muscles, 94 examined 14 unique tendons, and 43 examined 8 unique nerves. Cohorts were often small (n = 11-20) and young (mean = 20-29 years), and participants were typically tested in the prone position. Regarding equipment, a variety of ultrasound systems (n = 11), ultrasound models (n = 18), and transducers (n = 19) were identified. Only 11% of articles contained information on the use of electromyography to confirm absence of muscle activity, and only 8% reported measurement depth. Since musculoskeletal soft tissue and nerve stiffness can vary significantly based on data collection methods, it is essential to standardize SWE collection and reporting procedures. This will allow SWE to serve as a valid and reproducible tool for assessing tissue pathology, disease progression, and response to intervention within a variety of musculoskeletal and nerve-related disorders.

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.

Limitations of Muscle Ultrasound Shear Wave Elastography for Clinical Routine-Positioning and Muscle Selection

Shear wave elastography (SWE) is a clinical ultrasound imaging modality that enables non-invasive estimation of tissue elasticity. However, various methodological factors—such as vendor-specific implementations of SWE, mechanical anisotropy of tissue, varying anatomical position of muscle and changes in elasticity due to passive muscle stretch—can confound muscle SWE measurements and increase their variability. A measurement protocol with a low variability of reference measurements in healthy subjects is desirable to facilitate diagnostic conclusions on an individual-patient level. Here, we present data from 52 healthy volunteers in the areas of: (1) Characterizing different limb and truncal muscles in terms of inter-subject variability of SWE measurements. Superficial muscles with little pennation, such as biceps brachii, exhibit the lowest variability whereas paravertebral muscles show the highest. (2) Comparing two protocols with different limb positioning in a trade-off between examination convenience and SWE measurement variability. Repositioning to achieve low passive extension of each muscle results in the lowest SWE variability. (3) Providing SWE shear wave velocity (SWV) reference values for a specific ultrasound machine/transducer setup (Canon Aplio i800, 18 MHz probe) for a number of muscles and two positioning protocols. We argue that methodological issues limit the current clinical applicability of muscle SWE.

Utility of shear wave elastography and high-definition color for diagnosing carpal tunnel syndrome

OBJECTIVE

The diagnostic values of measuring median nerve (MN) stiffness and vascularity with shear wave elastography (SWE) and high-definition (HD) color were investigated in carpal tunnel syndrome (CTS).

METHODS

Seventy patients (123 wrists) with CTS and thirty-five healthy volunteers (70 wrists) were enrolled. Based on nerve conduction studies (NCS), the patients were subdivided into NCS-negative, mild-to-moderate, and severe CTS groups. MN and abductor pollicis brevis (APB) SWE and MN HD color were performed on a longitudinal plane.

RESULTS

The mild-to-moderate and severe CTS groups showed increased MN stiffness at the wrist and MN stiffness ratio (wrist-to forearm) compared with the control (p < 0.001). The NCS-negative CTS group showed increased MN stiffness at the wrist (p = 0.022) and MN stiffness ratio (p = 0.032) compared with the control. The severe CTS group showed increased MN stiffness at the wrist compared with the mild-to-moderate CTS group (p = 0.034). The cutoff-values in diagnosing NCS-confirmed CTS were 50.12 kPa for MN stiffness at the wrist, 1.91 for MN stiffness ratio, and grade 1 for HD color.

CONCLUSIONS

SWE and HD color are good supportive tools in diagnosing and assessing severity in CTS.

SIGNIFICANCE

SWE and HD color demonstrated that MN in CTS was associated with increased stiffness and hypervascularity.

Effect of Resonant Frequency Vibration on Delayed Onset Muscle Soreness and Resulting Stiffness as Measured by Shear-Wave Elastography

This study utilized resonant frequency vibration to the upper body to determine changes in pain, stiffness and isometric strength of the biceps brachii after eccentric damage. Thirty-one participants without recent resistance training were randomized into three groups: a Control (C) group and two eccentric exercise groups (No vibration (NV) and Vibration (V)). After muscle damage, participants in the V group received upper body vibration (UBV) therapy for 5 min on days 1-4. All participants completed a visual analog scale (VAS), maximum voluntary isometric contraction (MVIC), and shear wave elastography (SWE) of the bicep at baseline (pre-exercise), 24 h, 48 h, and 1-week post exercise. There was a significant difference between V and NV at 24 h for VAS (p = 0.0051), at 24 h and 1-week for MVIC (p = 0.0017 and p = 0.0016, respectively). There was a significant decrease in SWE for the V group from 24-48 h (p = 0.0003), while there was no significant change in the NV group (p = 0.9341). The use of UBV resonant vibration decreased MVIC decrement and reduced VAS pain ratings at 24 h post eccentric damage. SWE was strongly negatively correlated with MVIC and may function as a predictor of intrinsic muscle state in the time course of recovery of the biceps brachii.

