Quantitative Ultrasound Elastography With an Acoustic Coupler for Achilles Tendon Elasticity: Measurement Repeatability and Normative Values

Musculoskeletal ultrasound: a technical and historical perspective

During the past four decades, musculoskeletal ultrasound has become popular as an imaging modality due to its low cost, accessibility, and lack of ionizing radiation. The development of ultrasound technology was possible in large part due to concomitant advances in both solid-state electronics and signal processing. The invention of the transistor and digital computer in the late 1940s was integral in its development. Moore's prediction that the number of microprocessors on a chip would grow exponentially, resulting in progressive miniaturization in chip design and therefore increased computational power, added to these capabilities. The development of musculoskeletal ultrasound has paralleled technical advances in diagnostic ultrasound. The appearance of a large variety of transducer capabilities and rapid image processing along with the ability to assess vascularity and tissue properties has expanded and continues to expand the role of musculoskeletal ultrasound. It should also be noted that these developments have in large part been due to a number of individuals who had the insight to see the potential applications of this developing technology to a host of relevant clinical musculoskeletal problems. Exquisite high-resolution images of both deep and small superficial musculoskeletal anatomy, assessment of vascularity on a capillary level and tissue mechanical properties can be obtained. Ultrasound has also been recognized as the method of choice to perform a large variety of interventional procedures. A brief review of these technical developments, the timeline over which these improvements occurred, and the impact on musculoskeletal ultrasound is presented below.

Assessment of knee collateral ligament stiffness by strain ultrasound elastography

BACKGROUND: Knowledge of the biomechanics of the normal collateral ligaments is important to secure optimal stability of the knee following injury. Various in vitro methods have been described in evaluating the biomechanics of these ligaments. However, a method of direct evaluation has not been reported. OBJECTIVE: To determine the stiffness characteristics of the collateral ligaments of the knee using strain ultrasound elastography. METHODS: Strain ultrasound elastography was performed on different components of the collateral ligaments in various angles of knee flexion in 18 healthy males (36 ligaments). We measured relative stiffness of the ligaments using strain ratio (SR = target tissue strain/reference strain). A lower strain ratio indicates higher relative stiffness. RESULTS: There was moderate to excellent intra- and inter-rater agreement for strain ratio measurements in all ligament portions. Strain ratios were lowest at 0° in all three ligaments, indicating high relative stiffness. In the superficial and deep medial collateral ligaments, the strain ratio increased with increasing knee flexion, whereas in the lateral collateral ligament, stiffness showed a tendency to fluctuate. CONCLUSION: Strain ultrasound elastography is a reliable tool for monitoring relative stiffness of the collateral ligaments of the knee and is easily applied to the routine clinical setting.

HOW USEFUL IS ELASTOGRAPHY IN THE FOLLOW-UP OF ACHILLES TENDON REPAIR?

Introduction:

In addition to conservative modalities in the treatment of Achilles tendon injuries, open, percutaneous and minimally invasive semi-open techniques, as well as biological open surgical repair methods are used as surgical options. Compression elastography is one of the methods used for the follow-up of treatment in Achilles tendon injuries.

Methods:

23 patients were included in our study between July 2013 and June 2014, as long as they had at least 4 years of follow-up. In the final control, the intact side and the operated side were both examined and compared. The variables were the American Orthopedic Foot and Ankle Score (AOFAS) which is measured as a functional score considering plantar flexion and dorsiflexion; calf circumference; Achilles tendon anteroposterior (AP) diameter; and elastographic examination.

Results:

The strain ratio value and AP diameter of the patients was significantly higher on the operated side than on the non-operated side (p <0.001). There was no significant difference between the plantar flexion and dorsiflexion degrees on the operated side of the patients(p> 0.05). No correlation was observed between strain ratio and AOFAS (p: 0,995).

Conclusion:

Elastography is not a useful technique to evaluate functional results on long-term tendon healing. Level of Evidence III; Retrospective comparative study.

In vivo stiffness assessment of patellar and quadriceps tendons by strain ultrasound elastography

BACKGROUND:

The patellar and quadriceps tendons are responsible for the extension mechanism of the knee joint and frequently become inflamed during sports. Diagnosis and determination of when an athlete can return to sports following these injuries are usually performed by assessing morphological features and functional outcomes. Nevertheless, mechanical properties are not being assessed.

OBJECTIVE:

To describe the stiffness characteristics of these two tendons over the range of knee flexion and to test the feasibility of using strain ultrasound elastography (SE).

METHODS:

SE with an acoustic coupler as the reference was performed for nine healthy males. Relative stiffness measurements were obtained using the strain ratio (SR = target tissue strain/reference strain) by placing the knee in five different flexion angles. Lower SR indicates higher relative stiffness.

