Shear Wave Elastography System Research Articles

The role of shear viscosity as a biomarker for improving chronic kidney disease detection using shear wave elastography: A computational study using a validated finite element model

The application of ultrasound shear wave elastography for detecting chronic kidney disease, namely renal fibrosis, has been widely studied. A good correlation between tissue Young’s modulus and the degree of renal impairment has been established. However, the current limitation of this imaging modality pertains to the linear elastic assumption used in quantifying the stiffness of renal tissue in commercial shear wave elastography systems. As such, when underlying medical conditions such as acquired cystic kidney disease, which may potentially influence the viscous component of renal tissue, is present concurrently with renal fibrosis, the accuracy of the imaging modality in detecting chronic kidney disease may be affected. The findings in this study demonstrate that quantifying the stiffness of linear viscoelastic tissue using an approach similar to those implemented in commercial shear wave elastography systems led to percentage errors as high as 87%. The findings presented indicate that use of shear viscosity to detect changes in renal impairment led to a reduction in percentage error to values as low as 0.3%. For cases in which renal tissue was affected by multiple medical conditions, shear viscosity was found to be a good indicator in gauging the reliability of the Young’s modulus (quantified through a shear wave dispersion analysis) in detecting chronic kidney disease. The findings show that percentage error in stiffness quantification can be reduced to as low as 0.6%. The present study demonstrates the potential use of renal shear viscosity as a biomarker to improve the detection of chronic kidney disease.

Validation of the Baveno VI criteria to rule out high-risk varices using hepatic shear-wave elastography.

Liver stiffness measurement (LSM) by transient elastography has been validated to predict high-risk varices (HRV). We aimed to evaluate the accuracy of shear-wave elastography (SWE) and platelet count (Baveno VI criteria) to rule out HRV in patients with compensated advanced chronic liver disease (c-ACLD). This retrospective study analyzed data of patients with c-ACLD (transient elastography ≥ 10 kPa) submitted to two-dimensional SWE (2D-SWE) (GE-LOGIQ-S8) and/or point SWE (p-SWE) (ElastPQ) who had a gastrointestinal endoscopy within 24 months. HRV definition was a large size and presence of red wale marks or sequelae from previous treatment. Optimal thresholds of SWE systems for HRV were identified. The proportion of spared gastrointestinal endoscopies and missing HRV considering a favorable SWE Baveno VI criteria were assessed. Eighty patients [36% male, median age = 63 (interquartile range, 57-69) years] were included. The prevalence of HRV was 34% ( n = 27/80). The optimal thresholds to predict HRV were 10 kPa and 12 kPa for 2D-SWE and p-SWE, respectively. A favorable 2D-SWE Baveno VI criteria (LSM < 10 kPa and platelets count > 150 × 10 9 /mm 3 ) avoided 19% of gastrointestinal endoscopies without missing HRVs. A favorable p-SWE Baveno VI criteria (LSM < 12 kPa and platelets count > 150 × 10 9 /mm 3 ) spared 20% of gastrointestinal endoscopy without missing HRVs. Using a lower threshold of platelet count (<110 × 10 9 /mm 3 , expanded Baveno VI), 2D-SWE (<10 kPa) avoided 33% of gastrointestinal endoscopy with 8% of missing HRVs, while p-SWE (<12 kPa) avoided 36% of gastrointestinal endoscopy with 5% of missing HRVs. LSM by p-SWE or 2D-SWE combined with platelet count (Baveno VI criteria) can spare a considerable number of gastrointestinal endoscopies missing a negligible proportion of HRV.

