Comparison of the Reliability of Acoustic Radiation Force Impulse Imaging and Supersonic Shear Imaging in Measurement of Liver Stiffness

Combined model with acoustic radiation force impulse to rule out high-risk varices in HBV-related cirrhosis with viral suppression

AIMS

To prospectively evaluate the performance of spleen stiffness measurement (SSM) and liver stiffness measurement (LSM) via acoustic radiation force impulse (ARFI) imaging combined with platelet counts (PLT) in ruling out HRV in HBV-related cirrhotic patients with viral suppression.

METHODS

Patients with cirrhosis enrolled between June 2020-March 2022 were divided into a derivation cohort and validation cohort. LSM and SSM ARFI-based, and esophagogastroduodenoscopy (EGD) were performed at enrollment.

RESULTS

In the derivation cohort, overall, 236 HBV-related cirrhotic patients with maintained viral suppression were enrolled, and the prevalence of HRV was 19.5% (46/236). With the aim of identifying HRV, the most accurate LSM and SSM cut-offs were chosen of 1.46 m/s and 2.28 m/s, respectively. The combined model (LSM<1.46 m/s and PLT>150 × 109/L strategy combined with SSM ≤ 2.28 m/s) can spare 38.6% of EGDs and 4.3% of HRV cases were misclassified. In the validation cohort, we analysed 323 HBV-related cirrhotic patients with maintained viral suppression and validated the combined model can spare 33.4% (108/323) of EGD, and the HRV missed rate was 3.4%.

CONCLUSIONS

A non-invasive prediction model combining LSM<1.46 m/s and PLT>150 × 109/L strategy with SSM ≤ 2.28 m/s exhibited excellent performance in ruling out HRV and avoided a significantly large number (38.6% vs 33.4%) of unnecessary EGDs in HBV-related cirrhotic patients with viral suppression.

Artifacts in two-dimensional shear wave elastography of liver

BACKGROUND

Artifacts are common when using two-dimensional shear wave elastography (2-D SWE) to measure liver stiffness (LS), but they are poorly recognized.

AIM

To investigate the presence and influence of artifacts in 2-D SWE of liver.

METHODS

We included 158 patients with chronic liver disease, who underwent 2-D SWE examination by a novice and an expert. A cross line at the center of the elastogram was drawn and was divided it into four locations: top-left, top-right, bottom-left, and bottom-right. The occurrence frequency of artifacts in different locations was compared. The influence of artifacts on the LS measurements was evaluated by comparing the elastogram with the most artifacts (EMA) and the elastogram with the least artifacts (ELA).

RESULTS

The percentage of elastograms with artifacts in the novice (51.7%) was significantly higher than that of the expert (19.6%) (P < 0.001). It was found that both operators had the highest frequency of artifacts at bottom-left, followed by top-left and bottom-right, and top-right had the lowest frequency. The LS values (LSVs) and standard deviation values of EMAs were significantly higher than those of ELAs for both operators. An intraclass correlation coefficient value of 0.96 was found in the LSVs of EMAs of the two operators, and it increased to 0.98 when the LSVs of the ELAs were used. Both operators had lower stability index values for EMAs than ELAs, but the difference was only statistically significant for the novice.

CONCLUSION

Artifacts are common when using 2-D SWE to measure LS, especially for the novice. Artifacts may lead to the overestimation of LS and reduce the repeatability and reliability of LS measurements.

Liver and spleen stiffness for the diagnosis of oesophageal varices in adults with chronic liver disease

This is a protocol for a Cochrane Review (diagnostic). The objectives are as follows:

To assess the diagnostic accuracy of liver stiffness and spleen stiffness, separately or in combination, as measured by vibration‐controlled transient elastography (VCTE) in detection of any oesophageal varices in adults with chronic liver disease. We will regard a combination of tests as positive when at least one is positive.

To compare the diagnostic accuracy of individual tests (liver stiffness and spleen stiffness measured by VCTE) directly and versus the combination of both tests (considering positive when at least one is positive) in detecting any oesophageal varices.

To assess the diagnostic accuracy of liver stiffness and spleen stiffness, separately or in combination, as measured by other elastography techniques (2D‐shear wave elastography (2D‐SWE), point shear wave elastography (pSWE), magnetic resonance elastography (MRE)) in detection of any oesophageal varices in adults with chronic liver disease. We will regard a combination of tests as positive when at least one is positive.

To compare the diagnostic accuracy of liver stiffness and spleen stiffness measured by VCTE with other techniques (pSWE, 2D‐SWE, MRE) in detection of any oesophageal varices in adults with chronic liver disease.

Application of the shear wave elastography in the assessment of carotid body tumors: A preliminary study

Objectives

To evaluate the elasticity of carotid body tumors (CBTs) by two-dimensional shear wave elastography (SWE).

Methods

22 pathologically or clinically confirmed CBTs in 16 patients were scanned by SWE. The maximum elasticity value (Emax) and its standard deviation (SDmax) in kPa and m/s for CBTs were obtained by placing a round ROI (2-3 mm) on the stiffest region of the CBTs. Elasticity value was compared between hard and soft groups at manual palpation, benign and malignant groups and among three Shamblin types. The area under the receiver operating characteristic curve (AUC) analysis was performed to evaluate the performance of SWE in the malignancy prediction of CBTs. Sensitivity, specificity and accuracy were calculated. The cut-off value was obtained by using the Youden index.

Results

There were 19 benign CBTs and 3 malignant CBTs. Emax (kPa and m/s) and SDmax (kPa) were significantly higher in the hard group than in the soft group at manual palpation (P<0.05); The distribution of Emax in kPa and m/s and SDmax in kPa were different in the three Shamblin types (P<0.05), Emax (kPa and m/s)increased from shambling I to Shambling II and Shambling III; Emax (kPa and m/s) were significantly higher in the malignant CBTs than in the benign ones (P<0.05). Emax in kPa and m/s had the similar AUC value (AUC=0.947, P=1.0000) for the prediction of malignant CBTs. Emax in kPa with the cut-off 124.9kPa showed a sensitivity of 100.0%, specificity of 94.7%, and an accuracy of 95.5% (Z=8.500, P<0.0001); Emax in m/s with the cut-off 5.9m/s showed a sensitivity of 100.0%, specificity of 89.5% and an accuracy of 90.9% for the prediction of malignant CBTs (Z=9.143, P<0.0001).

Conclusions

Quantitative analysis of SWE obtained the good performance in the elasticity assessment of CBTs.

Sonoelastography: A powerful technique in musculoskeletal imaging

Sonoelastography is a powerful method available to observe the musculoskeletal system, and appears particularly valuable in detecting early tendinopathies, pursuing complaints of localized musculoskeletal pain, analyzing soft tissue masses, and research applications in musculoskeletal medicine.

Intra-individual comparison of twodimensional shear wave elastography techniques using plane wave imaging and the multi-beam technique: are they interchangeable in measuring liver fibrosis?

PURPOSE

This study compared two different two-dimensional shear wave elastography techniques-plane wave imaging (PWI) and multi-beam (MB) imaging-from the same vendor to evaluate liver fibrosis.

METHODS

In this prospective study, 42 patients with chronic liver disease who had recently undergone magnetic resonance elastography (<3 months) were enrolled, and their liver stiffness (LS) values were measured using PWI or MB. The LS values (kPa) were compared using the Wilcoxon rank-sum test. Inter-technique reproducibility and intra-observer repeatability were assessed using Bland-Altman analysis with 95% limits of agreement (LOA) and coefficients of variation (CVs). The cutoff values for predicting severe fibrosis (≥F3) were estimated using receiver operating characteristic curve (ROC) analysis, with magnetic resonance elastography as the reference standard.

RESULTS

PWI exhibited technical failure in four patients. Therefore, 38 patients underwent both examinations. The LS values showed moderate agreement between PWI and MB (CV, 22.5%) and 95% LOA of -3.71 to 7.44 kPa. The MB technique showed good intra-observer agreement (CV, 8.1%), while PWI showed moderate agreement (CV, 11.0%). The cutoff values of PWI and MB for diagnosing ≥F3 were 12.3 kPa and 13.8 kPa, respectively, with areas under the ROC curve of 0.89 and 0.95 (sensitivity, 100% and 100%; specificity, 65.6% and 85.7%).