RESULTS:

This study showed reliable measurement with good intra- and inter-rater agreement for SR at 30°. SR of the quadriceps tendon decreases as knee flexion increases, indicating increased relative stiffness. In the patellar tendon, no significant difference was observed between 30° and 60°. Beyond 60°, relative stiffness increased constantly.

CONCLUSIONS:

SE is a reproducible and feasible tool to monitor relative stiffness of the patellar and quadriceps tendons in routine clinical settings.

Medial Ankle Stability Evaluation With Dynamic Ultrasound: Establishing Natural Variations in the Healthy Cohort

INTRODUCTION

Destabilizing injuries to the deltoid ligament have relied on radiographic stress examination for diagnosis, with a focus on medial clear space (MCS) widening. Recently, studies have demonstrated the use of ultrasonography to assess deltoid ligament injury, but not the medial ankle stability. The purpose of this study was to assess the MCS via ultrasonography while weight-bearing and with a gravity stress test (GST) in the uninjured ankle as a means of establishing normative values for future comparison.

METHODS

Twenty-six participants with no reported ankle injury in their premedical history were included. The MCS was examined using ultrasonography with the patient lying in a lateral decubitus position to replicate a GST with the ankle held in a neutral and plantarflexed position as well as while weight-bearing. The MCS was assessed in mm at the anteromedial and inferomedial aspect of the ankle joint.

RESULTS

With weight-bearing, the average anterior MCS and inferior MCS were 3.6 and 3.3 mm, respectively. During the GST in neutral ankle position, the average anterior MCS was 4.1 mm, whereas the average inferior MCS was 4.0 mm. When measured during the GST in plantarflexed ankle position, the averages anterior MCS and inferior MCS increased to 4.4 mm. MCS values were notably higher with GST than with weight-bearing measurements (P < 0.001). MCS values were notably higher with the foot in a plantarflexed compared with a neutral position when doing GST (P < 0.001). No notable differences in MCS distance were found when comparing laterality (P > 0.05). Height had a notable effect on all MCS values (P < 0.05). Inter- and intra-rater reliabilities for ultrasonographic MCS measurements were all excellent (interclass correlation coefficient >0.75).

DISCUSSION

Ultrasound can reliably measure the MCS of the ankle while doing dynamic stress manoeuvres. With the deltoid ligament intact, a GST increases MCS widening more than weight-bearing, and holding the ankle in plantarflexion while doing a gravity stress view, further increases this difference.

LEVELS OF EVIDENCE

Diagnostic studies-investigating a diagnostic test: Level III.

Ultrasound Evaluation of the Rectus Femoris for Sarcopenia in Patients with Early Subacute Stroke

We investigated the ultrasound characteristics of the rectus femoris for sarcopenia detected by dual-energy X-ray absorptiometry (DEXA) in the early subacute stroke phase. Physical features (age, sex, body mass index, and circumference of thigh) and performances (modified Barthel index in Korean, functional ambulation categories, and mini-mental state examination in Korean) were measured. The thickness of the fat layer, the thickness of the rectus femoris (TRF), echo intensity (EI), EI to TRF ratio, and strain ratio of elastography (SRE) were measured by ultrasound in 30 patients with first-ever stroke (male: n = 20). Appendicular lean body mass was measured by DEXA. Sarcopenia was defined according to the Foundation for the National Institutes of Health Sarcopenia Project. In total, 14 patients were in the sarcopenia group, and 16 were in the non-sarcopenia group. Clinical characteristics were similar between the two groups. In the sarcopenia group, TRF was significantly decreased in the paretic (p < 0.026) and non-paretic sides (p < 0.01), and the EI to TRF ratio on the paretic side was significantly increased (p < 0.049). Multivariate binary logistic regression showed that TRF on the non-paretic side was independently and significantly associated with sarcopenia (OR = 0.616, 95% CI: 0.381-0.996). The EI and SRE were not significant between the two groups. In the early subacute stroke phase, TRF on the non-paretic side is a key factor for quantitative evaluation of sarcopenia, and the EI to TRF ratio on the paretic side is also a meaningful qualitative evaluation of sarcopenia.