P 73 Muscle relaxation in myotonia and longitudinal nerve mobility in carpal tunnel syndrome as possible clinical applications for “dynamic” ultrasound shear-wave elastography

Shear wave elastography (SWE) is an emerging modality in clinical ultrasound. Using acoustic radiation force impulses to generate transversal shear waves and fast imaging to track their propagation, it enables the non-invasive estimation of two-dimensional maps of tissue elasticity. Various applications in neuromuscular medicine have been investigated, e.g., altered muscle elasticity has been reported in muscular dystrophy and inflammatory myopathies, and elasticity of the median nerve at the wrist has been shown to be increased in carpal tunnel syndrome. Currently available SWE systems have a temporal resolution of about 1/second, making “dynamic”, functional assessments of nerve or muscle possible; we propose two such possible applications: (1) Myotonia describes delayed muscle relaxation in rare hereditary muscle disorders. In six patients with different myotonic muscle disorders and six controls, we performed SWE of the flexor digitorum superficialis muscle in the forearm with a frequency of one measurement per second. From measurements before, during and after brief voluntary contraction, the relaxation time to 10% of normalized shear wave velocity (RT0.1) was determined. 46 imaging sequences were acquired, with a mean RT0.1 of 7.38 s in patients and 1.36 s in control subjects, which is comparable to data obtained by mechanical dynamometry. (2) In carpal tunnel syndrome, reduced nerve mobility mostly in the lateral plane, but also longitudinally, has been described. Wrist and elbow movements, in healthy subjects, are known to alter median nerve tension and, thus, elasticity as detectable by SWE. We present a protocol to investigate whether entrapment at the carpal tunnel affects these posture-induced changes, an effect that might similarly occur in other compressive or traumatic neuropathies. These applications demonstrate how resolving functional manoeuvres by “dynamic” ultrasound SWE may be utilized for clinical diagnostic assessments.

Development of a Robotic Shear Wave Elastography System for Noninvasive Staging of Liver Disease in Murine Models.

Shear wave elastography (SWE) is an ultrasound‐based stiffness quantification technology that is used for noninvasive liver fibrosis assessment. However, despite widescale clinical adoption, SWE is largely unused by preclinical researchers and drug developers for studies of liver disease progression in small animal models due to significant experimental, technical, and reproducibility challenges. Therefore, the aim of this work was to develop a tool designed specifically for assessing liver stiffness and echogenicity in small animals to better enable longitudinal preclinical studies. A high‐frequency linear array transducer (12‐24 MHz) was integrated into a robotic small animal ultrasound system (Vega; SonoVol, Inc., Durham, NC) to perform liver stiffness and echogenicity measurements in three dimensions. The instrument was validated with tissue‐mimicking phantoms and a mouse model of nonalcoholic steatohepatitis. Female C57BL/6J mice (n = 40) were placed on choline‐deficient, L‐amino acid‐defined, high‐fat diet and imaged longitudinally for 15 weeks. A subset was sacrificed after each imaging timepoint (n = 5) for histological validation, and analyses of receiver operating characteristic (ROC) curves were performed. Results demonstrated that robotic measurements of echogenicity and stiffness were most strongly correlated with macrovesicular steatosis (R2 = 0.891) and fibrosis (R2 = 0.839), respectively. For diagnostic classification of fibrosis (Ishak score), areas under ROC (AUROCs) curves were 0.969 for ≥Ishak1, 0.984 for ≥Ishak2, 0.980 for ≥Ishak3, and 0.969 for ≥Ishak4. For classification of macrovesicular steatosis (S‐score), AUROCs were 1.00 for ≥S2 and 0.997 for ≥S3. Average scanning and analysis time was <5 minutes/liver. Conclusion: Robotic SWE in small animals is feasible and sensitive to small changes in liver disease state, facilitating in vivo staging of rodent liver disease with minimal sonographic expertise.