CONCLUSION

The LS values significantly differed between PWI and MB, hindering their interchangeable use in longitudinal follow-up. Considering its low technical failure rate and better repeatability, the MB technique may be preferable for evaluating liver fibrosis in chronic liver disease patients.

Assessment of clinically significant portal hypertension by two-dimensional shear wave elastography

BACKGROUND AND AIMS

To evaluate two-dimensional shear wave elastography (2DSWE) in parallel with transient elastography (TE) for diagnosing clinically significant portal hypertension (CSPH) and high-risk varices (HRV) in patients with chronic liver disease.

PATIENTS AND METHODS

Consecutive patients with suspicion of compensated advanced chronic liver disease (cACLD) [liver stiffness measurement (LSM) ≥ 10 kPa by TE, or morphological signs suggestive of cACLD on imaging], with no history of liver decompensation, underwent hepatic venous pressure gradient (HVPG) measurement, transjugular liver biopsy and esophagogastroduodenoscopy, which served as the reference methods for diagnosing CSPH, cACLD and HRV. All patients underwent LSM and spleen stiffness measurements (SSM) by 2DSWE and TE.

RESULTS

Seventy-six (76) patients were included (78% men, mean age 62 years, body mass index 28.3 kg/m² , 36.8% alcoholic, 30.3% non-alcoholic fatty liver disease, 14.5% viral hepatitis). Of them, 80.3%, 69.7%, 52.6% and 22.4% had cACLD, cirrhosis, CSPH and HRV respectively. LSM performed better than SSM in diagnosing CSPH and HRV. For CSPH, AUROCs (0.926 vs. 0.866), optimal cut-offs (20.1 vs. 20.2 kPa) and sensitivity/specificity (80.5%/94.3% vs. 77.5% /86.1%) were comparable for 2DSWE and TE. Ruling-out of CSPH by 2DSWE (LSM at cut-off with ≥90% sensitivity (13.5 kPa) and platelets ≥ 150 x 10⁹ /L) performed comparably to TE, with 1/24 cases falsely classified as negative. For HRV, AUROCs were similar (0.875 2DSWE, 0.851 TE) with similar optimal LSM cut-offs enabling 100% sensitivity and ruling-out HRV.

CONCLUSION

Liver stiffness measurement by 2DSWE appears to perform equally well as TE for diagnosing CSPH and ruling-out HRV in compensated chronic liver disease.

Assessment of congestion and clinical outcomes in patients with chronic heart failure using shear wave elasticity

Aims

The relief of congestion is essential for the prevention of worsening heart failure (HF) resulting in hospitalizations. Assessment of the degree of organ congestion in the chronic phase of HF is important for determining therapeutic strategies. The aim of this study was to evaluate the efficacy of shear wave (SW) elasticity for assessing congestion and clinical outcomes in patients with chronic HF.

Methods and results

We prospectively enrolled 345 consecutive patients with chronic HF who underwent SW elastography at outpatient clinic. Patients were divided into two groups according to the median value of SW elasticity: low group (SW elasticity <6.4 kPa, n = 176) and high group (SW elasticity ≥6.4 kPa, n = 169). The endpoint was cardiovascular death or hospitalization for HF. During the median follow‐up period of 19 months (range: 7–36 months), cardiovascular death or hospitalization for HF occurred in 4 patients of low group and 27 patients of high group. In high group, 8 patients died, and 19 patients were hospitalized for HF. In low group, 3 patients died, and 1 patient was hospitalized. Kaplan–Meier analysis showed that the event‐free survival rate was worse in high group than in low group (log‐rank test, P = 0.004). After adjusting for variables, high SW elasticity was independently related to cardiac events. In multivariate regression analysis, SW elasticity was correlated with left atrial volume index, early diastolic mitral inflow velocity to mitral annular velocity ratio, and inferior vena cava diameter.

Conclusions

The SW elasticity reflected haemodynamic congestion in patients with chronic HF, which was related to cardiac events.

A Cross-Machine Comparison of Shear-Wave Speed Measurements Using 2D Shear-Wave Elastography in the Normal Female Breast

Quantitative measures of radiation-induced breast stiffness are required to support clinical studies of novel breast radiotherapy regimens and exploration of personalised therapy, however, variation between shear-wave elastography (SWE) machines may limit the usefulness of shear-wave speed (cs) for this purpose. Mean cs measured in four healthy volunteers’ breasts and a phantom using 2D-SWE machines Acuson S2000 (Siemens Medical Solutions) and Aixplorer (Supersonic Imagine) were compared. Shear-wave speed was measured in the skin region, subcutaneous adipose tissue and parenchyma. cs estimates were on average 2.3% greater when using the Aixplorer compared to S2000 in vitro. In vivo, cs estimates were on average 43.7%, 36.3% and 49.9% significantly greater (p << 0.01) when using the Aixplorer compared to S2000, for skin region, subcutaneous adipose tissue and parenchyma, respectively. In conclusion, despite relatively small differences between machines observed in vitro, large differences in absolute measures of shear wave speed measured were observed in vivo, which may prevent pooling of cross-machine data in clinical studies of the breast.

The role of elastography in viral hepatitis and autoimmune hepatitis

The prognosis of chronic liver diseases, which represent a major public health problem, is mainly linked to the extent and progression of liver fibrosis and the subsequent risk of developing cirrhosis and related complications, mainly hepatocellular carcinoma. During the past decade many noninvasive methods and in particular electrographic techniques, have been developed to reduce the need for liver biopsy in staging fibrosis and to overcome whenever possible its limitations, mainly: invasiveness, costs, low reproducibility and poor acceptance by patients. The aim of this review was to provide a comprehensive review of the role of elastography techniques in viral chronic liver diseases and autoimmune hepatitis, with the focus on the possible advantages and limitations of these techniques and on their diagnostic accuracy in predicting the stage of liver fibrosis.

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.

Elastography for Longitudinal Assessment of Liver Fibrosis after Antiviral Therapy: A Review

Chronic hepatitis B or C viral infection is a common cause of liver cirrhosis and hepatocellular carcinoma. Fibrosis regression can be achieved after long-term antiviral therapy (AVT). Monitoring of dynamic changes in liver fibrosis after treatment is essential for establishing prognosis and formulation of a follow-up surveillance program. Routine surveillance of fibrosis after AVT by liver biopsy, the gold standard for fibrosis assessment, is hindered by its invasive nature, sampling error and observer variability. Elastography is a noninvasive quantitative alternative that has been widely used and validated for the staging of liver fibrosis prior to treatment. Recently, increasing research interest has been focused on the role of elastography in longitudinal assessment of liver fibrosis after AVT. In this review, the basic principles, acquisition techniques, diagnostic performances, and strengths and limitations of ultrasound elastography and magnetic resonance elastography are presented. Emerging evidence regarding the use of elastography techniques for the monitoring of liver fibrosis after AVT is summarized. Current challenges and future directions are also discussed, designed to optimize the application of these techniques in clinical practice.

What does liver elastography measure? Technical aspects and methodology

Elastography can be thought as an extension of the ancient technique of palpation. After giving a short introduction to the history of elastography, the different technologies that are nowadays available and the physics behind them, the article focuses on the assessment of liver stiffness in patients with diffuse liver disease using shear wave elastography (SWE). Practical advices on how to perform the SWE techniques and on the factors that should be considered for a correct interpretation of the results are given. This paper aimed to provide a practical guide for beginners and advanced clinical users to better understand technical aspects, methodologies and terminology.

Organ Stiffness in the Work-Up of Myelofibrosis and Philadelphia-Negative Chronic Myeloproliferative Neoplasms

To define the role of spleen stiffness (SS) and liver stiffness (LS) in myelofibrosis and other Philadelphia (Ph)-negative myeloproliferative neoplasms (MPNs), we studied, by ultrasonography (US) and elastography (ES), 70 consecutive patients with myelofibrosis (MF) (no.43), essential thrombocythemia (ET) (no.10), and polycythemia vera (PV) (no.17). Overall, the median SS was not different between patients with MF and PV (p = 0.9); however, both MF and PV groups had significantly higher SS than the ET group (p = 0.011 and p = 0.035, respectively) and healthy controls (p < 0.0001 and p = 0.002, respectively). In patients with MF, SS values above 40 kPa were significantly associated with worse progression-free survival (PFS) (p = 0.012; HR = 3.2). SS also correlated with the extension of bone marrow fibrosis (BMF) (p < 0.0001). SS was higher in advanced fibrotic stages MF-2, MF-3 (W.H.O. criteria) than in pre-fibrotic/early fibrotic stages (MF-0, MF-1) (p < 0.0001) and PFS was significantly different in the two cohorts, with values of 63% and 85%, respectively (p = 0.038; HR = 2.61). LS significantly differed between the patient cohort with MF and healthy controls (p = 0.001), but not between the patient cohorts with ET and PV and healthy controls (p = 0.999 and p = 0.101, respectively). We can conclude that organ stiffness adds valuable information to the clinical work-up of MPNs and could be employed to define patients at a higher risk of progression.