Quantitative assessment of change in upper extremity muscle stiffness following fluid injection using shear wave elastography

OBJECTIVE

To quantitatively assess changes in muscle stiffness following intramuscular saline injection using shear wave elastography (SWE).

MATERIALS AND METHODS

Thirty muscles (lateral deltoid (LD), biceps brachii (BB), brachialis, pronator teres (PT), flexor carpi radialis (FCR), flexor carpi ulnaris (FCU)) from fresh-frozen cadaveric specimens were injected with saline under ultrasound guidance. Pre- and post-injection muscle thickness (MT) (mm) and SWE (kPa) measurements were recorded.

RESULTS

All muscles demonstrated a decrease in the mean SWE value post-injection, with the largest differences ± standard error noted in the LD (14.76 ± 3.55 kPa, p = 0.021) and brachialis muscles (12.02 ± 2.51 kPa, p = 0.013). Muscle thickness increased following injection, although the degree of changes poorly correlated with the change in SWE.

CONCLUSION

In summary, following intramuscular injection of saline injection, a decrease in upper extremity muscle stiffness is detected using SWE. It is important to note that if performing a longitudinal assessment of muscle stiffness after intramuscular injection, saline will likely contribute to a decrease in muscle stiffness in the immediate post-injection time period.

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.

Muscle shear wave elastography, conventional B mode and power doppler ultrasonography in healthy adults and patients with autoimmune inflammatory myopathies: a pilot cross-sectional study

Background

Before the role of shear wave elastography (SWE) and B mode ultrasound (US) in the diagnosis of different forms of idiopathic inflammatory myopathies (IIM) can be investigated, normative data is required. This study aimed to describe and then compare normative SWE and B mode ultrasound metrics of muscles in healthy controls and patients with IIM.

Methods

Twenty nine healthy adult controls and 10 IIM patients (5 with inclusion body myositis and 5 with necrotising autoimmune myopathy) underwent a full clinical examination, laboratory investigations, SWE and US measurements of selected proximal and distal limb muscles. Shear wave speed (SWS) and multiple US domains [echogenicity, fascial thickness, muscle bulk and power Doppler (PD)] were measured in both groups.

Results

In healthy controls (n = 29; mean age 46.60 ± 16.10; 44.8 % female), age was inversely correlated with SWS at the deltoid (stretch) (Rs. -0.40, p = 0.030) and PD score at the deltoid (rest) (Rs. -0.40, P = 0.032). Those ≥ 50 years old had a lower SWS at the deltoid (stretch) compared to the < 50 year group (2.92 m/s vs. 2.40 m/s, P = 0.032). Age correlated with increased echogenicity in the flexor digitorum profundus (Rs. 0.38, P = 0.045). Females had a smaller muscle bulk in the deltoid (P = 0.022). Body mass index (BMI) was inversely associated with SWS in the deltoid (stretch) (Rs – 0.45, P = 0.026), and positively correlated with echogenicity in the deltoid (Rs. 0.69, P = 0.026). In patients ≥50 years of age, patients with IIM (mean age 61.00 ± 8.18; females 20.0 %) had a higher proportion of abnormal echogenicity scores at the flexor digitorum profundus (FDP) (40.00 % vs. 14.30 %, P = 0.022) and tibialis anterior (TA) (80.00 % vs. 28.60 %, P = 0.004). Fascial thickness was lower in the FDP (0.63mm vs. 0.50mm, p = 0.012) and TA (0.58mm vs. 0.45mm, P = 0.001).

Conclusions

Our findings suggest there is scope for US techniques to be useful for diagnostic screening of affected muscles in patients with IIM, especially in those with suspected inclusion body myositis or necrotising autoimmune myopathy. We provide normative data for future studies into SWE and US techniques in skeletal muscle. The differences between IIM patients and controls warrant further study in a broader IIM patient cohort.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04424-0.