Shear wave speed measurement bias in a viscoelastic phantom across six ultrasound elastography systems: a comparative study with transient elastography and magnetic resonance elastography

PurposeTo quantify the bias of shear wave speed (SWS) measurements in a viscoelastic phantom across six different ultrasound (US) systems and to compare the SWS with those from transient elastography (TE) and magnetic resonance elastography (MRE).MethodsA viscoelastic phantom of stiffness representing fibrotic liver or healthy thyroid was measured with nine (linear probe) and 10 (convex probe) modes of six different US-based shear wave elastography (SWE) systems using linear and convex probes. SWS measurements of three regions of interest were repeated thrice at two focal depths, coupling the probe to the phantom using a jig. An MRE system using three motion-encoding gradient frequencies of 60, 90, and 120 Hz and TE were also used to measure the stiffness of the phantom.ResultsThe SWS from different SWE systems had mean coefficients of variation of 9.0–9.2% and 5.4–5.6% with linear and convex probes, respectively, in viscoelastic phantom measurement. The focal depth was a less significant source of SWS variability than the system. The total average SWS obtained with US-SWE systems was 19.9% higher than that obtained with MRE at 60 Hz, which is commonly used in clinical practice, and 31.5% higher than that obtained with TE using the M probe.ConclusionsDespite the measurement biases associated with the SWE systems, biases were not necessarily consistent, and they changed with the probes used and depth measured. The SWS of the viscoelastic phantom obtained using different modalities increased according to the shear wave frequency used.

Comparison of 2 shear wave elastography systems in reproducibility and accuracy using an elasticity phantom

This study aimed to compare the accuracy and inter- and intra-observer reproducibility of the measured elasticity between 2 shear wave elastography systems. Three breast radiologists examined 8 targets of 4 different levels of stiffness (size: 11 mm, 4 mm) in an elasticity phantom (Customized 049A Elasticity QA Phantom, CIRS, Norfolk, VA, USA) using 2 different shear wave ultrasound elastography systems: SuperSonic Imagine (SSI) (SSI, Aix en Provence, France) and ShearScan (RS-80A, Samsung Medison, Seoul, Korea). Three radiologists performed ultrasound (US) elastography examinations for the phantom lesions using 2 equipment over a 1-week interval. Intra- and inter-observer reproducibility and the accuracy of the measured elasticity were analyzed and compared between the 2 systems. The accuracy of shape was also analyzed by shape-matching between B-mode and elastography color image. Intra-class correlation coefficients (ICC) were used in statistical analysis. For measured elasticity, the intra-observer and inter-observer reproducibility were excellent in both SSI and ShearScan (0.994 and 0.998). The overall accuracy was excellent in both systems, but the accuracy in small lesions (4 mm target) was lower in SSI than ShearScan (0.780 vs 0.967). The accuracy of shape-matching on the elastography image was 59.0% and 81.4% in the SSI and ShearScan, respectively. In conclusion, the SSI and ShearScan showed excellent intra- and inter-observer reproducibility. The accuracy of the Young's modulus was high in both the SSI and ShearScan, but the SSI showed decreased accuracy in measurement of elasticity in small targets and poor shape-matching between the B-mode image and color-coded elastography image.