Applying Non-Invasive Fibrosis Measurements in NAFLD/NASH: Progress to Date

Nonalcoholic fatty liver disease (NAFLD) has now become a worldwide health issue due to the obesity epidemic, affecting approximately 90% of the obese population and 15-40% of the general population. It is the most common form of chronic liver disease in the United States. NAFLD constitutes a spectrum of diseases ranging in severity from mild, such as fatty liver, progressing into nonalcoholic steatohepatitis (NASH), then fibrosis, and ending with cirrhosis. NASH and increasing fibrosis stage are associated with increased morbidity and mortality; the fibrosis stage is therefore a critical element of risk stratification needed to determine therapeutic approach and also the response to treatment. Liver biopsy is considered the 'gold standard' in the diagnosis of NAFLD. However, it is not practical for widespread clinical use because it is invasive, costly, and associated with complications including occasional death. These limitations have driven the development of noninvasive tests that can accurately predict the fibrosis stage in those with NAFLD. In this review, we provide a concise overview of different non-invasive measurements used for NAFLD/NASH.

Validation of a New Point Shear-Wave Elastography Method for Noninvasive Assessment of Liver Fibrosis: A Prospective Multicenter Study

Objective

To validate the diagnostic value of a new point shear-wave elastography method, S-shearwave elastography (S-SWE; Samsung Medison Co., Ltd.), in noninvasive assessment of liver fibrosis.

Materials and Methods

In this prospective multicenter study, liver stiffness (LS) measurements for 600 participants were obtained with both S-SWE and transient elastography (TE). The rates of unsuccessful LS measurements in S-SWE and TE were compared, and correlations between S-SWE and TE measurements were assessed. In 107 patients with histologic reference data, the optimal LS cut-off values for predicting severe fibrosis and cirrhosis on S-SWE were determined using receiver operating characteristic (ROC) curve analysis. The LS cut-off values in S-SWE were then validated in 463 patients without histologic reference data by using TE values as the reference standard, and the sensitivity and specificity of the cut-off values for predicting severe fibrosis and cirrhosis were calculated.

Results

The frequency of unsuccessful LS measurements on TE (4.5%, 27/600) was significantly higher than that (0.7%, 4/600) on S-SWE (p < 0.001). LS measurements on S-SWE showed a significant correlation with TE values (r = 0.880, p < 0.001). In 107 patients with histological reference data, the areas under the ROC curves on S-SWE were 0.845 and 0.850, with optimal cut-offs of 7.0 kilopascals (kPa) and 9.7 kPa, for the diagnosis of severe fibrosis and cirrhosis, respectively. Using these cut-off values, S-SWE showed sensitivities of 92.9% and 97.4% and specificities of 89.5% and 83.1% in TE-based evaluations of severe fibrosis and cirrhosis, respectively.

Conclusion

LS measurements on S-SWE were well correlated with those on TE. In addition, S-SWE provided good diagnostic performance for staging of hepatic fibrosis, with a lower rate of unsuccessful LS measurements compared with TE.

Technical Performance of Two-Dimensional Shear Wave Elastography for Measuring Liver Stiffness: A Systematic Review and Meta-Analysis

Objective

To assess the technical performance of two-dimensional shear wave elastography (2D-SWE) for measuring liver stiffness.

Materials and Methods

The Ovid-MEDLINE and EMBASE databases were searched for studies reporting the technical performance of 2D-SWE, including concerns with technical failures, unreliable measurements, interobserver reliability, and/or intraobserver reliability, published until June 30, 2018. The pooled proportion of technical failure and unreliable measurements was calculated using meta-analytic pooling via the random-effects model and inverse variance method for calculating weights. Subgroup analyses were performed to explore potential causes of heterogeneity. The pooled intraclass correlation coefficients (ICCs) for interobserver and intraobserver reliability were calculated using the Hedges-Olkin method with Fisher's Z transformation of the correlation coefficient.

Results

The search yielded 34 articles. From 20 2D-SWE studies including 6196 patients, the pooled proportion of technical failure was 2.3% (95% confidence interval [CI], 1.3–3.9%). The pooled proportion of unreliable measurements from 20 studies including 6961 patients was 7.5% (95% CI, 4.7–11.7%). In the subgroup analyses, studies conducting more than three measurements showed fewer unreliable measurements than did those with three measurements or less, but no intergroup difference was found in technical failure. The pooled ICCs for interobserver reliability (from 10 studies including 517 patients) and intraobserver reliability (from 7 studies including 679 patients) were 0.87 (95% CI, 0.82–0.90) and 0.93 (95% CI, 0.89–0.95), respectively, suggesting good to excellent reliability.

Conclusion

2D-SWE shows good technical performance for assessing liver stiffness, with high technical success and reliability. Future studies should establish the quality criteria and optimal number of measurements.

Elastography Techniques for the Assessment of Liver Fibrosis in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is expected to increase in prevalence because of the ongoing epidemics of obesity and diabetes, and it has become a major cause of chronic liver disease worldwide. Liver fibrosis is associated with long-term outcomes in patients with NAFLD. Liver biopsy is recommended as the gold standard method for the staging of liver fibrosis. However, it has several problems. Therefore, simple and noninvasive methods for the diagnosis and staging of liver fibrosis are urgently needed in place of biopsy. This review discusses recent studies of elastography techniques (vibration-controlled transient elastography, point shear wave elastography, two-dimensional shear wave elastography, and magnetic resonance elastography) that can be used for the assessment of liver fibrosis in patients with NAFLD.

Comparison of point and 2-dimensional shear wave elastography for the evaluation of liver fibrosis

PURPOSE

This study aimed to assess the technical performance of ElastQ Imaging compared with ElastPQ and to investigate the correlation between liver stiffness (LS) values obtained using these two techniques.

METHODS

This retrospective study included 249 patients who underwent LS measurements using both ElastPQ and ElastQ Imaging equipped on the same machine. The applicability, repeatability (coefficient of variation [CV]), acquisition time, and LS values were compared using the chi-square or Wilcoxon signed-rank tests. In the development group, the correlation between the LS values obtained by the two techniques was assessed with Spearman correlation coefficients and linear regression analysis. In the validation group, the agreement between the estimated and real LS values was evaluated using a Bland-Altman plot.

RESULTS

ElastQ Imaging had higher applicability (94.0% vs. 78.3%, P<0.001) and higher repeatability, with a lower median CV (0.127 vs. 0.164, P<0.001) than did ElastPQ. The median acquisition time of ElastQ Imaging was significantly shorter than that of ElastPQ (45.5 seconds vs. 96.5 seconds, P<0.001). The median LS value obtained using ElastQ Imaging was significantly higher than that obtained using ElastPQ (5.60 kPa vs. 5.23 kPa, P<0.001). The LS values between the two techniques exhibited a strong positive correlation (r=0.851, P<0.001) in the development group. The mean difference and 95% limits of agreement were 0.0 kPa (-3.9 to 3.9 kPa) in the validation group.

CONCLUSION

ElastQ Imaging may be more reliable and faster than ElastPQ, with strongly correlated LS measurements.

Liver stiffness and perfusion changes for hepatic sinusoidal obstruction syndrome in rabbit model

BACKGROUND

Hepatic sinusoidal obstruction syndrome (SOS) is caused by damage to hepatic sinusoidal endothelial cells that results in fibrous obliteration of intrahepatic venules and necrosis of hepatocytes. Currently the diagnosis is primarily based on nonspecific clinical features and invasive liver biopsy. Therefore, noninvasive imaging methods are required for the early diagnosis and severity assessment of hepatic SOS.