Elastographic Region of Interest Determination for Muscle with Fat Infiltration

Purpose

Ultrasound elastography has been used to evaluate the skeletal muscle stiffness as a biomarker for sarcopenia assessment. However, there is no consensus with respect to the size and location of the region of interest in assessing such fat infiltrated muscle. The objective of this study was to determine which cross-sectional area should be measured in torn disuse muscle with fat infiltration to accurately measure muscle activity using real-time tissue elastography (RTE).

Methods

Twenty-seven patients, whose rotator cuff muscle with torn tendon was successfully repaired, were followed by programmed rehabilitation. RTE measurements of the supraspinatus muscle were obtained during muscle contraction before and one-year after surgery so that the activity value was defined as the difference between elastography measurements at rest and elastography measurements during contraction. Given that the patients with successfully repaired and completed rehabilitation showed an increased activity value, the sensitivity for three regions of interest; posterior portion of the anterior-middle subregion (AM-p), anterior region (AR), and whole cross-sectional area of the supraspinatus (whole) were compared with the number of patients showing an increase in activity values as sensitivity analysis.

Results

The sensitivity showing an increase in activity values was 74.1% for the AM-p area, 70.4% for the AR area, and 81.5% for the whole area. Intraclass correlation coefficient_1,3 was 0.87–0.97 for the AM-p area, 0.88–0.98 for the AR area and 0.92–0.99 for the whole area.

Conclusion

The whole cross-sectional area is suitable to measure muscle activity in muscle with fat infiltration. The results in this study will provide some beneficial information when ultrasound elastography is used for the assessment of sarcopenia muscle with fat infiltration.

Relationship between shear elastic modulus and passive force of the human rectus femoris at multiple sites: a Thiel soft-embalmed cadaver study

PURPOSE

Estimation of muscle passive force from elasticity using shear wave elastography (SWE) has been reported. However, the relationship between the elasticity and passive force of human muscles has not been elucidated. This study investigated the elastic modulus-passive force relationship in human skeletal muscles at multiple sites.

METHODS

Four rectus femoris (RF) muscles were dissected from a human Thiel-embalmed cadaver. Calibration weights (0-600 g in 60-g increments) were applied to the distal tendon via a pulley system, and the shear elastic modulus as an index of elasticity was measured using SWE. The shear elastic modulus of the RF was measured at the proximal, central, and distal portions.

RESULTS

The results demonstrated that the relationships between the elasticity in the longitudinal direction of the muscle and the passive force were nearly linear for all tested sites, with coefficients of determination ranging from 0.813 to 0.993.

CONCLUSION

Shear wave elastography may be used as an indirect method to measure the changing passive force at any site within human muscles.

Muscle Ultrasound Shear Wave Elastography as a Non-Invasive Biomarker in Myotonia

Myotonia, i.e., delayed muscle relaxation in certain hereditary muscle disorders, can be assessed quantitatively using different techniques ranging from force measurements to electrodiagnostics. Ultrasound shear wave elastography (SWE) has been proposed as a novel tool in biomechanics and neuromuscular medicine for the non-invasive estimation of muscle elasticity and, indirectly, muscle force. The aim of this study is to provide ‘proof-of-principle’ that SWE allows a quantitative measurement of the duration of delayed muscle relaxation in myotonia in a simple clinical setting. In six myotonic muscle disorder patients and six healthy volunteers, shear wave velocities (SWV) parallel to the fiber orientation in the flexor digitorum superficialis muscle in the forearm were recorded with a temporal resolution of one per second during fist-clenching and subsequent relaxation; the relaxation time to 10% of normalized shear wave velocity (RT_0.1) was calculated. Forty-six SWE imaging sequences were acquired, yielding a mean RT_0.1 of 7.38 s in myotonic muscle disorder patients, significantly higher than in healthy volunteers (1.36 s), which is comparable to data obtained by mechanical dynamometry. SWV measurements during the baseline relaxation and voluntary contraction phases did not differ significantly between groups. We conclude that SWE is a promising, non-invasive, widely available tool for the quantitative assessment of myotonia to aid in diagnosis and therapeutic monitoring.

Reliability and Validity of Ultrasound Elastography for Evaluating Muscle Stiffness in Neurological Populations: A Systematic Review and Meta-Analysis

OBJECTIVE

Ultrasound elastography is an emerging diagnostic technology used to investigate the biomechanical properties of the musculoskeletal system. The purpose of this study was to systematically review the psychometric properties of ultrasound elastography techniques for evaluating muscle stiffness in people with neurological conditions.