Reliability of Sonoelastography Measurements of Lower Limb Tendon Properties: A Systematic Review

This study investigated the reliability of sonoelastography techniques in quantifying lower limb tendon elasticity. A literature search was conducted using PubMed, Web of Science and CINAHL. The quality of the selected papers was evaluated using the Guidelines for Reporting Reliability and Agreement Studies and the Quality Appraisal Tool for Studies of Diagnostic Reliability checklist. Reliability values were extracted and synthesized. Twenty-four studies were included and were divided by the two main technologies used: strain and shear-wave elastography. The overall methodological quality was questionable; all studies were at risk of bias. Highly variable results ranging from poor to excellent reliability were found for both technologies and for all tendons considered. Intra-rater reliability of strain elastography on the Achilles tendon and shear-wave elastography on the patellar and quadriceps tendon was adequate. Inter-rater, inter-session and inter-machine reliability was insufficient. Caution should be used when interpreting results from sonoelastography studies measuring lower limb tendon elasticity.

Ulnar Collateral Ligament Laxity After Repetitive Pitching: Associated Factors in High School Baseball Pitchers

BACKGROUND

Medial elbow injury is common in baseball pitchers, with evidence of elbow valgus instability after only 60 consecutive pitches. However, the tissue-specific effects of repetitive pitching on medial elbow stabilizers are largely unknown.

PURPOSE/HYPOTHESIS

This study aimed to investigate changes in the ulnar collateral ligament (UCL) and forearm flexor-pronator muscles (FPMs) during repetitive pitching and factors that relate to identified change. We hypothesized that repetitive pitching would increase elasticity of the medial elbow stabilizers and therefore induce laxity.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A total of 30 high school baseball pitchers participated (mean ± SD age, 16.6 ± 0.5 years). Each participant pitched 100 times (5 blocks of 20 pitches). The strain ratio, indicating elasticity in the UCL and FPMs, was measured using ultrasound before pitching and after every 20-pitch block. Data for each pitch block were compared using analysis of variance. Multiple regression analysis was used to investigate factors related to the change rate of the strain ratio.

RESULTS

The strain ratio of the UCL after 100 pitches was significantly less than that before pitching (before pitching, 4.83 ± 1.70; after 100 pitches, 3.59 ± 1.35; P = .013), but this was not the case for the FPMs (before pitching, 0.57 ± 0.24; after 100 pitches, 0.43 ± 0.18; P = .07). The ratio of the strain ratio in the UCL and FPMs (UCL/FPMs) before pitching (β = -0.385; P = .031) and the elbow flexion range of motion before pitching (β = -0.352; P = .046) were significantly and independently correlated with the change rate of the UCL.

CONCLUSION

Elasticity significantly increased for the UCL, indicating laxity, but not for the FPMs after 100 pitches. Furthermore, the ratio of elasticity (UCL/FPMs) and the elbow flexion range of motion before pitching were significantly related to the change rate of UCL elasticity.

CLINICAL RELEVANCE

To reduce laxity of the UCL, pitchers should be limited to <100 pitches per game. Sustaining a lower level of relative FPMs to UCL elasticity at rest and maintaining a large muscle volume to avoid excessive elbow flexion range of motion may prevent UCL laxity that develops during repetitive pitching.

Measuring stiffness of normal medial collateral ligament in healthy volunteers via shear wave elastography

PURPOSE

We aim to determine a reference data set for normal medial collateral ligament (MCL) stiffness values using shear wave elastography (SWE).

METHODS

Quantitative stiffness of the MCL was measured at three levels: the proximal (MCL area from the level of the medial meniscus to the level of the femoral attachment), the middle (MCL area at the level of the medial meniscus), and the distal (MCL area from the level of the medial meniscus to the level of the tibial attachment) segments of the MCL at a knee position of 0°.

RESULTS

A total of 60 MCL of 30 healthy volunteers (15 female, 15 male) were examined. The mean stiffness values of the proximal, middle, and distal MCL for observer 1 were 32.25 ± 6.44, 34.25 ± 6.84, and 35.47 ± 6.98, respectively. The mean stiffness values of the proximal, middle, and distal MCL for observer 2 were 33.56 ± 6.76, 35.44 ± 6.91, and 36.32 ± 7.04, respectively.

CONCLUSION

SWE has a strong potential to be a method of choice for evaluating MCL stiffness. Our study participants were healthy volunteers and the data can be used as reference data for future studies.

Evaluation of the Achilles Tendon Using B-Mode Ultrasound and Strain Elastography in Patients With Chronic Kidney Disease

OBJECTIVES

To investigate the B-mode ultrasound (US) features and elasticity of the Achilles tendon in patients with chronic kidney disease (CKD) using US elastography and to compare them with those of healthy individuals.

METHODS

From March 2019 through May 2019, 30 consecutive patients with variable stages of CKD and 30 healthy individuals were prospectively included in this study. Ultrasound and strain elastographic examinations were performed on both Achilles tendons of all individuals. Degrees of tendinopathy, if existed, were classified as defined by Archambault et al (J Clin Ultrasound 1998; 26:335-339), and thicknesses were documented with US. Strain ratios (SRs) were calculated by measuring the strain values from the Achilles tendon and Kager fat pad. Statistical differences in the SRs of Achilles tendons between the control group and patients with CKD were calculated.

