Ultrasound-based steatosis grading system using 2D-attenuation imaging: An individual patient data meta-analysis with external validation.

BACKGROUND AND AIMS: Noninvasive tools assessing steatosis, such as ultrasonography-based 2D-attenuation imaging (ATI), are needed to tackle the worldwide burden of steatotic liver disease. This one-stage individual patient data (IPD) meta-analysis aimed to create an ATI-based steatosis grading system. APPROACH AND RESULTS: A systematic review (EMBASE + MEDLINE, 2018-2022) identified studies, including patients with histologically or magnetic resonance imaging proton-density fat fraction (MRI-PDFF)-verified ATI for grading steatosis (S0 to S3). One-stage IPD meta-analyses were conducted using generalized mixed models with a random study-specific intercept. Created ATI-based steatosis grading system (aS0 to aS3) was externally validated on a prospective cohort of patients with type 2 diabetes and metabolic dysfunction-associated steatotic liver disease (n=174, histologically and MRI-PDFF-verified steatosis). Eleven enrolled studies included 1374 patients, classified into S0, S1, S2, and S3 in 45.4%, 35.0%, 9.3%, and 10.3% of the cases. ATI was correlated with histological steatosis ( r = 0.60; 95% CI: 0.52, 0.67; p < 0.001) and MRI-PDFF ( r = 0.70; 95% CI: 0.66, 0.73; p < 0.001) but not with liver stiffness ( r = 0.03; 95% CI: -0.04, 0.11, p = 0.343). Steatosis grade was an independent factor associated with ATI (coefficient: 0.24; 95% CI: [0.22, 0.26]; p < 0.001). ATI marginal means within S0, S1, S2, and S3 subpopulations were 0.59 (95% CI: [0.58, 0.61]), 0.69 (95% CI [0.67, 0.71]), 0.78 (95% CI: [0.76, 0.81]), and 0.85 (95% CI: [0.83, 0.88]) dB/cm/MHz; all contrasts between grades were significant ( p < 0.0001). Three ATI thresholds were calibrated to create a new ATI-based steatosis grading system (aS0 to aS3, cutoffs: 0.66, 0.73, and 0.81 dB/cm/MHz). Its external validation showed Obuchowski measures of 0.84 ± 0.02 and 0.82 ± 0.02 with histologically based and MRI-PDFF-based references. CONCLUSIONS: ATI is a reliable, noninvasive marker of steatosis. This validated ATI-based steatosis grading system could be valuable in assessing patients with metabolic dysfunction-associated steatotic liver disease.

US Markers and Necroinflammation, Steatosis, and Fibrosis in Metabolic Dysfunction-associated Steatotic Liver Disease: The iLEAD Study.

Background Attenuation coefficient (AC) and shear-wave speed (SWS) are established US markers for assessing patients with metabolic dysfunction-associated steatotic liver disease (MASLD), while shear-wave dispersion slope (DS) is not. Purpose To assess the relationship between the multiparametric US imaging markers DS, AC, and SWS and liver histopathologic necroinflammation in patients with MASLD. Materials and Methods This international multicenter prospective study enrolled consecutive patients with biopsy-proven MASLD between June 2019 and March 2023. Before biopsy, all participants underwent multiparametric US, and measurements of DS, AC, and SWS were obtained. Multivariable linear regression analyses were performed to assess the association of clinical variables and imaging markers with pathologic findings. The diagnostic performance of imaging markers for determining inflammation grade, steatosis grade, and fibrosis stage was assessed using the area under the receiver operating characteristic curve (AUC). Results A total of 124 participants (mean age, 53 years ± 15 [SD]; 62 males) were evaluated. In multivariable regression, lobular inflammation was associated with DS (regression coefficient, 0.06; P = .02), alanine aminotransferase level (regression coefficient, 0.002; P = .002), and Hispanic or Latino ethnicity (regression coefficient, -0.68; P = .047), while steatosis was associated with AC (regression coefficient, 3.66; P < .001) and fibrosis was associated with SWS (regression coefficient, 2.02; P < .001) and body mass index (regression coefficient, 0.05; P = .02). DS achieved an AUC of 0.72 (95% CI: 0.63, 0.82) for identifying participants with inflammation grade A2 or higher (moderate to severe inflammation). AC showed excellent performance for identifying participants with grade S1 (mild) or higher steatosis (AUC, 0.92 [95% CI: 0.87, 0.97]), while SWS showed excellent performance for identifying participants with fibrosis stage F2 or higher (clinically significant fibrosis) (AUC, 0.91 [95% CI: 0.86, 0.96]). Of the three US markers, SWS showed the highest AUC (0.81 [95% CI: 0.74, 0.89]) for the diagnosis of metabolic dysfunction-associated steatohepatitis. Conclusion Of the three US imaging markers (DS, AC, and SWS), DS was most associated with lobular inflammation grade at histologic examination and demonstrated fair diagnostic performance in distinguishing moderate to severe lobular inflammation. ClinicalTrials.gov Identifier: NCT04012242 Published under a CC BY 4.0 license. Supplemental material is available for this article. See also the editorial by Yin in this issue.