AIM

To determine the effectiveness of supersonic shear wave imaging (SSI) and dual energy computed tomography (DECT) for diagnosing hepatic SOS using a rabbit model.

METHODS

Among nine New Zealand white rabbits (3-4 kg, male), three in control group ingested normal saline for 20 d and six in the SOS group ingested 6-thioguanine (5 mg/kg/d) for 20 d. Liver stiffness was measured using SSI on days 0, 3, 10, and 20. On the same days, liver perfusion was evaluated from virtual monochromatic images of 55 keV and iodine map using DECT. Morphologic changes in the liver were assessed using CT. Final pathology scores were compared between the two groups. Liver stiffness and perfusion parameters were compared according to the groups, days, and pathology scores.

RESULTS

Final pathology scores were significantly higher in the SOS than the control group (median 22 vs 2, P = 0.024). No gross morphologic changes were seen in livers. Liver stiffness, Hounsfield Unit values, and iodine concentrations were higher in the SOS compared to the control group on days 10 and 20 (all, P ≤ 0.007). Compared to day 0, liver stiffness and perfusion parameters were higher on day 20 in the SOS group (all, P ≤ 0.001). Correlation coefficients for liver stiffness (r = 0.635), Hounsfield Unit values (r = 0.587), and iodine concentration (r = 0.611) with final pathology scores were positive without significance (all, P > 0.05).

CONCLUSION

Liver stiffness and perfusion parameters were significantly increased in the livers of a rabbit SOS model. SSI and DECT might aid in early diagnosis of hepatic SOS.

Ultrasound-based liver elastography in the assessment of fibrosis

Ultrasound-based elastography has rapidly replaced the need for liver biopsy in most patients with chronic liver disease in recent years. The technique is now widely supported by many manufacturers. This review will introduce various current ultrasound-based elastography techniques, review the physics and scanning techniques, discuss potential cofounding factors as well as summarising the evidence for its use in staging liver fibrosis using shear-wave elastography among different disease aetiologies. Future challenges and directions will be also be discussed.

Liver stiffness measured by acoustic radiation force impulse elastography predicted prognoses of hepatocellular carcinoma after radiofrequency ablation

The prognostic factors of patients who undergo radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC) is not fully elucidated. We aimed to investigate the role of liver stiffness (LS) and spleen stiffness (SS) measured by acoustic radiation force impulse (ARFI) elastography in determining the prognoses of patients with HCC after RFA. We prospectively enrolled 173 patients with HCC who underwent ARFI elastography for measurement of LS and SS on the same day of RFA. Overall survival (OS), recurrence-free survival (RFS) after adjusting for competing mortality, and presence of hepatic decompensation were investigated. Patients with LS > 1.5 m/s had significantly shorter OS and RFS than their counterparts. Anti-viral treatment (hazard ratio [HR]: 0.396, p = 0.015) and LS > 1.5 m/s (HR 4.105, p = 0.028) correlated with OS by a multivariate analysis. Besides, serum alpha fetoprotein >10 ng/mL and LS > 1.5 m/s independently predicted poorer RFS. On the other hand, anti-viral treatment (HR: 0.315, p = 0.010), creatinine > 1.5 mg/dL (HR: 9.447, p = 0.006), and SS > 2.7 m/s (HR: 2.869, p = 0.044) predicted a higher risk of hepatic decompensation. In conclusion, LS but not SS measured by ARFI elastography predicted tumor recurrence and OS in RFA-treated HCC; whereas, SS predicted development of hepatic decompensation in these patients.

Liver fibrosis imaging: A clinical review of ultrasound and magnetic resonance elastography

Liver fibrosis is a histological hallmark of most chronic liver diseases, which can progress to cirrhosis and liver failure, and predisposes to hepatocellular carcinoma. Accurate diagnosis of liver fibrosis is necessary for prognosis, risk stratification, and treatment decision-making. Liver biopsy, the reference standard for assessing liver fibrosis, is invasive, costly, and impractical for surveillance and treatment response monitoring. Elastography offers a noninvasive, objective, and quantitative alternative to liver biopsy. This article discusses the need for noninvasive assessment of liver fibrosis and reviews the comparative advantages and limitations of ultrasound and magnetic resonance elastography techniques with respect to their basic concepts, acquisition, processing, and diagnostic performance. Variations in clinical contexts of use and common pitfalls associated with each technique are considered. In addition, current challenges and future directions to improve the diagnostic accuracy and clinical utility of elastography techniques are discussed. Level of Evidence: 5 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:25-42.

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, MI_IS = 0.67). A 30 s duration resulted in a slightly increased threshold of 1.7 MPa (MI_IS = 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 (MI_IS = 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.

Shear-Wave Dispersion Slope from US Shear-Wave Elastography: Detection of Allograft Damage after Liver Transplantation

Background Allograft damage (hepatic parenchymal damage) after liver transplant is associated with the degree of necroinflammation in graft liver. According to a recent animal study, shear-wave dispersion slope obtained at US shear-wave elastography (SWE) is associated with necroinflammatory activity in the liver. Purpose To evaluate the role of shear-wave dispersion slope in detecting allograft damage after liver transplant. Materials and Methods In this prospective study, 104 liver transplant recipients underwent percutaneous liver biopsy for allograft evaluation from December 2017 to November 2018. All participants underwent allograft SWE examination just before liver biopsy, and liver stiffness and shear-wave dispersion slope were obtained. Allograft damage was diagnosed by histopathologic analysis. Clinical and imaging factors related to liver stiffness and shear-wave dispersion slope were determined by multivariable linear regression analysis. Diagnostic performance of each variable in detecting allograft damage was evaluated by comparing area under the receiver operating curve (AUC) values. Results There were 104 study participants (35 women); median age was 56 years (interquartile range, 50-62 years). Allograft damage was found in 46 of 104 (44.2%) of participants. The median liver stiffness (8.2 kPa vs 6.3 kPa; P < .01) and shear-wave dispersion slope (14.4 [m/sec]/kHz vs 10.4 [m/sec]/kHz; P < .01) were higher in participants with allograft damage than in those without damage, respectively. Fibrosis stage was the only determinant factor for liver stiffness (coefficient, 1.8 kPa per fibrosis stage; 95% confidence interval: 0.1, 3.5; P = .03), whereas both fibrosis stage (coefficient, 1.4 [m/sec]/kHz per fibrosis stage; 95% confidence interval: 0.3, 2.6; P = .02) and necroinflammatory activity (coefficient, 1.6 [m/sec]/kHz per necroinflammatory activity grade; 95% confidence interval: 0.5, 2.7; P < .01) affected shear-wave dispersion slope. The AUC for shear-wave dispersion slope in detecting allograft damage was 0.86, which was higher than that of liver stiffness (AUC, 0.75; P < .01). Conclusion Shear-wave dispersion slope determined at US shear-wave elastography may help in detecting allograft damage after liver transplant. © RSNA, 2019 Online supplemental material is available for this article.

Accuracy and precision of ultrasound shear wave elasticity measurements according to target elasticity and acquisition depth: A phantom study

OBJECTIVE

To investigate the accuracy and precision of ultrasound shear wave elasticity measurements as a function of target elasticity and acquisition depth.

MATERIALS AND METHODS

Using five ultrasound systems (VTQ, VTIQ, EPIQ 5, Aixplorer, and Aplio 500), two operators independently measured shear wave elasticities in two phantoms containing five different target elasticities (8±3, 14±4, 25±6, 45±8, and 80±12 kPa) at depths of 15, 30, 35, and 60 mm. Accuracy was assessed by evaluating measurement errors and the proportions of outliers, while factors affecting accuracy were assessed using logistic regression analysis. Measurement errors were defined as differences between the measured values and 1) the margins of the target elasticity, and 2) the median values of the target elasticity. Outliers were defined as measured values outside the margins of the target elasticity. Precision was assessed by calculating the reproducibility of measurements using the within-subject coefficient of variation (wCV).

RESULTS

Mean measurement errors and the proportions of outliers were higher for high than for low target elasticities (p<0.001), but did not differ in relation to acquisition depth, either within an elastography system or across the different systems. Logistic regression analysis showed that target elasticity (p<0.001) significantly affected accuracy, whereas acquisition depth (p>0.05) did not. The wCV for the 80±12 kPa target (31.33%) was significantly higher than that for lower elasticity targets (6.96-10.43 kPa; p<0.001). The wCV did not differ across acquisition depths. The individual elastography systems showed consistent results.