RESULTS

The 30 patients with CKD ranged in age from 24 to 73 years, and the 30 healthy individuals ranged in age from 25 to 78 years. Both distal and left middle thirds of the Achilles tendons were thicker in patients with CKD than in healthy individuals (P < .05). The mean SRs ± SDs in the patient group (4.71 ± 0.95 and 4.85 ± 1.47 on the right and left, respectively) were significantly higher (P < .05) than in healthy individuals (2.31 ± 0.42 and 2.65 ± 0.55 on the right and left), which indicated an increased stiffness of Achilles tendons in the patient group.

CONCLUSIONS

As a semiquantitative and noninvasive imaging modality, strain elastography has the potential to detect the morphologic and elasticity changes of Achilles tendons in patients with CKD, which may give an opportunity to help physicians predict possible leading partial or complete tears.

Shear wave and strain sonoelastography for the evaluation of the Achilles tendon during isometric contractions

Objectives

Changes in mechanical loading as well as pathology can modify the Achilles tendon mechanical properties and therefore detection of these changes is relevant for the diagnosis and management of Achilles tendinopathy. The aim of this study was to evaluate strain and shear wave sonoelastography for their ability to detect changes in the Achilles tendon mechanical properties during a series of isometric contractions.

Methods

Longitudinal sonoelastography images of the Achilles tendon were acquired from 20 healthy participants using four different ultrasound devices; two implementing strain sonoelastography technology (SE1, SE2) and two, shear wave elastography technology (SWE1, SWE2).

Results

SE1 measured a decreasing strain ratio (tendon become harder) during the different contraction levels from 1.51 (0.92) to 0.33 (0.16) whereas SE2 mesaured a decreasing strain ratio from 1.08 (0.76) to 0.50 (0.32). SWE1 measured decreasing tendon stiffness during contractions of increasing intensity from 33.40 (19.61) to 16.19 (2.68) whereas SWE2 revealed increasing tendon stiffness between the first two contraction levels from 428.65 (131.5) kPa to 487.9 (121.5) kPa followed by decreasing stiffness for the higher contraction levels from 459.35 (113.48) kPa to 293.5 (91.18) kPa.

Conclusions

Strain elastography used with a reference material was able to detect elasticity changes between the different contraction levels whereas shear wave elastography was less able to detect changes in Achilles tendon stiffness when under load. Inconsistent results between the two technologies should be further investigated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13244-021-00974-y.

Sonoelastography of Normal Canine Common Calcaneal Tendon: Preliminary Results

Shear wave elastography (SWE) is a feasible and newly developed ultrasonographic technique which is able to assess elasticity of tissues. The aim of this work was to assess the feasibility of SWE on the normal canine common calcaneal tendon (CCT) evaluating the intra-operator repeatability and reproducibility of single measurements and stiffness of different anatomic CCT portions was examined. Tendons were first evaluated with B-mode ultrasound with a linear probe 8.5 to 10 MHz in longitudinal section with slight flexed tarsocrural joint and a gel-pad. Common calcaneal tendon was divided into three different anatomical regions. Shear wave elastography was performed in each region by two operators and quantitative evaluation (m/s and kPa) was performed on the most representative images. Region of interest (0.15 cm) was settled. Intraclass correlation coefficient (ICC) results were classified using the following scale: 0.00 to 0.20 = poor; 0.20 to 0.40 = fair; 0.40 to 075 = good; >0.75 = excellent. Ten adult dogs were enrolled. Intra-operator ICC values were >0.75 for both operators in every tendon portion. Inter-operator SWE ICC values for m/s measurements were 0.3, 0.61 and 0.61 for the enthesis, intermediate portion and the myotendinous junction respectively; for kPa measurements, values were respectively 0.3, 0.7 and 0.81. The three CCT portions were significantly different in stiffness (p-value < 0.001 for both m/s and kPa measurements). These preliminary results provide evidence that SWE is potentially appliable to assess mechanical properties of canine CCT affected by tendinopathies.