MR and Ultrasound Elastography for Fibrosis Assessment in Children: Practical Implementation and Supporting Evidence-AJR Expert Panel Narrative Review.

Quantitative MRI and ultrasound biomarkers of liver fibrosis have become important tools in the diagnosis and clinical management of children with chronic liver disease (CLD). In particular, MR elastography (MRE) is now routinely performed in clinical practice to evaluate the liver for fibrosis. Ultrasound shear-wave elastography has also become widely performed for this purpose, especially in young children. These noninvasive methods are increasingly used to replace liver biopsy for the diagnosis, quantitative staging, and treatment monitoring of patients with CLD. Although ultrasound has advantages of portability and lower equipment cost, available evidence indicates that MRI may have greater reliability and accuracy in liver fibrosis evaluation. In this AJR Expert Panel Narrative Review, we describe how, why, and when to use MRI- and ultrasound-based elastography methods for liver fibrosis assessment in children. Practical approaches are discussed for adapting and optimizing these methods in children, with consideration of clinical indications, patient preparation, equipment requirements, acquisition technique, as well as pitfalls and confounding factors. Guidance is provided for interpretation and reporting, and representative case examples are presented.

Does Meal or Water Intake Affect Ultrasound Attenuation Coefficient Estimate?

OBJECTIVES: To assess whether meal or water intake may affect the measurement of the ultrasound (US) attenuation coefficient (AC) imaging, a parameter that is directly related to liver fat content. METHODS: The study was performed in two centers (Italy and USA). AC was obtained using the ATI algorithm implemented in the Aplio i-series US systems (Canon Medical Systems, Japan) by one operator at each center. Measurements were performed at baseline and 5, 15, 30, 45 minutes after drinking 500 mL of water (group 1), or 30, 45, 60, 90, 120 minutes after eating a meal of about 600 kcal (group 2). Multilevel generalized estimating equations for repeated measures were used for the statistical analysis to consider the clustered nature of the data. RESULTS: Twenty-six individuals were enrolled: 11 (10 females; age, 43.7 ± 12.5 years) in Italy and 15 (10 females; age, 60.7 ± 6.3 years) in USA. At B-mode US, 10 (38.5%) had liver steatosis. The baseline AC values, in decibel/centimeter/megahertz, were 0.64 (0.12) in group 1 and 0.66 (0.13) in group 2. There was not any significant difference in AC values at every time-point after water or meal intake either in group 1 or group 2. This result did not change including sex, age, and skin-to-liver capsule into the models. CONCLUSIONS: The measurement of the AC, which is a biomarker of liver steatosis, does not require a fasting state and drinking water does not affect the result.

Understanding confounding factors allows for accurate interpretation of liver stiffness measurements by ElastQ, a novel 2D shear wave elastography technique.

PURPOSE: Liver stiffness measurement (LSM) using vibration-controlled transient elastography (VCTE) or two-dimensional shear wave elastography (2D-SWE) is recommended to assess the risk of liver fibrosis and advanced chronic liver disease. Even though both techniques measure liver stiffness, their numerical results often diverge. Confounders and reliability criteria for 2D-SWE have not been systematically investigated. MATERIALS AND METHODS: We prospectively recruited participants with paired LSM by VCTE and the novel 2D-SWE technique ElastQ (Philips) in three European tertiary centers. The following parameters were recorded: sex, age, body mass index (BMI), etiology, laboratory markers of liver damage and function, as well as cholestasis, LSM by VCTE and controlled attenuation parameter (CAP), interquartile range (IQR)/median for VCTE-LSM and ElastQ-LSM, and the skin-to-liver capsule distance. RESULTS: We included 840 participants: 447 (53.2%) males; median age 57.0 [IQR:19.0] years; median BMI 25.4 [6.0] kg/m2; median VCTE-LSM 7.25 [9.2] kPa; median ElastQ-LSM 6.7 [5.4] kPa. On uni- and multivariable modeling (adjusted for LSM), we found that the discrepancy increased with liver stiffness and markers of disease severity. Skin-to-liver capsule distance and BMI affected VCTE-LSM more compared to ElastQ-LSM and significantly increased the discordance between the two measurements. CONCLUSION: The discrepancy of ElastQ-LSM to VCTE-LSM increases with liver stiffness and disease severity. BMI and skin-to-liver capsule distance increase the discrepancy between VCTE- and ElastQ-LSM but affect ElastQ-LSM less. The quality criterion IQR/median ≤ 30% indicates reliable ElastQ-LSM.