METHODS

A systematic search of MEDLINE, EMBASE, CINAHL, and Cochrane Library databases was performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Using software, reviewers independently screened citations for inclusion. Peer-reviewed studies that evaluated in vivo muscle stiffness in people with neurological conditions and reported relevant psychometric properties were considered for inclusion. Twenty-one articles were included for final review. Data relevant to measurement technique, site, and neurological condition were extracted. The Consensus-Based Standards for the Selection of Health Measurement Instruments checklist was used to rate the methodological quality of included studies. The level of evidence for specific measurement outcomes was determined using a best-evidence synthesis approach.

RESULTS

Reliability varied across populations, ultrasound systems, and assessment conditions (ie, joint/body positions, active/passive muscle conditions, probe orientation), with most studies indicating moderate to good reliability (ICC = 0.5-0.9, n = 13). Meta-analysis results showed a good overall correlation across studies (r = 0.78, 95% confidence interval = 0.64-0.86), with no between-group difference based on population (Q1 = 0.00). Convergent validity was demonstrated by strong correlations between stiffness values and measures of spasticity (n = 5), functional motor recovery or impairment (n = 5), and grayscale or color histogram pixel intensities (n = 3). Discriminant or known-groups validity was also established for multiple studies and indicated either significant between-group differences in stiffness values (n = 12) or within-group differences between more and less affected limbs (n = 6). Responsiveness was observed in all intervention studies reporting posttreatment stiffness changes (n = 6).

CONCLUSIONS

Overall, ultrasound elastography techniques showed moderate reliability in evaluating in vivo muscle stiffness, good convergent validity with relevant clinical assessments, and good divergent validity in discriminating tissue changes within and between groups.

IMPACT

Ultrasound elastography has clinical utility in assessing muscle stiffness, monitoring its temporal changes, and measuring the response to intervention in people with neurological conditions.

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.

Eccentric Exercise Reduces Upper Trapezius Muscle Stiffness Assessed by Shear Wave Elastography and Myotonometry

In this study, we tested the hypotheses that unaccustomed eccentric exercise (ECC) would reduce the elastic modulus and dynamic stiffness of the upper trapezius muscle and that these changes would correlate with increases in muscle thickness, reflecting muscle edema. Shear wave elastography was used to measure elastic modulus, dynamic stiffness was assessed using myotonometry, and muscle thickness was measured using ultrasonography. All measurements were performed at four locations over the upper trapezius before and 24 h after a single bout of ECC. Fourteen healthy participants (11 males and 3 females; 23.2 ± 3.0 years; height 175.1 ± 10.4 cm; body mass 73.8 ± 11.3 kg) took part in the study. Overall, ECC resulted in decreased elastic modulus (from 45.8 ± 1.6 to 39.4 ± 1.2 kPa, p < 0.01) and dynamic muscle stiffness (from 369.0 ± 7.3 to 302.6 ± 6.0 N/m, p < 0.01). Additionally, ECC resulted in increased muscle thickness (from 6.9 ± 0.4 to 7.3 ± 0.4 mm, p < 0.01). Spatial changes (across the four locations) were found for elastic modulus, stiffness and thickness. No significant correlations were found between changes in measures of muscle stiffness, or between changes in stiffness and changes in thickness. In conclusion, the present pilot study showed that ECC altered biomechanical muscle properties, reflected by decreased elastic modulus and dynamic muscle stiffness 24 h after ECC.

Novel Muscle Imaging in Inflammatory Rheumatic Diseases-A Focus on Ultrasound Shear Wave Elastography and Quantitative MRI

In recent years, imaging has played an increasing role in the clinical management of patients with rheumatic diseases with respect to aiding diagnosis, guiding therapy and monitoring disease progression. These roles have been underpinned by research which has enhanced our understanding of disease pathogenesis and pathophysiology of rheumatology conditions, in addition to their key role in outcome measurement in clinical trials. However, compared to joints, imaging research of muscles is less established, despite the fact that muscle symptoms are very common and debilitating in many rheumatic diseases. Recently, it has been shown that even though patients with rheumatoid arthritis may achieve clinical remission, defined by asymptomatic joints, many remain affected by lingering constitutional systemic symptoms like fatigue, tiredness, weakness and myalgia, which may be attributed to changes in the muscles. Recent improvements in imaging technology, coupled with an increasing clinical interest, has started to ignite new interest in the area. This perspective discusses the rationale for using imaging, particularly ultrasound and MRI, for investigating muscle pathology involved in common inflammatory rheumatic diseases. The muscles associated with rheumatic diseases can be affected in many ways, including myositis-an inflammatory muscle condition, and myopathy secondary to medications, such as glucocorticoids. In addition to non-invasive visual assessment of muscles in these conditions, novel imaging techniques like shear wave elastography and quantitative MRI can provide further useful information regarding the physiological and biomechanical status of the muscle.