Toward Quantitative and Operator-independent Quasi-static Ultrasound Elastography: An Ex Vivo Feasibility Study

It is known that the elasticity of liver reduces progressively in the case of diffuse liver disease. Currently, the diagnosis of diffuse liver disease requires a biopsy, which is an invasive procedure. In this paper, we evaluate and report a noninvasive method that can be used to quantify liver stiffness using quasi-static ultrasound elastography approach. Quasi-static elastography is popular in clinical applications where the qualitative assessment of relative tissue stiffness is enough, whereas its potential is relatively underutilized in liver imaging due to lack of local stiffness contrast in the case of diffuse liver disease. Recently, we demonstrated an approach of using a calibrated reference layer to produce quantitative modulus elastograms of the target tissue in simulations and phantom experiments. In a separate work, we reported the development of a compact handheld device to reduce inter- and intraoperator variability in freehand elastography. In this work, we have integrated the reference layer with a handheld controlled compression device and evaluate it for quantitative liver stiffness imaging application. The performance of this technique was assessed on ex vivo goat liver samples. The Young's modulus values obtained from indentation measurements of liver samples acted as the ground truth for comparison. The results from this work demonstrate that by combining the handheld device along with reference layer, the estimated Young's modulus value approaches the ground truth with less error compared with that obtained using freehand compression (8% vs. 15%). The results suggest that the intra- and interoperator reproducibility of the liver elasticity also improved when using the handheld device. Elastography with a handheld compression device and reference layer is a reliable and simple technique to provide a quantitative measure of elasticity.

Strain Ultrasound Elastography in the Achilles Tendon of Ankylosing Spondylitis Patients Treated With Anti-TNF-α: A Preliminary Study

BACKGROUND/AIM

To compare patients affected by ankylosing spondylitis (AS) treated with anti-TNF-α for two years with controls in terms of Achilles tendon stiffness, ultrasound structure and thickness.

PATIENTS AND METHODS

B-mode ultrasound evaluation and strain ultrasound elastography were performed in longitudinal and transverse planes on 22 Achilles tendons of 11 AS patients and 26 of 13 controls.

RESULTS

There were no significant differences in thickness and stiffness of the Achilles tendon between AS patients and controls, except for an increased thickness in the middle third of the tendon in the AS patients (p=0.04). The Achilles tendon stiffness ratio of AS patients was 1.02±0.36 vs. 1.14±0.38 in the controls (p=0.2).

CONCLUSION

AS patients had an Achilles tendon thickness greater than controls at the middle third, but no difference in the stiffness was found among them. Strain ultrasound elastography may be useful to exclude early changes in mechanical properties of tendons.

Quantitative quasi-static ultrasound elastography using reference layer: Ex-vivo study

It is well-documented in the literature that changes in tissue elasticity are generally correlated with disease condition. In the case of diffuse liver disease, the elasticity of the liver reduces progressively. However, this change does not clearly manifest in conventional ultrasound examinations. Although quasi-static elastography is popular in clinical applications where qualitative assessment of relative tissue stiffness is enough, its potential is relatively underutilized in liver imaging due to the need for quantitative stiffness value. Recently, it was demonstrated that using a reference layer of known stiffness, one could produce quantitative modulus elastograms of the target tissue using quasi-static elastography using simulations and phantom experiments. Here, we examined the performance of this approach on ex-vivo goat liver samples and compare the estimated modulus values to that obtained from indentation measurements. The results suggest that using this approach of reference layer yields Young's modulus values within 10% error compared to the ground truth.

A novel application of strain sonoelastography can detect changes in Achilles tendon elasticity during isometric contractions of increasing intensity

Background

Mechanical and morphological properties of the Achilles tendon are altered in disease and in response to changes in mechanical loading. In the last few years different ultrasound based technologies have been used to detect tendon mechanical properties changes mainly in resting condition. Therefore the aim of this study was to evaluate if strain sonoelastography can identify changes in Achilles tendon elasticity during isometric contractions of increasing intensity.

Methods

This cross-sectional study enrolled 37 healthy volunteers (19 women) with mean (±SD) age of 27.1 (±7.0) years between January and June 2017. Strain sonoelastography images of the Achilles tendon were acquired during an isometric ramp force (0 kg, 0.5 kg, 1 kg, 2 kg, 5 kg and, 10 kg). An external reference material was used to provide a comparison between the examined tissue and a material of constant elasticity. Friedman test with post hoc pairwise comparison were used to determine the correlation between the difference contraction levels.

Results

The median and interquartile range (IQR) values for the strain ratio were 1.61 (1.5–2.9) in a relaxed state and 1.30 (1.07–2.02), 1.00 (0.76–1.66), 0.81 (0.70–1.19), 0.47 (0.39–0.73) and 0.33 (0.28–0.40) for 0.5 kg, 1 kg, 2 kg, 5 kg and 10 kg, respectively revealing increased tendon hardness with increasing contraction intensities. Friedman test revealed significant differences (p < 0.05) in the strain ratio between all contractions except between 0.5 kg – 1 kg (p = 0.41); 1 kg – 2 kg (p = 0.12) and 5 kg – 10 kg (p = 0.12).