Liver Fibrosis, Fat, and Iron Evaluation with MRI and Fibrosis and Fat Evaluation with US: A Practical Guide for Radiologists.

Quantitative imaging biomarkers of liver disease measured by using MRI and US are emerging as important clinical tools in the management of patients with chronic liver disease (CLD). Because of their high accuracy and noninvasive nature, in many cases, these techniques have replaced liver biopsy for the diagnosis, quantitative staging, and treatment monitoring of patients with CLD. The most commonly evaluated imaging biomarkers are surrogates for liver fibrosis, fat, and iron. MR elastography is now routinely performed to evaluate for liver fibrosis and typically combined with MRI-based liver fat and iron quantification to exclude or grade hepatic steatosis and iron overload, respectively. US elastography is also widely performed to evaluate for liver fibrosis and has the advantage of lower equipment cost and greater availability compared with those of MRI. Emerging US fat quantification methods can be performed along with US elastography. The author group, consisting of members of the Society of Abdominal Radiology (SAR) Liver Fibrosis Disease-Focused Panel (DFP), the SAR Hepatic Iron Overload DFP, and the European Society of Radiology, review the basics of liver fibrosis, fat, and iron quantification with MRI and liver fibrosis and fat quantification with US. The authors cover technical requirements, typical case display, quality control and proper measurement technique and case interpretation guidelines, pitfalls, and confounding factors. The authors aim to provide a practical guide for radiologists interpreting these examinations. © RSNA, 2023 See the invited commentary by Ronot in this issue. Quiz questions for this article are available in the supplemental material.

Liver Fat Quantification With Ultrasound: Depth Dependence of Attenuation Coefficient.

OBJECTIVES: The primary aim was to estimate the influence of various depths on ultrasound attenuation coefficient (AC) of multiple vendors in the liver. The secondary aim was to evaluate the impact of region of interest (ROI) size on AC measurements in a subset of participants. METHODS: This Institutional Review Board (IRB)-approved Health Insurance Portability and Accountability Act (HIPAA)-compliant retrospective study was carried out in two centers using AC-Canon and AC-Philips algorithms and extracting AC-Siemens values from ultrasound-derived fat fraction algorithm. Measurements were performed positioning ROI upper edge (3 cm size) at 2, 3, 4, 5 cm from the liver capsule with AC-Canon and AC-Philips and at 1.5, 2, 3 cm with Siemens algorithm. In a subset of participants, measurements were obtained with 1 and 3 cm ROI size. Univariate and multivariate linear regression models and Lin's concordance correlation coefficient (CCC) were used for statistical analysis as appropriate. RESULTS: Three different cohorts were studied. Sixty-three participants (34 females; mean age: 51 ± 14 years) were studied with AC-Canon, 60 (46 females; mean age: 57 ± 11 years) with AC-Philips, and 50 (25 females; 61 ± 13 years) with AC-Siemens. There was a decrease in AC values per 1 cm increase in depth in all. In multivariable analysis, the coefficient was -0.049 (-0.060; -0.038 P < .001) with AC-Canon, -0.058 (-0.066; -0.049 P < .001) with AC-Philips and -0.081 (-0.112; -0.050 P < .001) with AC-Siemens. AC values with 1 cm ROI were significantly higher than those obtained with 3 cm ROI at all depths (P < .001) but the agreement between AC values obtained with different ROI size was excellent (CCC 0.82 [0.77-0.88]). CONCLUSIONS: There is depth dependence in AC measurement that affects results. A standardized protocol with fixed ROI's depth and size is needed.