Reproducibility of shear wave elastography among operators, machines, and probes in an elasticity phantom

PURPOSE

This study was aimed to investigate the reproducibility of shear wave elastography (SWE) among operators, machines, and probes in a phantom, and to evaluate the effect of depth of the embedded inclusions and the accuracy of the measurements.

METHODS

In vitro stiffness measurements were made of six inclusions (10, 40, and 60 kPa) embedded at two depths (1.5 cm and 5 cm) in an elastography phantom. Measurements were obtained by two sonographers using two ultrasound machines (the SuperSonic Imagine Aixplorer with the XC6-1, SL10-2 and SL18-5 probes, and the General Electric LOGIQ E9 with the 9L-D probe). Variability was evaluated using the coefficient of variation. Reproducibility was calculated using intraclass correlation coefficients (ICCs).

RESULTS

For shallow inclusions, low variability was observed between operators (range, 0.9% to 5.4%). However, the variability increased significantly for deep inclusions (range, 2.4% to 80.8%). The measurement difference between the operators was 1%-15% for superficial inclusions and 3%-43% for deep inclusions. Inter-operator reproducibility was almost perfect (ICC>0.90). The measurement difference between machines was 0%-15% for superficial inclusions and 38.6%-82.9% for deep inclusions. For superficial inclusions, the reproducibility among the three probes was excellent (ICC>0.97). The mean stiffness values of the 10 kPa inclusion were overestimated by 16%, while those of the 40 kPa and 60 kPa inclusions were underestimated by 42% and 48%, respectively.

CONCLUSION

Phantom SWE measurements were only reproducible among operators, machines, and probes at superficial depths. SWE measurements acquired in deep regions should not be used interchangeably among operators, machines, or probes.

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.

Inter- and intra-reader reproducibility of shear wave elastography measurements for musculoskeletal soft tissue masses

OBJECTIVE

To determine inter- and intra-reader reproducibility of shear wave elastography measurements for musculoskeletal soft tissue masses.

MATERIALS AND METHODS

In all, 64 patients with musculoskeletal soft tissue masses were scanned by two readers prior to biopsy; each taking five measurements of shear wave velocity (m/s) and stiffness (kPa). A single lesion per patient was scanned in transverse and cranio-caudal planes. Depth measurements (cm) and volume (cm³) were recorded for each lesion, for each reader. Linear mixed modelling was performed to assess limits of agreement (LOA), inter- and intra-reader repeatability, including analyses for measured depth and volume.

RESULTS

Of the 64 lesions scanned, 24 (38%) were malignant. Bland-Altman plots demonstrated negligible bias with wide LOA for all measurements. Transverse velocity was the most reliable measure-intraclass correlation (95% CI) = 0.917 (0.886, 1)-though reader 1 measures could be between 38% lower and 57% higher than reader 2 [ratio-scale bias (95% LOA) = 0.99 (0.64, 1.55)]. Repeatability coefficients indicated most disagreement resulted from poor within-reader reproducibility. LOA between readers calculated from means of five repeated measurements were narrower-transverse velocity ratio-scale bias (95% LOA) = 1.00 (0.74, 1.35). Depth affected both estimated velocity and repeatability; volume also affected repeatability.

CONCLUSION

This study found poor repeatability of measurements with wide LOA due mostly to intra-reader variability. Transverse velocity was the most reliable measure; variability may be affected by lesion depth. At least five measurements should be reported with LOA to assist future comparability between shear wave elastography systems in evaluating soft tissue masses.

Assessment of the Passive Tension of the First Dorsal Interosseous and First Lumbrical Muscles Using Shear Wave Elastography

PURPOSE

Quantitative evaluation of passive tension of the intrinsic muscles of the hand is necessary to assess contracture of the intrinsic muscles accurately. The aim of this study was to evaluate the shear modulus, which is related to passive muscle tension, of the first dorsal interosseous (FDI) and first lumbrical (FL) muscles using shear wave elastography.