Non-invasive splenic parameters of portal hypertension: Assessment and utility

BACKGROUNDPortal hypertension is a major complication of cirrhosis that is associated with significant morbidity and mortality. The present gold-standard method to risk stratify and observe cirrhosis patients with portal hypertension is hepatic venous pressure gradient measurement or esophagogastroduodenoscopy. However, these methods are invasive, carry a risk of complications and are associated with significant patient discomfort. Therefore, non-invasive splenic parameters are of clinical interest as potential useful markers in determining the presence of portal hypertension. However, diagnostic accuracy and reproducibility remains unvalidated.AIMTo assess the diagnostic accuracy of spleen stiffness, area and diameter in predicting the presence of portal hypertension.METHODSOf 50 patients with varying liver disease pathologies were prospectively recruited from the St. Mary’s Hospital Liver Unit in London; 25 with evidence of portal hypertension and 25 with no evidence of portal hypertension. Liver stiffness, spleen stiffness, spleen diameter and spleen area were measured using the Philips Affiniti 70 elastography point quantification point shear wave elastography system. The aspartate aminotransferase-to-platelet-ratio-index (APRI) score was also calculated. Performance measures, univariate and multivariate logistic regression were used to evaluate demographic, clinical and elastography variables. Interclass correlation coefficient was used to determine the reproducibility of splenic area and diameter.RESULTSOn univariate and individual performance, platelet count [area under the receiver operating characteristic (AUROC) 0.846, P value < 0.001], spleen area (AUROC 0.828, P value = 0.002) and APRI score (AUROC 0.827, P value < 0.001) were the most accurate variables in identifying the presence of portal hypertension. On multivariate logistic regression models constructed, the combination of spleen area greater than 57.90 cm2 and platelet count less than 126 × 109 had 63.2% sensitivity and 100% specificity, 100% positive predictive value and 100% negative predictive value. An alternative combination of spleen stiffness greater than 29.99 kPa and platelet count less than 126 × 109 had 88% sensitivity, 75% specificity, 78.6% positive predictive value and 85.7% negative predictive value. An interclass correlation coefficient value of 0.98 (95%CI: 0.94-0.99, P value < 0.001) and 0.96 (95%CI: 0.91-0.99, P value < 0.001) were determined for inter-operator variability for spleen area and diameter respectively.CONCLUSIONSpleen area, spleen stiffness and platelet count may be useful markers to assess the presence of portal hypertension in patients of various etiologies.

Three-dimensional shear wave elastography on conventional ultrasound scanners with external vibration

Two-dimensional (2D) ultrasound shear wave elastography (SWE) has been widely used for soft tissue properties assessment. Given that shear waves propagate in three dimensions (3D), extending SWE from 2D to 3D is important for comprehensive and accurate stiffness measurement. However, implementation of 3D SWE on a conventional ultrasound scanner is challenging due to the low volume rate (tens of Hertz) associated with limited parallel receive capability of the scanner’s hardware beamformer. Therefore, we developed an external mechanical vibration-based 3D SWE technique allowing robust 3D shear wave tracking and speed reconstruction for conventional scanners. The aliased shear wave signal detected with a sub-Nyquist sampling frequency was corrected by leveraging the cyclic nature of the sinusoidal shear wave generated by the external vibrator. Shear wave signals from different sub-volumes were aligned in temporal direction to correct time delays from sequential pulse-echo events, followed by 3D speed reconstruction using a 3D local frequency estimation algorithm. The technique was validated on liver fibrosis phantoms with different stiffness, showing good correlation (r = 0.99, p < 0.001) with values measured from a state-of-the-art SWE system (GE LOGIQ E9). The phantoms with different stiffnesses can be well-differentiated regardless of the external vibrator position, indicating the feasibility of the 3D SWE with regard to different shear wave propagation scenarios. Finally, shear wave speed calculated by the 3D method correlated well with magnetic resonance elastography performed on human liver (r = 0.93, p = 0.02), demonstrating the in vivo feasibility. The proposed technique relies on low volume rate imaging and can be implemented on the widely available clinical ultrasound scanners, facilitating its clinical translation to improve liver fibrosis evaluation.

Identifying predictors of upper extremity muscle elasticity with healthy aging

Ultrasound shear wave elastography (SWE) can provide accurate in vivo measurements of the effect of advanced age on muscle elasticity. Our objective was to determine whether passive muscle elasticity was influenced by posture, chronological age, sex, body mass index, and clinical measures of upper extremity function for healthy adults. The dominant arm of 33 male and 33 female participants (ranging from 20 to 89 years old) was examined using a Supersonic Imagine Aixplorer ultrasound SWE system. The mean and standard deviation of shear wave velocity (SWV) was measured from elastography maps for five upper extremity muscles examined at rest: anterior deltoid (AD), biceps brachii (BB), clavicular (CL) and sternocostal (SC) region of the pectoralis major and middle trapezius (MT). Linear mixed models for each muscle were used to assess how SWV was influenced by humeral elevation, chronological age, sex, BMI and three functional measures. All significances are reported at α = 0.05. Humeral elevation influenced shear wave velocity at a statistically significant level for AD, BB, SC and MT (all p < 0.047). Chronological age was a significant predictor of mean SWV for the sternocostal region of the pectoralis major and the middle trapezius (both p < 0.03). These same muscles were also less homogenous (based on their standard deviations) with increased age, particularly for female participants. Performance-based functional assessments of the upper extremity were predictors of mean SWV for the clavicular region of the pectoralis major (all p < 0.04). These results suggest ultrasound SWE has potential utility for assessing age-related changes to muscle elasticity, but these associations were muscle-dependent.