Point Shear Wave Elastography by ElastPQ for Fibrosis Screening in Patients with NAFLD: A Prospective, Multicenter Comparison to Vibration-Controlled Elastography.

BACKGROUND: Since nonalcoholic fatty liver disease (NAFLD) has become the leading cause of liver disease in the Western world, clinicians need reliable noninvasive tools for the identification of NAFLD-associated fibrosis. Limited evidence on the performance of the novel shear wave elastography technique Elast-PQ (EPQ) in NAFLD is available. METHOD: In this prospective, European multinational study we assessed the diagnostic accuracy of EPQ using vibration-controlled transient elastography (VCTE) as a reference standard. RESULTS: Among 353 NAFLD patients, 332 (94.1%) fulfilled reliability criteria of VCTE and EPQ (defined by IQR/median ≤0.3; 41.3% female, mean age: 59 [IQR: 16.5], mean BMI: 29.0 (7.1)). 4/353 (1.1%) and 17/353 (4.8%) had unreliable VCTE and EPQ measurements, respectively. VCTE-based NAFLD fibrosis stages were F0/F1: 222(66.9%), F2: 41 (12.3%), F3: 30 (9.1%), F4: 39 (11.7%). We found a strong correlation (Pearson R=0.87; p<0.0001) and concordance (Lin's concordance correlation coefficient =0.792) of EPQ with VCTE. EPQ was able to identify NAFLD-fibrosis risk with the following EPQ cutoffs: ≥6.5 kPa for significant fibrosis (≥F2) (≥1.47 m/s; sensitivity: 78%; specificity: 95%; AUROC: 0.94), ≥6.9 kPa for advanced fibrosis (≥F3) (≥1.52 m/s; sens.: 88%, spec.: 89%; AUROC: 0.949), and ≥10.4 kPa for cirrhosis (F4) (≥1.86 m/s; sens.: 87%; spec.: 94%; AUROC: 0.949). CONCLUSION: The point shear wave elastography technique EPQ shows excellent correlation to and concordance with VCTE. EPQ can reliably exclude NAFLD fibrosis <6.0 kPa (<1.41 m/s) and indicate a high risk of advanced fibrosis ≥10.4 kPa (≥1.86 m/s).

US Attenuation for Liver Fat Quantification: An AIUM-RSNA QIBA Pulse-Echo Quantitative Ultrasound Initiative.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, with an estimated prevalence of up to 30% in the general population and higher in people with type 2 diabetes. The assessment of liver fat content is essential to help identify patients with or who are at risk for NAFLD and to follow their disease over time. The American Institute of Ultrasound in Medicine-RSNA Quantitative Imaging Biomarkers Alliance Pulse-Echo Quantitative Ultrasound Initiative was formed to help develop and standardize acquisition protocols and to better understand confounding factors of US-based fat quantification. The three quantitative US parameters explored by the initiative are attenuation, backscatter coefficient, and speed of sound. The purpose of this review is to present the current state of attenuation imaging for fat quantification and to provide expert opinion on examination performance and interpretation. US attenuation methods that need further study are outlined.

Comparison of liver stiffness measurements by a 2D-shear wave technique and transient elastography: results from a European prospective multi-centre study.

OBJECTIVES: To compare liver stiffness measurement (LSM) provided by Canon 2D-shear wave elastography (2D-SWE) and transient elastography (TE), the latter being the reference method. METHODS: Prospective study conducted in four European centres from 2015 to 2016 including patients with various chronic liver diseases who had LSMs with both 2D-SWE and TE on the same day. Median of 10 valid measurements (in kPa) was used for comparison using paired t test, Pearson correlation, intraclass correlation coefficient (ICC) and Bland-Altman plot. The ability of 2D-SWE to stratify patient according to recognised LSM-TE thresholds was assessed by ROC curve analysis. RESULTS: Six hundred forty patients were scanned, where 593 (92.7%), 572 (89.4%) and 537 (83.9%) had reliable LSMs by TE, 2D-SWE and both combined, respectively. In the latter (n = 537, 310 [57.7%] male, mean 55.3 ± 14.8 years), median LSM-TE and LSM-2D-SWE had a mean of 10.1 ± 9.4 kPa (range 2.4-75) and 9.1 ± 6.1 kPa (range 3.6-55.7) (paired t test: p < 0.001), respectively. These were significantly correlated (Pearson r = 0.932, p < 0.001, ICC 0.850 (0.825-0.872), bias 0.99 ± 4.33 kPa [95% limits of agreement - 9.48 to + 7.49] with proportional error towards higher LSM values). LSM-2D-SWE values significantly increased with TE categories (ANOVA: p < 0.001). AUROCs ranged from 0.935 ± 0.010 (95% CI 0.910-0.954) to 0.973 ± 0.009 (95% CI 0.955-0.985), resulting in correct classification of 390/537 (73%) patients. Three 2D-SWE measurements were sufficient for reliable LSMs. CONCLUSION: LSM using 2D-SWE correlates well with TE. It tends to underestimate higher stages of liver fibrosis but correctly classifies the majority of patients. It may be used in TE-derived algorithms to manage patients. KEY POINTS: • Liver stiffness measurement (LSM) by 2D-shear wave elastography (2D-SWE) and transient elastography (TE) are strongly correlated. • 2D-SWE shows proportionately lower LSM values compared to TE, particularly with the higher LSM range. • Three individual measurements by 2D-SWE are sufficient to assess LSM reliably.