METHODS

Subjects were 18 healthy males. The shear modulus of the FDI and FL muscles was assessed at several proximal interphalangeal (PIP), distal interphalangeal (DIP), metacarpophalangeal (MCP), and wrist joint positions. The position in which the MCP joint was flexed 60° past 0° with PIP-DIP joint extension and that in which the MCP joint was extended 30° past 0° with PIP-DIP joint flexion were respectively defined as the slack and stretched positions. We analyzed whether the shear modulus was affected by finger position (slack or stretched), wrist position (30° flexion past 0° and 30° extension past 0°), and muscle (FDI or FL).

RESULTS

Shear modulus in the stretched position was significantly higher than that in the slack position. The shear modulus of the FL muscle at 30° wrist extension was significantly higher than that at 30° flexion. The shear modulus of the FL muscle was significantly higher than that of the FDI muscle in the stretched position with the wrist at 30° flexion and extension, and in the slack position with the wrist at 30° extension.

CONCLUSIONS

The shear modulus of the FDI and FL muscles increased with MCP joint extension and PIP-DIP joint flexion. The difference in the muscle characteristics between the FDI and FL muscles should be considered when evaluating or treating contractures of the intrinsic muscles.

CLINICAL RELEVANCE

Shear wave elastography can evaluate the condition of the intrinsic muscles of the hand quantitatively.

The effect of ageing on shear wave elastography muscle stiffness in adults

Background

Skeletal muscle undergoes structural changes with ageing which may alter its biomechanical properties. Shear wave elastography (SWE) may detect these changes by measuring muscle stiffness.

Aims

To investigate muscle stiffness in healthy young, middle-aged and elderly cohorts using SWE and correlate it with muscle strength and mass.

Methods

Shear wave velocity (SWV) was measured in the quadriceps, hamstrings and biceps brachii of 26 young (range 20–35 years), 21 middle-aged (40–55) and 30 elderly (77–94) volunteers. The participants performed several muscle tests to evaluate their strength. The One-way ANOVA was used to test the muscle stiffness differences between the groups and the Pearson’s correlation coefficient to evaluate the relationship between SWV and muscle strength.

Results

The overall resting muscle SWV gradually decreased with age but was only significantly reduced in the elderly group (p < 0.001); with the exception of the vastus lateralis SWV where a significant difference was noted (p < 0.05) between young (1.77 m/s), middle-aged (1.64 m/s) and elderly (1.48 m/s). The elderly group had on average 16.5% lower muscle stiffness compared to the young. SWV significantly correlated with muscle mass (r = 0.316), walking time (r = − 0.560), number of chair stands (r = 0.522), handgrip strength (r = 0.436) and isokinetic knee strength (r = 0.640). Sex and BMI did not explain any significant variation in SWV.

Conclusions

Ageing was associated with a decline in skeletal muscle stiffness which positively correlates with muscle weakness. Further research is needed to evaluate the promising role of SWE as a biomarker for sarcopenia assessment and potential falls risk prediction in elderly individuals.

Electronic supplementary material

The online version of this article (10.1007/s40520-019-01139-0) contains supplementary material, which is available to authorized users.

Measurement of the shear modulus in thin-layered tissues using numerical simulations and shear wave elastography

Measurement of mechanical properties of thin-layered tissues has broad applications in the diagnosis of several pathologies. Ultrasound shear wave elastography (SWE) measures the shear wave speed as a means of estimating the mechanical properties of tissues. However, the wave speed in thin-layered tissues is affected by their thickness and the properties of surrounding tissues. The objective of this study is to introduce a method that combines numerical simulations and SWE measurements to provide a more accurate calculation of shear modulus in layered tissues. In the proposed method, the spatial distribution of the acoustic radiation force (ARF) emitted by the transducer was first computed. The ARF was then used as input for simulating the guided wave propagation in the thin layer with its surroundings. The simulations were repeated for several values of the shear modulus of the layer to obtain the corresponding simulated wave speed. By comparing the measured and simulated wave speeds, a more accurate (corrected) shear modulus can be obtained. The proposed method was validated using experiments in agarose gels. In-vivo SWE measurements were also performed for the fascia of the tibialis anterior (TA) muscle and the aponeurosis of musculotendinous junction (MTJ) in medial gastrocnemius (MG) head in a group of healthy individuals. The simulated and measured wave speed in gel constructs were in good agreement with a maximum error of 7.22%. The average of measured wave speed of fascia and aponeurosis was 3.90 ± 0.16 m/s and 2.33 ± 0.60 m/s, while the corresponding corrected shear modulus was 95.63 ± 17.89 kPa and 6.36 ± 8.98 kPa, respectively. Thickness had a substantial effect on the wave speed in thin-layered tissues with decreasing speed for thinner tissues. The SWE-based simulation method presented in this study has the potential of enhancing clinical assessment for several musculoskeletal conditions involving thin-layered tissues.