CONCLUSIONS

Targets with high elasticity showed lower accuracy and lower precision than targets with low elasticity, while acquisition depth did not show consistent patterns in either accuracy or precision.

Prospective comparison of transient, point shear wave, and magnetic resonance elastography for staging liver fibrosis

OBJECTIVES

To perform head-to-head comparisons of the feasibility and diagnostic performance of transient elastography (TE), point shear-wave elastography (pSWE), and magnetic resonance elastography (MRE).

METHODS

This prospective, cross-sectional, dual-center imaging study included 100 patients with known or suspected chronic liver disease caused by hepatitis B or C virus, nonalcoholic fatty liver disease, or autoimmune hepatitis identified between 2014 and 2018. Liver stiffness measured with the three elastographic techniques was obtained within 6 weeks of a liver biopsy. Confounding effects of inflammation and steatosis on association between fibrosis and liver stiffness were assessed. Obuchowski scores and AUCs for staging fibrosis were evaluated and the latter were compared using the DeLong method.

RESULTS

TE, pSWE, and MRE were technically feasible and reliable in 92%, 79%, and 91% subjects, respectively. At univariate analysis, liver stiffness measured by all techniques increased with fibrosis stages and inflammation and decreased with steatosis. For classification of dichotomized fibrosis stages, the AUCs were significantly higher for distinguishing stages F0 vs. ≥ F1 with MRE than with TE (0.88 vs. 0.71; p < 0.05) or pSWE (0.88 vs. 0.73; p < 0.05), and for distinguishing stages ≤ F1 vs. ≥ F2 with MRE than with TE (0.85 vs. 0.75; p < 0.05). TE, pSWE, and MRE Obuchowski scores for staging fibrosis stages were respectively 0.89 (95% CI 0.85-0.93), 0.90 (95% CI 0.85-0.94), and 0.94 (95% CI 0.91-0.96).

CONCLUSION

MRE provided a higher diagnostic performance than TE and pSWE for staging early stages of liver fibrosis.

TRIAL REGISTRATION

NCT02044523 KEY POINTS: • The technical failure rate was similar between MRE and US-based elastography techniques. • Liver stiffness measured by MRE and US-based elastography techniques increased with fibrosis stages and inflammation and decreased with steatosis. • MRE provided a diagnostic accuracy higher than US-based elastography techniques for staging of early stages of histology-determined liver fibrosis.

Assessment of liver fibrosis using 2-dimensional shear wave elastography: a prospective study of intra- and inter-observer repeatability and comparison with point shear wave elastography

PURPOSE

The purpose of this study was to prospectively investigate the intra- and interobserver repeatability of a new 2-dimensional (2D) shear wave elastography (SWE) technique (S-Shearwave Imaging) for assessing liver fibrosis in chronic liver disease patients, and to compare liver stiffness measurements (LSMs) made using 2D-SWE with those made using point SWE (pSWE).

METHODS

This prospective study received institutional review board approval and informed consent was obtained from all patients. Fifty-three chronic liver disease patients were randomly allocated to group 1 (for intra-observer repeatability [n=33]) or group 2 (for inter-observer repeatability [n=20]). In group 1, two 2D-SWE sessions and one pSWE sessions were performed by one radiologist. In group 2, one 2D-SWE session and one pSWE session were performed by the aforementioned radiologist, and a second 2D-SWE session was performed by another radiologist. The intraclass correlation coefficient (ICC) was used to assess intra- and interobserver reliability. LSMs obtained using 2D-SWE and pSWE were compared and correlated using the paired t test and Pearson correlation coefficient, respectively.

RESULTS

LSMs made using 2D-SWE demonstrated excellent intra- and inter-observer repeatability (ICC, 0.997 [95% confidence interval, 0.994 to 0.999]) and 0.995 [0.988 to 0.998], respectively). LSMs made using 2D-SWE were significantly different from those made using pSWE (2.1±0.6 m/sec vs. 1.9±0.6 m/sec, P<0.001), although a significant correlation existed between the 2D-SWE and pSWE LSMs (rho=0.836, P<0.001).

CONCLUSION

S-Shearwave Imaging demonstrated excellent intra- and inter-observer repeatability, and a strong correlation with pSWE measurements of liver stiffness. However, because of the significant difference between LSMs obtained using 2D-SWE and pSWE, these methods should not be used interchangeably.

Intra- and inter-operator reproducibility of US point shear-wave elastography in various organs: evaluation in phantoms and healthy volunteers

PURPOSE

This study was conducted in order to assess the intra- and interoperator reproducibility of shear-wave speed (SWS) measurement on elasticity phantoms and healthy volunteers using ultrasound-based point shear-wave elastography.

MATERIALS AND METHODS

This study was approved by the institutional review board. Two operators measured the SWS of five elasticity phantoms and seven organs (thyroid, lymph node, muscle, spleen, kidney, pancreas, and liver) of 30 healthy volunteers with 1.0-4.5 MHz convex (4C1) and 4.0-9.0 MHz linear (9L4) transducers. The phantom measurements were repeated ten times, while the volunteer measurements were performed five times each. Intra- and interoperator reproducibility was assessed. Interoperator reproducibility was also evaluated with the 95% Bland-Altman limits of agreement (LOA).

RESULTS

In phantoms, all intraclass correlation coefficients (ICCs) were above 0.90 and the 95% LOA between the two operators were less than ± 18%. In volunteers, intraoperator ICCs were > 0.75 for all regions except the pancreas. Interoperator ICC was above 0.75 for the right lobe of the liver (depth 4 cm) and the kidney, but the 95% LOA was less than ± 25% only for the liver.

CONCLUSION

Although excellent in phantoms, interoperator reproducibility was insufficient for all regions in the volunteers other than the right hepatic lobe at a depth of 4 cm. Clinicians should be aware of the 95% LOA when using SWS in patients.

KEY POINTS

• Our phantom study indicated a high reproducibility for shear-wave speed (SWS) measurements with point shear-wave elastography (pSWE). • In volunteers, intraoperator reproducibility was generally high, but the interoperator reproducibility was not high enough except for the right hepatic lobe at 4 cm depth. • To evaluate interoperator reproducibility, the 95% limits of agreement (LOA) between operators should be considered in addition to the intraclass correlation coefficient (ICC).

Non-invasive response prediction in prophylactic carvedilol therapy for cirrhotic patients with esophageal varices

BACKGROUND & AIMS

Non-selective beta-blockers (NSBBs) are the mainstay of primary prophylaxis of esophageal variceal bleeding in patients with liver cirrhosis. We investigated whether non-invasive markers of portal hypertension correlate with hemodynamic responses to NSBBs in cirrhotic patients with esophageal varices.

METHODS

In this prospective cohort study, 106 cirrhotic patients with high-risk esophageal varices in the derivation cohort received carvedilol prophylaxis, and completed paired measurements of hepatic venous pressure gradient, liver stiffness (LS), and spleen stiffness (SS) at the beginning and end of dose titration. LS and SS were measured using acoustic radiation force impulse imaging. A prediction model for hemodynamic response was derived, and subject to an external validation in the validation cohort (63 patients).

RESULTS

Hemodynamic response occurred in 59 patients (55.7%) in the derivation cohort, and in 33 patients (52.4%) in the validation cohort, respectively. Multivariate logistic regression analysis identified that ΔSS was the only significant predictor of hemodynamic response (odds ratio 0.039; 95% confidence interval 0.008-0.135; p <0.0001). The response prediction model (Model_ΔSS = 0.0490-2.8345 × ΔSS; score = (exp[Model_ΔSS])/(1 + exp[Model_ΔSS]) showed good predictive performance (area under the receiver-operating characteristic curve [AUC] = 0.803) using 0.530 as the threshold value. The predictive performance of the Model_ΔSS in the validation set improved using the same threshold value (AUC = 0.848).

CONCLUSION

A new model based on dynamic changes in SS exhibited good performance in predicting hemodynamic response to NSBB prophylaxis in patients with high-risk esophageal varices.