Elastography for Pediatric Chronic Liver Disease: A Review and Expert Opinion.

In adults with chronic liver diseases, ultrasound and magnetic resonance shear wave elastography (SWE) can replace liver biopsy in several clinical scenarios. Several guidelines on the use of ultrasound SWE for the adult population have been published. However, the number of publications in the pediatric population is limited, and available guidelines on SWE do not specifically address pediatric chronic liver diseases. In this article, we review the literature on the use of SWE for pediatric chronic liver diseases and provide expert opinion on how to use SWE, both ultrasound and magnetic resonance techniques, in the pediatric population.

Performance of the Attenuation Imaging Technology in the Detection of Liver Steatosis.

OBJECTIVES: The main aim was to assess the performance and cutoff value for the detection of liver steatosis (grade S > 0) with the Attenuation Imaging-Penetration (ATI-Pen) algorithm available on the Aplio i-series ultrasound systems (Canon Medical Systems, Otawara, Japan). The magnetic resonance imaging-derived proton density fat fraction (MRI-PDFF) was used as the reference standard. Secondary aims were to compare the results to those obtained with the previous ATI algorithm (Attenuation Imaging-General [ATI-Gen]) and with the controlled attenuation parameter (CAP) and to generate a regression equation between ATI-Pen and ATI-Gen values. METHODS: Consecutive adult patients potentially at risk of liver steatosis were prospectively enrolled. Each patient underwent ultrasound quantification of liver steatosis with ATI-Pen and ATI-Gen and a CAP assessment with the FibroScan system (Echosens, Paris, France). The MRI-PDFF evaluation was performed within a week. The correlations between ATI-Pen, ATI-Gen, the CAP, and the MRI-PDFF were analyzed with the Pearson rank correlation coefficient. The diagnostic performance of ATI-Pen, ATI-Gen, and the CAP was assessed with receiver operating characteristic curves and an area under the receiver operating characteristic curve (AUROC) analysis. RESULTS: Seventy-two individuals (31 male and 41 female) were enrolled. Correlation coefficients of ATI-Pen, ATI-Gen, and the CAP with the MRI-PDFF were 0.78, 0.83, and 0.58, respectively. The AUROCs of ATI-Pen, ATI-Gen, and the CAP for detecting steatosis (S > 0) were 0.90 (95% confidence interval, 0.81-0.96), 0.92 (0.82-0.98), and 0.85 (0.74-0.92), and the cutoffs were greater than 0.69 dB/cm/MHz, greater than 0.62 dB/cm/MHz, and greater than 273 dB/m. The regression equation between ATI-Pen and ATI-Gen was ATI-Pen = 0.88 ATI-Gen + 0.13. CONCLUSIONS: Attenuation Imaging is a reliable tool for detecting liver steatosis, showing an excellent correlation with the MRI-PDFF and high performance with AUROCs of 0.90 or higher.

Update to the Society of Radiologists in Ultrasound Liver Elastography Consensus Statement.