Which Confounders Have the Largest Impact in Shear Wave Elastography of Muscle and How Can They be Minimized? An Elasticity Phantom, Ex Vivo Porcine Muscle and Volunteer Study Using a Commercially Available System

The goal of the study was to investigate the quantitative impact of region of interest (ROI), software choice, muscle fiber orientation and preload tension on shear wave velocity (SWV). First, SWV was assessed in an isotropic elasticity phantom and ex vivo porcine muscle using a commercially available clinical ultrasound system. Secondly, SWV was acquired in relaxed and stretched calf muscles of healthy volunteers (dorsal extension of the talocrural joint), for both parallel and transverse probe direction to the fibers, as well as for different ROIs and software versions. The effect of intermediate probe-fiber alignments was also analyzed. Finally, the impact of confounding factors on SWV reproducibility was minimized with a second force-controlled volunteer study, in which the calf was isometrically loaded, and fiber orientation and ROI were well-defined. 2046 in vivoSWE images were acquired to analyze SWV reproducibility with different confounder settings. In healthy volunteers, the main variance-contributing factors were in order of importance muscle tension, fiber orientation, horizontal ROI size and insertion depth. Regression analysis showed significantly reduced SWV with increasing insertion depth for each study material. Parallel probe-fiber orientation, muscle stretch and increasing horizontal ROI size led to significantly higher SWV. Based on the results of the study, we provide recommendations to minimize the impact of confounders in musculoskeletal elastography and discuss the main confounding mechanisms and trade-offs between confounding variables. Coefficients of variation can be significantly reduced with a controlled protocol, if the confounders are clinically taken into account.

Reduction in stiffness of proximal leg muscles during the first 6 months of glucocorticoid therapy for giant cell arteritis: A pilot study using shear wave elastography

AIM

To investigate muscle stiffness changes in patients treated for giant cell arteritis (GCA) with high-dose oral glucocorticoids.

METHODS

Using ultrasound elastography, shear wave velocity (SWV) was measured in the quadriceps, hamstrings and biceps brachii muscles of 14 patients with GCA (4 male, mean age ± SD, 68.2 ± 4.3 years) within the first 2 weeks of initiating glucocorticoid treatment (baseline) and repeated after 3 and 6 months treatment. Muscle strength and performance tests were performed at each visit. Baseline measures were compared with those from 14 healthy controls. Linear mixed models were used to test for change in patient measures over time.

RESULTS

At baseline, muscle SWV in patients was not significantly different from controls. With glucocorticoid treatment, there was a reduction in SWV in the leg but not the arm muscles. SWV decreased by a mean of 14% (range 8.3%-17.3%; P = .001) after 3 months and 18% (range 10.2%-25.3%; P < .001) after 6-months in the quadriceps and hamstrings during the resting position. The baseline, 3 and 6 months mean SWV (±SD) for the vastus lateralis were 1.62 ± 0.16 m/s, 1.40 ± 0.10 m/s and 1.31 ± 0.06 m/s, respectively (P < .001). In the patient group as a whole, there was no significant change in muscle strength. However, there were moderate correlations (r = .54-.69) between exhibiting weaker muscle strength at follow-up visits and a greater reduction in SWV.

CONCLUSION

Glucocorticoid therapy in patients with GCA was associated with a significant reduction in proximal leg muscle stiffness during the first 6 months. Future research should study a larger sample of patients for a longer duration to investigate if diminished muscle stiffness precedes signs of glucocorticoid-induced myopathy.