Repeatability and Agreement of Shear Wave Speed Measurements in Phantoms and Human Livers Across 6 Ultrasound 2-Dimensional Shear Wave Elastography Systems.

Ultrasound shear wave elastography (SWE) is an imaging technique that quantifies liver stiffness. However, comparison data across newest ultrasound systems are sparse. The purpose of this study was to assess repeatability and agreement of shear wave speeds (SWSs) across 6 ultrasound 2-dimensional (2D) SWE systems. This cross-sectional, Health Insurance Portability and Accountability Act-compliant study received institutional review board approval. Written informed consent was obtained. Serial 2D SWE examinations were performed with 6 ultrasound systems (Aplio i800, Canon Medical Systems; LOGIQ E10, GE Healthcare; Resona 7, Mindray North America; EPIQ Elite, Philips Healthcare; ACUSON Sequoia, Siemens Medical Solutions; and Aixplorer MACH 30, SuperSonic Imagine) on 4 elastic phantoms (SWS range, 0.82-3.51 m/s) and on livers of 24 adults (healthy volunteers and patients with known liver stiffening). Participants were imaged 2 times per ultrasound system, with 90 to 120 minutes between examinations. Median SWS was calculated from separately acquired SWS measurements per examination (40 phantom measurements and 10 liver measurements per examination). Overall intraclass correlation coefficient (ICC) for intersystem agreement of median SWS across systems was 0.99 (95% confidence interval, 0.96-1.0) in phantoms and 0.66 to 0.69 (95% confidence interval, 0.47-0.84) in humans across systems. Means of median SWS measurements in humans ranged from 1.24 to 1.56 m/s. Average individual subject-level variance (interquartile range/median SWS) across all examinations was 0.07, with an average coefficient of variation of 6.0%. Pairwise ICCs for intersystem agreement in subjects across systems ranged from 0.41 to 0.91; test-retest repeatability in subjects was excellent for all systems, with ICCs ranging from 0.87 to 0.97. There is good to excellent intersystem agreement of measured SWS in elastic phantoms and in vivo livers across 6 ultrasound 2D SWE systems. Test-retest repeatability was excellent for all systems.

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

ObjectiveTo determine inter- and intra-reader reproducibility of shear wave elastography measurements for musculoskeletal soft tissue masses.Materials and methodsIn 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.ResultsOf 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.ConclusionThis 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.

The differential diagnosis of benign and malignant in mass type breast diseases based on the real-time monitoring of full-angle ultrasonic shear wave elastography

Objective To explore the value of full-angle ultrasonic shear wave elastography in differentiating benign and malignant breast diseases. Methods After constructing a new ultrasonic shear wave elastography system, the clinical and ultrasonographic data of 74 patients with mass breast diseases were retrospectively analyzed. The patients were divided into benign group and malignant group according to the pathologic results. Meanwhile, the significant indicators of difference were screened out for ROC analysis, and the curve characteristics were compared. Results Eratio-45°, Eratio-225°, Emax-90°, Emax-270°, Emean-0° and Emean-180° were significantly different between the benign and malignant groups. The AUC of ROC were 0.71, 0.81, 0.83, 0.80, 0.86 and 0.83, respectively. The results of model evaluation showed that the specificity of model-Eratio-45° was relatively low (0.42), while the other 5 indicators showed high specificity (0.73-0.78). Conclusions The full-angle ultrasonic shear wave elastography can provide more information for differentiating benign from malignant breast diseases. Key words: Ultrasonography; Breast neoplasms; Shear wave elastography; Differential diagnosis