This multidisciplinary update of the Society of Radiologists in Ultrasound consensus statement on liver elastography incorporates the large volume of new information available in the literature since the initial publication. The recommended procedure for acquiring stiffness measurements is reviewed. There has been substantial improvement in the acoustic radiation force impulse (ARFI) technology-most notably the addition of a quality assessment of the shear wave propagation. Due to the efforts of the Quantitative Imaging Biomarkers Alliance, or QIBA, the variability of liver stiffness measurements between systems had decreased. There are now effective treatments for hepatitis B and hepatitis C, and follow-up after effective treatment should be based on the use of the delta change of the value obtained at viral eradication or suppression. Because the detection of compensated advanced chronic liver disease (cACLD) is very important, the new guidelines are made based on the probability of cACLD for given stiffness values. The panel recommends a vendor-neutral rule of four for interpretation for ARFI techniques. This new method simplifies interpretation of liver stiffness results and is more clinically relevant.

Assessment of biopsy-proven liver fibrosis by two-dimensional shear wave elastography: An individual patient data-based meta-analysis.

Two-dimensional shear wave elastography (2D-SWE) has proven to be efficient for the evaluation of liver fibrosis in small to moderate-sized clinical trials. We aimed at running a larger-scale meta-analysis of individual data. Centers which have worked with Aixplorer ultrasound equipment were contacted to share their data. Retrospective statistical analysis used direct and paired receiver operating characteristic and area under the receiver operating characteristic curve (AUROC) analyses, accounting for random effects. Data on both 2D-SWE and liver biopsy were available for 1,134 patients from 13 sites, as well as on successful transient elastography in 665 patients. Most patients had chronic hepatitis C (n = 379), hepatitis B (n = 400), or nonalcoholic fatty liver disease (n = 156). AUROCs of 2D-SWE in patients with hepatitis C, hepatitis B, and nonalcoholic fatty liver disease were 86.3%, 90.6%, and 85.5% for diagnosing significant fibrosis and 92.9%, 95.5%, and 91.7% for diagnosing cirrhosis, respectively. The AUROC of 2D-SWE was 0.022-0.084 (95% confidence interval) larger than the AUROC of transient elastography for diagnosing significant fibrosis (P = 0.001) and 0.003-0.034 for diagnosing cirrhosis (P = 0.022) in all patients. This difference was strongest in hepatitis B patients. CONCLUSION: 2D-SWE has good to excellent performance for the noninvasive staging of liver fibrosis in patients with hepatitis B; further prospective studies are needed for head-to-head comparison between 2D-SWE and other imaging modalities to establish disease-specific appropriate cutoff points for assessment of fibrosis stage. (Hepatology 2018;67:260-272).

Review of Liver Elastography Guidelines.

Nowadays, shear wave elastographic techniques have brought a substantial reduction of liver biopsies performed to stage liver fibrosis in patients with chronic hepatitis. The availability of accurate noninvasive methods for the assessment of liver fibrosis was an important breakthrough and prompted ultrasound federations of societies as well as clinical and radiologic societies to issue international guidelines or consensus statements on the clinical applications of shear wave elastographic techniques. This article reviews the guidelines that have been published as of today.

Evaluation of Inter-System Variability in Liver Stiffness Measurements.

AIM: The primary aim of this study was to determine the inter-system variability of liver stiffness measurements (LSMs) in patients with varying degrees of liver stiffness. The secondary aim was to determine the inter-observer variability of measurements. MATERIALS AND METHODS: 21 individuals affected by chronic hepatitis C and 5 healthy individuals were prospectively enrolled. The assessment of LSMs was performed using six ultrasound (US) systems, four of which with point shear wave elastography (p-SWE) and two with 2 D shear wave elastography (2D-SWE) systems. The Fibroscan (Echosens, France) was used as the reference standard. Four observers performed the measurements in pairs (A-B, C-D). The agreement between different observers or methods was calculated using Lin's concordance correlation coefficient. The Bland-Altman limits of agreement (LOA) were calculated as well. RESULTS: There was agreement above 0.80 for all pairs of systems. The mean difference between the values of the systems with 2D-SWE technique was 1.54 kPa, whereas the maximum mean difference between the values of three out of four systems with the pSWE technique was 0.79 kPa. The intra-patient concordance for all systems was 0.89 (95 % CI: 0.83 - 0.94). Inter-observer agreement was 0.96 (95 % CI: 0.94 - 0.98) for the pair of observers A-B and 0.93 (95 % CI: 0.89 - 0.96) for the pair of observers C-D. CONCLUSION: The results of this study show that the agreement between LSMs performed with different US systems is good to excellent and the overall inter-observer agreement in "ideal conditions" is above 0.90 in expert hands.