Narrowband Shear Wave Generation Using Sinusoidally Modulated Acoustic Radiation Force

Most transient ultrasound elastography methods use high-intensity ultrasound "push" pulses that generate a shear wave with a wide frequency spectrum. However, it is difficult to control how the energy of the wave is distributed within that spectrum. For this reason, the shear-wave group velocity may not match that of harmonic methods like magnetic resonance elastography (MRE). The objective of this study was to introduce a narrowband shear wave generation method produced by "push" pulses with sinusoidally modulated intensity. The method, named harmonic shear wave imaging (HSWI), successively transmits a series of push pulses with a periodic change in duration. The excited shear waves form a continuous shear wave with a known main frequency that can be controlled by the user. Push pulses are interleaved with imaging pulses so only one clinical transducer is used to generate and record the shear waves. The proposed method was compared to MRE and a transient shear wave elastography method using phantoms and in vivo measurements. It was found that HSWI produces narrowband waves with a speed that closely matches that measured by MRE. Measurement of the acoustic output parameters indicated that the acoustic intensities in HSWI are suitable for clinical applications. The ability of HSWI to generate narrowband shear waves using a single linear array transducer makes it amenable for clinical translation. HSWI can potentially use the same thresholds as MRE for diagnosis of diseases affecting the stiffness of soft tissues.

Muscle shear wave elastography in idiopathic inflammatory myopathies: a case-control study with MRI correlation

OBJECTIVE

To investigate muscle stiffness in patients with idiopathic inflammatory myopathies (IIM) using shear wave elastography (SWE) and to correlate the results with muscle strength and MRI features of myositis.

MATERIALS AND METHODS

Muscle shear wave velocity (SWV) was measured in 23 active IIM patients (13 females, mean age 50.4 ± 16.1 years) and 23 matched healthy controls (13 females, mean age 50.7 ± 16.2 years). The investigated muscles included the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM) vastus intermedius (VI), biceps femoris (BF), semitendinosus (ST), semimembranosus (SM) and the biceps brachii (BB) scanned during relaxed resting and passive stretching positions. Participants performed multiple tests to evaluate their muscle strength. IIM patients had a thigh MRI to assess degrees of oedema, fatty infiltration and atrophy.

RESULTS

In the resting position, IIM patients had a 12.9-22.2% significantly lower SWV (p < 0.05) for the quadriceps and hamstrings, but not BB. There was no difference during passive stretching. The SWV for VL, VI and BF showed moderate correlations with the muscle strength tests ranging from r = 0.47 to r = 0.70 (all p < 0.05). Lower SWV was associated with greater MRI scores of oedema (p = 0.001) and atrophy (p = 0.006). However, SWV did not correlate with fatty infiltration (r < 0.3; p = 0.28), creatine kinase (r = 0.28; p = 0.19) or disease duration (r = 0.26; p = 0.24).

CONCLUSION

Shear wave elastography may detect abnormal reduced thigh stiffness in IIM patients. SWE measurements were significantly associated with muscle weakness and MRI signs of oedema and atrophy. Future research should investigate this new technology for monitoring disease activity.

Change in skeletal muscle stiffness after running competition is dependent on both running distance and recovery time: a pilot study

Long-distance running competitions impose a large amount of mechanical loading and strain leading to muscle edema and delayed onset muscle soreness (DOMS). Damage to various muscle fibers, metabolic impairments and fatigue have been linked to explain how DOMS impairs muscle function. Disruptions of muscle fiber during DOMS exacerbated by exercise have been shown to change muscle mechanical properties. The objective of this study is to quantify changes in mechanical properties of different muscles in the thigh and lower leg as function of running distance and time after competition. A custom implementation of Focused Comb-Push Ultrasound Shear Elastography (F-CUSE) method was used to evaluate shear modulus in runners before and after a race. Twenty-two healthy individuals (age: 23 ± 5 years) were recruited using convenience sampling and split into three race categories: short distance (nine subjects, 3–5 miles), middle distance (10 subjects, 10–13 miles), and long distance (three subjects, 26+ miles). Shear Wave Elastography (SWE) measurements were taken on both legs of each subject on the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), soleus, lateral gastrocnemius (LG), medial gastrocnemius (MG), biceps femoris (BF) and semitendinosus (ST) muscles. For statistical analyses, a linear mixed model was used, with recovery time and running distance as fixed variables, while shear modulus was used as the dependent variable. Recovery time had a significant effect on the soleus (p = 0.05), while running distance had considerable effect on the biceps femoris (p = 0.02), vastus lateralis (p < 0.01) and semitendinosus muscles (p = 0.02). Sixty-seven percent of muscles exhibited a decreasing stiffness trend from before competition to immediately after competition. The preliminary results suggest that SWE could potentially be used to quantify changes of muscle mechanical properties as a way for measuring recovery procedures for runners.