Pulmonary Capillary Hemorrhage Induced by Super Sonic Shear Wave Elastography in Rats

The occurrence of the pulmonary capillary hemorrhage (PCH) bioeffect of diagnostic ultrasound in rats was investigated for a SuperSonic Imagine shear wave elastography system (Aixplorer, Supersonic Imagine, Aix-en-Provence, France). The elastography imaging repeated at 1 Hz and consisted of widely spaced B-mode image pulses, supersonic push (SSP) pulses and shear wave imaging (SWI) pulses. Groups of rats anesthetized with ketamine and xylazine, or with ketamine only, were imaged on their right side in a warm water bath for one frame, 30 s and 300 s. The image focus and region of interest were adjusted to give exposure only with the background B-mode imaging, or primarily with the SSP and SWI pulses. A sham group had only low power aiming scans. The lungs were removed 5 min after exposure and evaluated for PCH area and volume. The B mode was notably ineffective and produced significant PCH only at the maximum 0 dB output. The SSP pulses together with the SWI pulses produced significant PCH for 300 s, 30 s and even single image exposures. Peak rarefactional pressure amplitude PCH thresholds for 300 s exposure were the same with or without the B-mode pulses at 1.5 MPa (in situ mechanical index, MIIS = 0.67). A 30 s duration resulted in a slightly increased threshold of 1.7 MPa (MIIS = 0.76). The omission of xylazine from the anesthetic, which reduces the sensitivity of rat lung to PCH occurrence, resulted in an increased threshold of 2.1 MPa (MIIS = 0.94). The unique SSP pulses were much more effective than the B mode, but thresholds were comparable to previous results with other diagnostic ultrasound modes on other systems.

Developing and using fast shear wave elastography to quantify physiologically-relevant tendon forces

Direct quantification of physiologically-relevant tendon forces can be used in a wide range of clinical applications. However, tendon forces have usually been estimated either indirectly by computational models or invasively using force transducers, and direct non-invasive measurement of forces remains a big challenge. The aim of this study was to investigate the feasibility of using Shear Wave Elastography (SWE) for quantifying human tendon forces at physiological levels. An experimental protocol was developed to measure Shear Wave Speed (SWS) and tensile force in a human patellar tendon using SWE and conventional tensile testing to quantify the correlation between SWS and load. The SWE system was customised to allow imaging of fast shear waves expected in human tendons under physiological loading which is outside the normal range of the existing SWE systems. SWS increased from 10.8 m/s to 36.1 m/s with the increasing tensile load from 8 N to 935 N and a strong linear correlation between SWS and load (r = 0.99, p < 0.01) was observed. The findings in this study suggest that SWE can be used as a potential non-invasive method for direct quantification of physiologically-relevant tendon forces, as well as for validating the estimated forces from other methods such as computational models.

Inter-platform reproducibility of liver stiffness measured with two different point shear wave elastography techniques and 2-dimensional shear wave elastography using the comb-push technique.

PurposeThe purpose of this study was to compare the technical success rate and reliability of measurements made using three shear wave elastography (SWE) techniques and to assess the inter-platform reproducibility of the resultant liver stiffness measurements.MethodsThis prospective study included 54 patients with liver disease. Liver stiffness (LS) measurements were obtained using 2-point SWE techniques (Virtual Touch Quantification and S-Shearwave) and 2-dimensional (2D) SWE, with transient elastography (TE) serving as the reference standard. The technical success rates and measurement reliability of the three techniques were compared. LS values measured using the three SWE techniques and TE were compared using Spearman correlation coefficients and 95% Bland-Altman limits of agreement. Intra-class correlation coefficients (ICC) were used to analyze the inter-platform reproducibility of LS measurements.ResultsThe three SWE techniques and TE showed similar technical success rates (P=0.682) but demonstrated significant differences in the reliability of LS measurements (P=0.006) and mean LS measurements (P<0.001). Despite strong correlations (r=0.73-0.94) between SWE systems, various degrees of inter-platform reproducibility (ICC, 0.58-0.92) were observed for the three SWE techniques. The best agreement was observed between S-Shearwave and TE (ICC, 0.92), and the worst agreement was observed between 2D-SWE and TE (ICC, 0.58). In the Bland-Altman analysis, a tendency toward lower LS values with the three SWE techniques than with TE in patients with F3 and F4 disease was observed.ConclusionSignificant inter-system variability was observed in LS measurements made using the three SWE techniques. Therefore, LS values measured using different SWE techniques should not be used interchangeably for longitudinal follow-up.