LAY SUMMARY

Non-selective beta-blockers are the mainstay of primary prophylaxis to prevent variceal bleeding in patients with cirrhosis and high-risk esophageal varices. This prospective study showed that a prediction model based on changes in spleen stiffness before vs. after dose titration might be a non-invasive marker for response to prophylactic non-selective beta-blocker (carvedilol) therapy in patients with cirrhosis and high-risk esophageal varices. ClinicalTrials.gov Identifier: NCT01943318.

Liver Ultrasound Elastography: An Update to the World Federation for Ultrasound in Medicine and Biology Guidelines and Recommendations

The World Federation for Ultrasound in Medicine and Biology has produced these guidelines for the use of elastography techniques in liver diseases. For each available technique, the reproducibility, results and limitations are analyzed, and recommendations are given. This set of guidelines updates the first version, published in 2015. Since the prior guidelines, there have been several advances in technology. The recommendations are based on the international published literature, and the strength of each recommendation is judged according to the Oxford Centre for Evidence-Based Medicine. The document has a clinical perspective and is aimed at assessing the usefulness of elastography in the management of liver diseases.

Comparison of acoustic radiation force impulse elastography and transient elastography for prediction of hepatocellular carcinoma recurrence after radiofrequency ablation

BACKGROUND

To compare the clinical value of acoustic radiation force impulse (ARFI) elastography and transient elastography (TE) for hepatocellular carcinoma (HCC) recurrence prediction after radiofrequency ablation (RFA) and to investigate other predictors of HCC recurrence.

PATIENTS AND METHODS

Between 2011 and 2016, 130 patients with HCC who underwent ARFI elastography and TE within 6 months before curative RFA were prospectively enrolled. Independent predictors of HCC recurrence were analyzed separately using ARFI elastography and TE. ARFI elastography and TE accuracy to predict HCC recurrence was determined by receiver operating characteristic curve analysis.

RESULTS

Of all included patients (91 men; mean age, 63.5 years; range: 43-84 years), 51 (42.5%) experienced HCC recurrence during the follow-up period (median, 21.9 months). In multivariable analysis using ARFI velocity, serum albumin and ARFI velocity [hazard ratios: 2.873; 95% confidence interval (CI): 1.806-4.571; P<0.001] were independent predictors of recurrence, and in multivariable analysis using TE value, serum albumin and TE value (hazard ratios: 1.028; 95% CI: 1.013-1.043; P<0.001) were independent predictors of recurrence. The area under the receiver operating characteristic curve of ARFI elastography (0.821; 95% CI: 0.747-0.895) was not statistically different from that of TE (0.793; 95% CI: 0.712-0.874) for predicting HCC recurrence (P=0.827). The optimal ARFI velocity and TE cutoff values were 1.6 m/s and 14 kPa, respectively.

CONCLUSION

ARFI elastography and TE yield comparable predictors of HCC recurrence after RFA.

Role of two-dimensional shear wave elastography in chronic liver diseases: A narrative review

Liver biopsy is the gold standard for evaluating the degree of liver fibrosis in patients with chronic liver disease. However, due to the many limitations of liver biopsy, there has been much interest in the use of noninvasive techniques for this purpose. Among these techniques real-time two-dimensional shear wave elastography (2D-SWE) has the advantage of measuring tissue elasticity with the guidance of B-mode images. Recently, many studies have been conducted on the application of 2D-SWE in patients with various liver diseases, and their validity has been confirmed. Here, we briefly discuss the role of 2D-SWE in patients with chronic liver diseases, particularly aspects of the examination techniques and clinical applications.

Imaging of Hepatic Fibrosis

PURPOSE OF REVIEW

The purpose of this review is to discuss the current imaging techniques for non-invasive assessment of liver fibrosis (LF).

RECENT FINDINGS

Elastography-based techniques are the most widely used imaging methods for the evaluation of LF. Currently, MR elastography (MRE) is the most accurate non-invasive method for detection and staging of LF. Ultrasound-based vibration-controlled transient elastography (VCTE) is the most widely used as it can be easily performed at the point of care but has technical limitations especially in the obese. Innovations and technical improvements continue to evolve in elastography for improving accuracy and avoiding misinterpretation from confounding factors. Other imaging methods including diffusion-weighted imaging (DWI), hepatocellular contrast-enhanced (HCE) MRI, T1 relaxometry, T1ρ imaging, textural analysis, liver surface nodularity, susceptibility-weighted imaging, and perfusion imaging are promising but need further evaluation and clinical validation. MRE is the most accurate imaging technique for assessment of LF.

On Patient Related Factors and Their Impact on Ultrasound-Based Shear Wave Elastography of the Liver

The aim of the study was to investigate patient-related factors associated with either reliable or poorly reliable measurement results of ultrasound-based shear wave elastography (SWE) of the liver. A total of 188 patients were analyzed prospectively with binary logistic regression using the interquartile range/median as cutoff to define two groups based on reliable and poorly reliable SWE results. SWE results correlated significantly with liver biopsy. Factors associated with reliable SWE results (i.e., no negative impact on measurements) were age, sex, cirrhosis, antiviral and/or cardiovascular medication, smoking habits and body mass index. Factors associated with poorly reliable SWE results were increased skin-to-liver capsule distance (odds ratio = 3.08, 95% confidence interval: 1.70-5.60) and steatosis (odds ratio = 2.89, 95% confidence interval: 1.33-6.28). These findings indicate that the interquartile range/median as a quality parameter is useful in avoiding poorly reliable SWE results. How best to examine patients with increased skin-to-liver capsule distance is a matter of some controversy, as the incidences of obesity, diabetes and metabolic syndrome are increasing worldwide; however, our results indicate that reliable SWE results can be obtained in this group of patients by using ultrasound-based SWE.

Quantitative Elastography Methods in Liver Disease: Current Evidence and Future Directions

Chronic liver diseases often result in the development of liver fibrosis and ultimately, cirrhosis. Treatment strategies and prognosis differ greatly depending on the severity of liver fibrosis, thus liver fibrosis staging is clinically relevant. Traditionally, liver biopsy has been the method of choice for fibrosis evaluation. Because of liver biopsy limitations, noninvasive methods have become a key research interest in the field. Elastography enables the noninvasive measurement of tissue mechanical properties through observation of shear-wave propagation in the tissue of interest. Increasing fibrosis stage is associated with increased liver stiffness, providing a discriminatory feature that can be exploited by elastographic methods. Ultrasonographic (US) and magnetic resonance (MR) imaging elastographic methods are commercially available, each with their respective strengths and limitations. Here, the authors review the technical basis, acquisition techniques, and results and limitations of US- and MR-based elastography techniques. Diagnostic performance in the most common etiologies of chronic liver disease will be presented. Reliability, reproducibility, failure rate, and emerging advances will be discussed. ^© RSNA, 2018 Online supplemental material is available for this article.

Principles of ultrasound elastography

Tissue stiffness has long been known to be a biomarker of tissue pathology. Ultrasound elastography measures tissue mechanical properties by monitoring the response of tissue to acoustic energy. Different elastographic techniques have been applied to many different tissues and diseases. Depending on the pathology, patient-based factors, and ultrasound operator-based factors, these techniques vary in accuracy and reliability. In this review, we discuss the physical principles of ultrasound elastography, discuss differences between different ultrasound elastographic techniques, and review the advantages and disadvantages of these techniques in clinical practice.

Liver Stiffness Measured by Two-Dimensional Shear-Wave Elastography: Prognostic Value after Radiofrequency Ablation for Hepatocellular Carcinoma

PURPOSE

To evaluate the prognostic value of liver stiffness (LS) measured using two-dimensional (2D) shear-wave elastography (SWE) in patients with hepatocellular carcinoma (HCC) treated by radiofrequency ablation (RFA).

METHODS

The Institutional Review Board approved this retrospective study and informed consent was obtained from all patients. A total of 134 patients with up to 3 HCCs ≤5 cm who had undergone pre-procedural 2D-SWE prior to RFA treatment between January 2012 and December 2013 were enrolled. LS values were measured using real-time 2D-SWE before RFA on the procedural day. After a mean follow-up of 33.8 ± 9.9 months, we analyzed the overall survival after RFA using the Kaplan-Meier method and Cox proportional hazard regression model. The optimal cutoff LS value to predict overall survival was determined using the minimal p value approach.