Conclusion

Strain sonoelastography can detect changes in Achilles tendon elasticity between different contraction intensities. The results provide an original force-elasticity curve for the Achilles tendon in a healthy, asymptomatic population.

Trial registration

The study was approved by the Ethics Committee of Canton Ticino.

Ultrasonic strain elastography for detecting abnormalities in the supraspinatus tendon: an intra- and inter-rater reliability study

OBJECTIVES

The reliability of ultrasonic strain elastography (SEL) used to detect abnormalities in the supraspinatus tendon is unclear. Thus, the aim of this study was to investigate the reliability of SEL in the supraspinatus tendon.

DESIGN

An intra-rater and inter-rater reliability study.

SETTING

A single-centre study conducted at the University of Southern Denmark.

PARTICIPANTS

Twenty participants with shoulder pain and MRI-verified supraspinatus tendinosis and 20 asymptomatic participants (no MRI).

PRIMARY AND SECONDARY OUTCOME MEASURES

Raw values (RAW) and ratios (deltoid muscle (DELT) and gel pad (GEL) as reference tissues) were calculated and mean values of measurements from three regions of the supraspinatus tendon were reported. Colour scale ratings and number of yellow/red lesions from the three areas were also included.

RESULTS

Intra-rater reliability showed intraclass correlation coefficients (ICCs) for RAW, DELT and GEL: 0.97 (minimal detectable change (MDC): 0.28 (6.36% of the mean)), 0.89 (MDC: 2.91 (20.37%)) and 0.73 (MDC: 1.61 (58.82%)), respectively. The ICCs for inter-rater reliability were 0.89 (MDC: 0.47 (10.53%)), 0.78 (MDC: 3.69 (25.51%)) and 0.70 (MDC: 1.75 (62.63%)), respectively.For colour scale ratings, intra-rater reliability (linear weighted kappa) ranged from 0.76 to 0.79, with the inter-rater reliability from 0.71 to 0.81. For the number of lesions, intra-rater reliability ranged from 0.40 to 0.82 and inter-rater reliability from 0.24 to 0.67.

CONCLUSIONS

Intra-rater and inter-rater reliability were excellent for raw values and for ratios with deltoid muscle as the reference tissue, and good for ratios with gel pad as the reference tissue. The reliability of colour scale ratings was substantial-to-almost perfect, and for the number of lesions fair-to-almost perfect.Although high reliability was found, validity and responsiveness of these elastographic methods needs further investigation.

ETHICS APPROVAL

The study protocol was approved by the Ethics Committee for the Region of South Denmark (S-20160115) and reported to the Danish Data Protection Agency (2014-41-3266).

Real-time ultrasound elastography evaluation of achilles tendon properties in patients with mild hemiplegic stroke after rehabilitation training

OBJECTIVE

This study aims to evaluate the Achilles tendon's properties after rehabilitation training in patients with stroke using real-time ultrasound elastography.

METHODS

A total of 24 patients with mild hemiplegic stroke in the past 6 to 12 months and unilateral lower limb movement disorder were prospectively enrolled. All patients accepted 9-week rehabilitation training with the same schema. The 2-dimensional elastography and real-time elastography findings in the impaired and contralateral normal Achilles tendon were measured at pretraining and at 3, 6, and 9 weeks after training, which included tendon length, thickness, elasticity score (grade 1-3), and strain ratio of fat to tendon. The functional properties, which include the 10-meter walk test and timed up-and-go scores, were evaluated before and after the 9-week training.

RESULTS

The impaired Achilles tendon had a longer length (P = .002), lower frequency of grade 1 (P = .012), and lower strain ratio (P = .009) than the contralateral tendon before training. The impaired tendons at the third, sixth, and ninth weeks after training were compared to ones before training, respectively, which revealed shorter length, increased frequency of grade 1, and increased strain ratio. The first statistically significant changes in the length were observed at the sixth week, while such changes in elasticity score and strain ratio were observed at the ninth week.

CONCLUSIONS

Two-dimensional elastography and real-time elastography can provide valuable imaging markers for quantitatively evaluating the Achilles tendon's properties after rehabilitation training in patients with stroke.