Reproducibility of liver stiffness measurements made with two different 2-dimensional shear wave elastography systems using the comb-push technique

PurposeThe purpose of this study was to retrospectively compare the technical success and reliability of the measurements made using two 2-dimensional (2D) shear wave elastography (SWE) systems using the comb-push technique from the same manufacturer and to assess the intersystem reproducibility of the resultant liver stiffness (LS) measurements.MethodsNinety-four patients with suspected chronic liver diseases were included in this retrospective study. LS measurements were obtained using two 2D-SWE systems (LOGIQ E9 and LOGIQ S8) from the same manufacturer, with transient elastography (TE) serving as the reference standard, on the same day. The technical success rates and reliability of the measurements of the two 2D-SWE systems were compared. LS values measured using the two 2D-SWE systems and TE were correlated using Spearman correlation coefficients and 95% Bland-Altman limits of agreement. Thereafter, Bland-Altman limits of agreement and intraclass correlation coefficients (ICCs) were used to analyze the intersystem reproducibility of LS measurements.ResultsThe two 2D-SWE systems showed similar technical success rates (98.9% for both) and reliability of LS measurements (92.3% for the LOGIQ E9, 91.2% for the LOGIQ S8; P=0.185). Despite the excellent correlation (ICC=0.92), the mean LS measurements obtained by the two 2D-SWE systems were significantly different (LOGIQ E9, 6.57±2.33 kPa; LOGIQ S8, 6.90±6.64 kPa; P=0.018).ConclusionSignificant intersystem variability was observed in the LS measurements made using the two 2D-SWE systems. Therefore, even 2D-SWE systems from the same manufacturer should not be used interchangeably in longitudinal follow-up.

Shear Wave Elasticity Measurements of Three-Dimensional Cancer Cell Cultures Using Laser Speckle Contrast Imaging

Shear wave elastography (SWE) has been widely adopted for clinical in vivo imaging of tissue elasticity for disease diagnosis, and this modality can be a valuable tool for in vitro mechanobiology studies but its full potential has yet to be explored. Here we present a laser speckle contrast SWE system for noncontact monitoring the spatiotemporal changes of the extracellular matrix (ECM) stiffness in three-dimensional cancer cell culture system while providing submillimeter spatial resolution and temporal resolution of 10 s. The shear modulus measured was found to be strongly correlated with the ECM fiber density in two types of cell culture system (r = 0.832 with P < 0.001, and r = 0.642 with P = 0.024 for cell culture systems containing 4 mg/ml Matrigel with 1 mg/ml and 2 mg/ml collagen type I hydrogel, respectively). Cell migration along the stiffness gradient in the cell culture system and an association between cell proliferation and the local ECM stiffness was observed. As the elasticity measurement is performed without the need of exogenous probes, the proposed method can be used to study how the microenvironmental stiffness interacts with cancer cell behaviors without possible adverse effects of the exogenous particles, and could potentially be an effective screening tool when developing new treatment strategies.