RESULTS

During the follow-up period, 22 patients died, and the estimated 1- and 3-year overall survival rates were 96.4 and 85.8%, respectively. LS measured by 2D-SWE was found to be a significant predictive factor for overall survival after RFA of HCCs, as was the presence of extrahepatic metastases. As for the optimal cutoff LS value for the prediction of overall survival, it was determined to be 13.3 kPa. In our study, 71 patients had LS values ≥13.3 kPa, and the estimated 3-year overall survival was 76.8% compared to 96.3% in 63 patients with LS values <13.3 kPa. This difference was statistically significant (hazard ratio = 4.30 [1.26-14.7]; p = 0.020).

CONCLUSION

LS values measured by 2D-SWE was a significant predictive factor for overall survival after RFA for HCC.

Risk stratification of thyroid nodules with Bethesda category III results on fine-needle aspiration cytology: The additional value of acoustic radiation force impulse elastography

To assess the value of conventional ultrasound, conventional strain elastography (CSE) and acoustic radiation force impulse (ARFI) elastography in differentiating likelihood of malignancy for Bethesda category III thyroid nodules. 103 thyroid nodules with Bethesda category III results on fine-needle aspiration cytology (FNAC) in 103 patients were included and all were pathologically confirmed after surgery. Conventional ultrasound, CSE and ARFI elastography including ARFI imaging and point shear wave speed (SWS) measurement were performed. Univariate and multivariate analyses were performed to identify the independent factors associated with malignancy. Area under the receiver operating characteristic curve (Az) was calculated to assess the diagnostic performance. Pathologically, 65 nodules were benign and 38 were malignant. Significant differences were found between benign and malignant nodules in ARFI. The cut-off points were ARFI imaging grade ≥ 4, SWS > 2.94 m/s and SWS ratio > 1.09, respectively. ARFI imaging (Az: 0.861) had the highest diagnostic performance to differentiate malignant from benign nodules, following by conventional ultrasound (Az: 0.606 - 0.744), CSE (Az: 0.660) and point SWS measurement (Az: 0.725 - 0.735). Multivariate logistic regression analysis showed that ARFI imaging grade ≥ 4 was the most significant independent predictor. The combination of ARFI imaging with point SWS measurement significantly improved the specificity (100% vs. 80.0%) and positive predictive value (100 % vs. 72.9%) in comparison with ARFI imaging alone. ARFI elastography is a useful tool in differentiating malignant from benign thyroid nodules with Bethesda category III results on FNAC.

Steatosis severity affects the diagnostic performances of noninvasive fibrosis tests in nonalcoholic fatty liver disease

BACKGROUND & AIMS

Nonalcoholic fatty liver disease (NAFLD) includes a wide spectrum of heterogeneous metabolic subtypes. This study compared the diagnostic performances of noninvasive fibrosis tests in predicting advanced fibrosis among patients with NAFLD and examined the effects of the subgroups on their diagnostic performances.

METHODS

Three hundred fifteen patients with biopsy-proven NAFLD were prospectively enrolled. Acoustic radiation force impulse imaging (ARFI) was performed to obtain liver stiffness measurements (LSMs). The aspartate aminotransferase-to-alanine aminotransferase ratio (AAR), aspartate aminotransferase-to-platelet ratio index (APRI), fibrosis 4 index (FIB-4), NAFLD fibrosis score (NFS) and BARD score were calculated. The diagnostic performances of noninvasive fibrosis tests were evaluated using the area under the receiver operating characteristic curve (AUROC).

RESULTS

Fibrosis 4 index (FIB-4) showed the highest AUROC for advanced fibrosis (0.866; 95% CI, 0.811-0.922). AUROC subgroup analyses were performed to assess the effects of the subgroups on diagnostic performance. For patients with advanced fibrosis, the APRI, BARD, FIB-4 and NFS AUROCs were significantly different among the radiological steatosis grades. Additionally, the AUROC of ARFI tended to decrease with increasing radiological steatosis severity. FIB-4 and NFS showed significantly lower AUROCs for advanced fibrosis in obese NAFLD than in nonobese NAFLD (P = .002 and P < .001 respectively). However, only radiological steatosis severity was independently associated with advanced fibrosis in multivariable analysis.

CONCLUSIONS

Steatosis severity may affect the diagnostic performances of noninvasive fibrosis tests in patients with NAFLD. The application of different tools should be tailored for various NAFLD subgroups to optimize noninvasive fibrosis assessments.

Comparison of Tissue Stiffness Using Shear Wave Elastography in Men with Normal Testicular Tissue, Testicular Microlithiasis and Testicular Cancer

Objectives

To compare elastography measurements in men with normal testicular tissue, testicular microlithiasis and testicular cancer.

Methods

A total of 248 consecutive patients were included. All men provided written informed consent. Testicular stiffness was assessed using shear wave elastography (SWE). Three SWE velocity measurements were assessed in each testicle. The patients were divided into three groups; men with normal testicular tissue (n=130), men with testicular microlithiasis (n=99) and men with testicular cancer (n=19).

Results

We found a higher mean velocity in the group of patients with testicular cancer (1.92 m/s (95% CI 1.82-2.03)) compared to both the group with normal tissue (0.76 m/s (95% CI: 0.75-0.78)) (p<0.001) and the group with testicular microlithiasis 0.79 m/s (95% CI: 0.77-0.81) (p<0.001).

Conclusion

The presence of testicular microlithiasis increased stiffness slightly, but within the range of variation in normal testicles. Increased stiffness may indicate testicular malignancy in testicular lesions. Ultrasound elastography could be a very useful tool when investigating scrotum.

Noninvasive assessment of hepatic sinusoidal obstructive syndrome using acoustic radiation force impulse elastography imaging: A proof-of-concept study in rat models

OBJECTIVES

To determine the feasibility of acoustic radiation force impulse (ARFI) elastography in the evaluation of hepatic sinusoidal obstruction syndrome (SOS) in rat models.

METHODS

Rat SOS models of various severities were created by monocrotaline gavage (n = 40) or by intraperitoneal injection of 5-fluorouracil, leucovorin and oxaliplatin (FOLFOX) (n = 16). Liver shear-wave velocity (SWV) was measured using ARFI elastography. Liver samples were analysed for the SOS score, steatosis, lobular inflammation and fibrosis.

RESULTS

The liver SWV was significantly elevated in the SOS models (1.29-2.24 m/s) compared with that of the matched control rats (1.01-1.09; p≤.09; veFor seven FOLFOX-treated rats which were longitudinally followed-up, the liver SWV significantly increased at 7 weeks (1.32±0.13 m/s) compared with the baseline (1.08±0.1 m/s, p=.015) and then significantly declined after a 2-week, treatment-free period (1.15±0.13 m/s; p=.048). Multivariate analysis revealed that the SOS score (p<.001) and lobular inflammation (p=.044) were independently correlated with the liver SWV.

CONCLUSION

Liver SWV is elevated in SOS in proportion to the degree of sinusoidal injury and lobular inflammation in rat SOS models. ARFI elastography has potential as an examination for diagnosis, severity assessment and follow-up of SOS.

KEY POINTS

• Liver SWV using ARFI elastography was significantly elevated in SOS rat. • Sinusoidal injury and lobular inflammation grades had correlation with liver SWV. • ARFI elastography has potential for diagnosis, severity assessment, and follow-up of SOS.

Intra-Individual Comparison between 2-D Shear Wave Elastography (GE System) and Virtual Touch Tissue Quantification (Siemens System) in Grading Liver Fibrosis

Ultrasound-based shear wave elastography (SWE) has recently gained substantial attention for non-invasive assessment of liver fibrosis. The purpose of this study was to perform an intra-individual comparison between 2-D shear wave elastography (2-D-SWE with a GE system) and Virtual Touch Tissue Quantification (VTTQ with a Siemens system) to assess whether these can be used interchangeably to grade fibrosis. Ninety-three patients (51 men, 42 women; mean age, 54 y) with liver disease of various etiologies (hepatitis B virus = 47, hepatitis C virus = 22; alcohol = 6, non-alcoholic steatohepatitis = 5, other = 13) were included. Using published system-specific shear wave speed cutoff values, liver fibrosis was classified into clinically non-significant (F0/F1) and significant (≥F2) fibrosis. Results indicated that intra-modality repeatability was excellent for both techniques (GE 2-D-SWE: intra-class correlation coefficient = 0.89 [0.84-0.93]; VTTQ: intra-class correlation coefficient = 0.90 [0.86-0.93]). Intra-modality classification agreement for fibrosis grading was good to excellent (GE 2-D-SWE: κ = 0.65, VTTQ: κ = 0.82). However, inter-modality agreement for fibrosis grading was only fair (κ = 0.31) using published system-specific shear wave speed cutoff values of fibrosis. In conclusion, although both GE 2-D-SWE and Siemens VTTQ exhibit good to excellent intra-modality repeatability, inter-modality agreement is only fair, suggesting that these should not be used interchangeably.