Towards quantitative quasi-static ultrasound elastography using a reference layer for liver imaging application: A preliminary assessment

Changes in tissue elasticity are generally correlated with pathological phenomena. For example, diffuse liver disease progressively reduces the elasticity of the liver. Quasi-static elastography is popular in clinical applications to visualize regions with different relative stiffness. However, the limitation of this technique is that it provides only qualitative information. To overcome this, we investigate the use of a calibrated reference layer, sandwiched between the transducer and the tissue surface, to quantitatively image the unknown modulus of the examined tissue. The performance of the method was studied through simulations and experiments on agar-gelatin phantoms having Young's modulus within a range appropriate for the liver application. Furthermore, we explored the translational capability of the proposed method to work with existing commercially-available ultrasound scanners having elastography option. The Young's modulus value of the phantom estimated from quantitative elastography in simulation and experiment was compared against the corresponding ground-truth modulus value obtained from COMSOL and Universal Testing Machine (UTM) results, respectively. The results obtained for the compressive elastic modulus of the underlying phantom using quasi-static ultrasound elastography was found to be within 6% and 11% in simulation and experiments, respectively, to the corresponding ground-truth values.

A Multicenter Large-Sample Shear Wave Ultrasound Elastographic Study of the Achilles Tendon in Chinese Adults

OBJECTIVES

The changes in the viscoelasticity of the Achilles tendon are related to tendinopathy. Therefore, constructing a data model in the healthy population is essential to understanding the key factors affecting the viscoelasticity of the Achilles tendon. The purpose of our research was to obtain large sample data, construct a data model, and determine parameters that affect the elastic modulus of the Achilles tendon in healthy Chinese adults.

METHODS

We designed a prospective multicenter clinical trial to evaluate the viscoelasticity of the Achilles tendon by using shear wave elastography. A total of 1165 healthy adult participants from 17 Chinese hospitals were recruited for the assessment. The necessary parameters (age, height, weight, and body mass index) were recorded. The elastic modulus (Young modulus) was obtained from the middle of the Achilles tendon and calculated with feet in naturally relaxed, dorsal, and plantar positions. The thickness and perimeter of the Achilles tendon were measured via cross section on the same site. A multiple linear regression was performed to find the key factors affecting the Young modulus of the Achilles tendon.

RESULTS

The Young modulus of the left Achilles tendon in the natural relaxed position followed a normal distribution (P > .05) with a mean ± SD of 374.24 ± 106.12 kPa. The regression equations showed a positive correlation between the Young modulus and weight and a negative correlation between the Young modulus and the circumference or thickness of the left Achilles tendon (P < .05).

CONCLUSIONS

The Young modulus of the Achilles tendon as measured by shear wave elastography is related to body weight as well as the perimeter or thickness of the tendon.

Ultrasound elastography: compression elastography and shear-wave elastography in the assessment of tendon injury

Ultrasound elastography (USE) is a recent technology that has experienced major developments in the past two decades. The assessment of the main mechanical properties of tissues can be made with this technology by characterisation of their response to stress. This article reviews the two major techniques used in musculoskeletal elastography, compression elastography (CE) and shear-wave elastography (SWE), and evaluates the studies published on major electronic databases that use both techniques in the context of tendon pathology. CE accounts for more studies than SWE. The mechanical properties of tendons, particularly their stiffness, may be altered in the presence of tendon injury. CE and SWE have already been used for the assessment of Achilles tendons, patellar tendon, quadriceps tendon, epicondylar tendons and rotator cuff tendons and muscles. Achilles tendinopathy is the most studied tendon injury with USE, including the postoperative period after surgical repair of Achilles rupture tendon. In relation to conventional ultrasound (US), USE potentially increases the sensitivity and diagnostic accuracy in tendinopathy, and can detect pathological changes before they are visible in conventional US imaging. Several technical limitations are recognised, and standardisation is necessary to ensure repeatability and comparability of the results when using these techniques. Still, USE is a promising technique under development and may be used not only to promote an early diagnosis, but also to identify the risk of injury and to support the evaluation of rehabilitation interventions. KEY POINTS: • USE is used for the assessment of the mechanical properties of tissues, including the tendons. • USE increases diagnostic performance when coupled to conventional US imaging modalities. • USE will be useful in early diagnosis, tracking outcomes and monitoring treatments of tendon injury. • Technical issues and lack of standardisation limits USE use in the assessment of tendon injury.

Motorizing and Optimizing Ultrasound Strain Elastography for Detection of Intrauterine Growth Restriction Pregnancies

Intrauterine growth restriction is a prevalent disease in pregnancy in which placental insufficiency leads to 5 to 10 times higher mortality and lifelong morbidities. The current detection rate is poor, and recently, ultrasound strain elastography (USEL) was proposed as a new diagnostic technique. Currently, placental USEL uses maternal subcutaneous fat as the reference layer, but this is not ideal as fat tissue stiffness can vary widely between subjects. Current USEL also uses manual palpation, and under different compression depths and rates, viscoelastic tissues such as placenta can yield different stiffness results. In the study described here, we strove to improve placental USEL by (i) using an external polymeric pad of known stiffness as the reference layer and (ii) adopting motorized control of the transducer during USEL to standardize palpation motion. Results indicated that motorized USEL reduced measurement variability by 67% compared with freehand USEL. Satisfactory and statistically significant correlations between USEL measurements and mechanical testing validation results were obtained for our new USEL protocol. Placental tissues were found to be non-linear and viscoelastic in nature and, thus, differed in stiffness at different compression rates and depths. Our study also revealed that there was a specific compression depth and rate during USEL that provided better correlation to mechanical testing, and should be considered in clinical placental USEL.