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

The reliability and agreement between shear wave elastography (SWE) systems using different acquisition methodsin muscles is not yet established. The objectives were to determine the reliability of a new SWE system on normal restingmuscles using different acquisition methods and to compare its performance to an established state-of-the-art system. Small, medium and large ROI sizes in addition to longitudinal, oblique and transverse orientations overfive different locations within the rectus femoris muscle were tested using the new system. Results were compared to theestablished system to test for inter-system reproducibility. Lowest within-subject coefficient of variance (4.3%) andshear wave velocity (1.83 m/s) were associated with the medium ROI and longitudinal orientation from the lateral location.This combination resulted in a strong internal agreement of intra-class correlation of 0.76 (0.57-0.89) for the new system andan almost perfect agreement of 0.92 (0.82-0.97) for the established. Inter-system reproducibility for the best combinationwas 0.71 (0.48-1) with a mean velocity difference ±95% limits of agreement of 0.07±0.49 m/s. Altering SWEacquisition methods can produce variable results. The new system produced reliable results that are comparable with but notas reliable as the established.

Intra- and inter-observer variation and accuracy using different shear wave elastography methods to assess circumscribed objects - a phantom study.

The elastic properties of circumscribed tissues (e.g., tendons, lymph nodes, prostates, brain tumors) are of considerableclinical interest. The purpose of this study was thus to compare the Intra-/Inter-observer variation and accuracy in vitro ofpoint shear wave elastography (pSWE) with that of 2D-SWE and to assess 2D-SWE's precision with variable ROI (vROI) incircumscribed objects. Round targets (Elasticity QA Phantom Model 049) were examined for varyingdegrees of stiffness (8, 14, 45, and 80 kPa) and diameters (20/10 mm). Three ultrasound systems and four probes were applied(pSWE: Acuson/S3000 9L4/4C1 and Epiq7 C51, 2D-SWE: Aplio/500 PVT375BT). Three different ROIs were used, namelyfixed ROI (fROI) and variable ROI: rectangular-best-fitted ROI, and round-best-fitted ROI. Each measurement was performedtwice by four observers. A total of 3,604 measurements were conducted. The intra-observer variation of 2D-SWEmeasurements indicated better agreement (Intraclass Correlation Coefficient (ICC) = 0.971; 95% CI=[0.945; 0.985]), thanfor the pSWE measurements (ICC = 0.872; 95% CI=[0.794; 0.92]). With both methods, the shear wave elastography appliedshowed low inter-observer variation: ICC = 0.980; 95% CI=[0.970; 0.987]. However, a significant difference was observedbetween fROI (pSWE) and vROI (2D-SWE) on circumscribed objects in terms of accuracy. The lowest degree of observationerror was detected in situations where the ROI was not "best fitted", but placed within the target of 3mm from the border(target diameter: 20mm; mean relative error = 0.15). When estimating the elastic properties of circumscribedtissues, the different measurement techniques performed by commercial shear wave elastography systems reveal a strong susceptibilityfor observational errors, depending upon the fixed vs. variable ROI of the pSWE vs. 2D-SWE technique.

Validation of Shear Wave Elastography Cutoff Values on the Supersonic Aixplorer for Practical Clinical Use in Liver Fibrosis Staging

The purpose of this study was to determine the validity of previously established ultrasound shear wave elastography (SWE) cut-off values (≥F2 fibrosis) on an independent cohort of patients with chronic liver disease. In this cross-sectional study, approved by the institutional review board and compliant with the Health Insurance Portability and Accountability Act, 338 patients undergoing liver biopsy underwent SWE using an Aixplorer ultrasound machine (SuperSonic Imagine, Aix-en-Provence, France). Median SWE values were calculated from sets of 10 elastograms. A single blinded pathologist evaluated METAVIR fibrosis staging as the gold standard. The study analyzed 277 patients with a mean age of 48 y. On pathologic examination, 212 patients (76.5%) had F0–F1 fibrosis, whereas 65 (23.5%) had ≥F2 fibrosis. Spearman's correlation of fibrosis with SWE was 0.456 (p < 0.001). A cut-off value of 7.29 kPa yielded sensitivity of 95.4% and specificity of 50.5% for the diagnosis of METAVIR stage ≥F2 liver fibrosis in patients with liver disease using the SuperSonic Imagine Aixplorer SWE system.