Prospective comparison among transient elastography, supersonic shear imaging, and ARFI imaging for predicting fibrosis in nonalcoholic fatty liver disease

The diagnostic performance of supersonic shear imaging (SSI) in comparison with those of transient elastography (TE) and acoustic radiation force impulse imaging (ARFI) for staging fibrosis in nonalcoholic fatty liver disease (NAFLD) patients has not been fully assessed, especially in Asian populations with relatively lean NAFLD compared to white populations. Thus, we focused on comparing the diagnostic performances of TE, ARFI, and SSI for staging fibrosis in a head-to-head manner, and identifying the clinical, anthropometric, biochemical, and histological features which might affect liver stiffness measurement (LSM) in our prospective biopsy-proven NAFLD cohort. In this study, ninety-four patients with biopsy-proven NAFLD were included prospectively. Liver stiffness was measured using TE, SSI, and ARFI within 1 month of liver biopsy. The diagnostic performance for staging fibrosis was assessed using receiver operating characteristic (ROC) analysis. Anthropometric data were evaluated as covariates influencing LSM by regression analyses. Liver stiffness correlated with fibrosis stage (p < 0.05); the area under the ROC curve of TE (kPa), SSI (kPa), and ARFI (m/s) were as follows: 0.757, 0.759, and 0.657 for significant fibrosis and 0.870, 0.809, and 0.873 for advanced fibrosis. Anthropometric traits were significant confounders affecting SSI, while serum liver injury markers significantly confounded TE and ARFI. In conclusion, the LSM methods had similar diagnostic performance for staging fibrosis in patients with NAFLD. Pre-LSM anthropometric evaluation may help predict the reliability of SSI.

Real-time two-dimensional Shear-wave elastography for liver stiffness in children: Interobserver variation and effect of breathing technique

OBJECTIVES

To evaluate interobserver variation and to assess the effect of the breathing technique on liver stiffness (LS) measurement using real-time two-dimensional shear-wave elastography (2D-SWE) in children.

METHODS

Patients who underwent real-time 2D-SWE by two operators (group 1) and patients who underwent real-time 2D-SWE by one operator using the free-breathing and breath-holding techniques (group 2) were included. In group 1, interobserver agreement was assessed using the intraclass correlation coefficient (ICC) and the 95% limits-of-agreement was analyzed to evaluate the maximum change in the LS values based on Bland-Altman analysis. In group 2, the Bland-Altman plot and the paired t-test were used to determine the effect of breathing technique on LS measurement.

RESULTS

The interobserver agreement of the LS measurement in group 1 (n=63) was excellent (ICC, 0.953), and the 95% limits-of-agreement was 31.8% of the mean LS values. In group 2 (n=45), the free-breathing technique revealed systematically lower LS with a mean difference of -11.1% of the mean LS values, compared to the breath-holding technique (P=0.016).

CONCLUSION

LS measurement assessed by real-time 2D-SWE in children showed excellent interobserver agreement. Changes in LS values less than 31.8% of the mean LS values may represent the measurement error. The free-breathing technique showed lower LS values, compared to the breath-holding technique.

Accurate measurements of liver stiffness using shear wave elastography in children and young adults and the role of the stability index

Purpose

The purpose of this study was to evaluate the usefulness of the stability index (SI) in liver stiffness measurements using shear wave elastography (SWE) in children.

Methods

A total of 29 children and young adults (mean age, 16.1 years; range, 8 to 28 years; 11 boys and 18 girls) who underwent liver stiffness measurements using SWE under free-breathing and breath-holding conditions were included in our study. Ten SWE measurements were acquired in each of four groups: free-breathing and breath-holding, and with and without using the SI. The failure rate of acquisition of SI values over 90% was calculated in each group. To evaluate variability in the SWE measurements, the standard deviation, coefficient of variation, and percentage of unreliable measurements were compared. Intraobserver agreement and the optimal minimal number of measurements were calculated using intraclass correlation coefficients.

Results

A failure to acquire SI values over 90% was observed in 17% of the scans in the free-breathing group and in 7% of the scans in the breath-holding group. In both groups, utilizing the SI led to a significantly lower standard deviation and coefficient of variation. When using the SI, the percentage of unreliable measurements decreased from 16.7% to 8.3% in the free-breathing group and 14.8% to 0% in the breath-holding group. With the use of the SI, intraobserver agreement increased and the optimal minimal number of repeated measurements decreased in both the free-breathing and breath-holding groups.

Conclusion

Utilization of the SI in the measurement of liver SWE in children reduced measurement variability and increased reliability in both free-breathing and breath-holding conditions.

Comparison of 2-D Shear Wave Elastography and Transient Elastography for Assessing Liver Fibrosis in Chronic Hepatitis B

This study compared 2-D shear wave elastography (SWE) and transient elastography (TE) for liver fibrosis staging in patients with chronic hepatitis B (CHB) infection using liver biopsy as the reference standard. Patients with CHB infection who underwent liver biopsy were consecutively included. After exclusions, 257 patients were analyzed. Two-dimensional SWE resulted in a significantly higher rate of reliable measurements (98.1%, 252/257) than TE (93.0%, 239/257) (p = 0.011). Liver stiffness measurements of the two examinations exhibited a strong correlation (r = 0.835, p < 0.001). In patients given a confirmed histologic diagnosis, Spearman's rank coefficients were 0.520 in stage F0 (p < 0.001), 0.684 in stage F1 (p < 0.001), 0.777 in stage F2 (p < 0.001), 0.672 in stage F3 (p < 0.001) and 0.755 in stage F4 (p < 0.001). There were no significant differences between the areas under the receiver operating characteristic (ROC) curves of 2-D SWE and TE for liver fibrosis staging (all p values > 0.05). Two-dimensional SWE had diagnostic accuracy comparable to that of TE for liver fibrosis staging. The measurements that the two techniques provide are not interchangeable.

Reproducibility of 2-Dimensional Shear Wave Elastography Assessment of the Liver: A Direct Comparison With Point Shear Wave Elastography in Healthy Volunteers

OBJECTIVES

Two-dimensional shear wave elastography (2D-SWE) imaging for the noninvasive assessment of tissue stiffness was assessed for reproducibility in healthy volunteers in quantifying liver elasticity, compared with an established point shear wave elastography (p-SWE) technique also known as virtual touch quantification (VTQ) (SIEMENS).

METHODS

Eleven healthy volunteers were examined by four experienced operators on two occasions, separated by two weeks (sessions A and B). Ten 2D-SWE using LOGIQ E9 and p-SWE measurements using VTQ (in meters per second) were consecutively taken from deep portions of liver segments 5 or 6 away from vascular structures, using standard techniques. Inter- and intra-observer agreement was assessed by intraclass coefficient (ICC).

RESULTS

A total of 880 2D-SWE and p-SWE velocities were recorded. Mean values from the four operators ranged between 1.188 and 1.196 m/s for 2D-SWE and 1.170 to 1.207 m/s for p-SWE. Interobserver reproducibility was good for both sessions with ICCs of 0.88 and 0.93 (2D-SWE) and 0.87 and 0.93 (p-SWE). The overall intra-operator reproducibility between sessions A and B was good for both p-SWE and 2D-SWE with ICC of 0.87 and 0.83, respectively. For inter- and intra-observer variability, the ICC was more than or equal to 0.71, indicating that the results were reliable. There was a strong and significant correlation between the 2D-SWE and p-SWE measurements (r = 0.87, P = .0006), but their velocities did not agree equally across different velocities.

CONCLUSIONS

Two-dimensional SWE using LOGIQ E9 is a reliable and reproducible method for measuring elasticity in healthy volunteers and has a similar degree of reliability as p-SWE using VTQ, but absolute measurements from the two techniques should not be used interchangeably.