Real-time sonoelastography: principles and clinical applications in tendon disorders. A systematic review

Background

Sonoelastography (SE) is a new ultrasound-based method adopted in an increased number of scientific reports to analyse normal and pathological tendons. The aim of this study is to provide a systematic overview of clinical applications of SE in normal and pathological tendons.

Methods

A systematic research of PubMed, Ovid, and Cochrane Library electronic databases was performed according to PRISMA guideline. Two Authors searched and evaluated the articles independently; a third Author was involved to solve any disagreement. The Oxford Level of Evidence (LoE) was used to assess each article.

Results

There is an increasing interest in the application of SE in the evaluation of healthy and diseased tendons. Many different tendons are amenable for SE evaluation, such as the Achilles and patellar tendons, rotator cuff, common extensor tendons, quadriceps tendon, and the plantar fascia.

Conclusion

SE appears to be a very useful diagnostic tool, in particular in tendon pathology. This is a dynamic examination, provides an immediate evaluation of the tissue elasticity, and may be useful in recognizing tendon abnormalities and in implementing the information available with conventional US.

Level of evidence

IV.

Poor reproducibility of compression elastography in the Achilles tendon: same day and consecutive day measurements

OBJECTIVE

To determine the reproducibility of compression elastography (CE) when measuring strain data, a measure of stiffness of the human Achilles tendon in vivo, over consecutive measures, consecutive days and when using different foot positions.

MATERIALS AND METHODS

Eight participants (4 males, 4 females; mean age 25.5 ± 2.51 years, range 21-30 years; height 173.6 ± 11.7 cm, range 156-189 cm) had five consecutive CE measurements taken on one day and a further five CE measures taken, one per day, at the same time of day, every day for a consecutive 5-day period. These 80 measurements were used to assess both the repeatability and reproducibility of the technique. Means, standard deviations, coefficient of variation (CV), Pearson correlation analysis (R) and intra-class correlation coefficients (ICC) were calculated.

RESULTS

For CE data, all CVs were above 53%, R values indicated no-to-weak correlations between measures at best (range 0.01-0.25), and ICC values were all classified in the poor category (range 0.00-0.11). CVs for length and diameter measures were acceptably low indicating a high level of reliability.

CONCLUSIONS

Given the wide variation obtained in the CE results, it was concluded that CE using this specific system has a low level of reproducibility for measuring the stiffness of the human Achilles tendon in vivo over consecutive days, consecutive measures and in different foot positions.

Quantitative US Elastography Can Be Used to Quantify Mechanical and Histologic Tendon Healing in a Rabbit Model of Achilles Tendon Transection

Purpose To determine the time-dependent change in strain ratios (SRs) at the healing site of an Achilles tendon rupture in a rabbit model of tendon transection and to assess the correlation between SRs and the mechanical and histologic properties of the healing tissue. Materials and Methods Experimental methods were approved by the institutional animal care and use committee. The Achilles tendons of 24 New Zealand white rabbits (48 limbs) were surgically transected. The SRs of Achilles tendons were calculated by using compression-based quantitative ultrasonographic elastography measurements obtained 2, 4, 8, and 12 weeks after transection. After in vivo elastography, the left Achilles tendon was harvested for mechanical testing of ultimate load, ultimate stress, elastic modulus, and linear stiffness, and the right tendons were harvested for tissue histologic analysis with the Bonar scale. Time-dependent changes in SRs, mechanical parameters, and Bonar scale scores were evaluated by using repeated-measures analysis of variance. The correlation between SRs and each measured variable was evaluated by using the Spearman rank correlation coefficient. Results Mean SRs and Bonar scale values decreased as a function of time after transection, whereas mechanical parameters increased (P < .001). SR correlated with ultimate stress (ρ = 0.68, P <.001,) elastic modulus (ρ = 0.74, P <.001), and the Bonar scale (ρ = 0.87, P <.001). Conclusion Quantitative elastography could be a useful method with which to evaluate mechanical and histologic properties of the healing tendon. ^© RSNA, 2017 Online supplemental material is available for this article.