Ultrasound of Diffuse Liver Disease Including Elastography

Triglyceride-glucose index is independently associated with fatty pancreas disease in Chinese elderly

OBJECTIVE

To determine the prevalence of fatty pancreas disease (FPD) diagnosed by transabdominal ultrasound in Chinese elderly aged 65 years and above to explore the correlation between triglyceride glucose index (TyG index) and FPD and its severity, and to evaluate the ability of TyG index to identify FPD and its severity.

METHODS

The study population was derived from the Thyroid Diseases in Older Population: Screening, Surveillance, and Intervention (TOPS) study conducted in the iodine-adapted areas of Jiangsu Province from May to July 2021. A total of 567 participants aged 65 years and above in rural areas were included in the final analysis. TyG index was calculated by the established formula: Ln [TG (mg/dL) × FBG (mg/dL)/2]. FPD and the degree of intra-pancreatic fat deposition (IPFD) were diagnosed by abdominal ultrasound. The logistic regression model was performed to determine the correlation between clinical parameters, including TyG index, and FPD and its severity. The diagnostic power of TyG index was assessed by receiver operating characteristic curve (ROC).

RESULTS

Overall, 72.66% (412/567) of subjects had FPD, of which over half had moderate to severe FPD. The proportions of overweight, obesity, NAFLD, and dyslipidemia were significantly higher in the moderate-to-severe FPD group than in the mild FPD group. Multivariate logistic regression showed that TyG index was independently associated with FPD in the elderly population, but was not significantly associated with the severity of IPFD. As the level of TyG index increased, the metabolic disorders in the population worsened and the prevalence of FPD increased significantly. TyG index had a good diagnostic performance for FPD. The combination of BMI or NAFLD and TyG index improved the diagnostic ability for FPD.

CONCLUSION

The prevalence of FPD diagnosed by abdominal ultrasound is high in the elderly aged 65 years and above in rural areas in China. TyG index has good identification of FPD but poor recognition of the severity of IPFD. TyG index, when combined with other clinical parameters, may have more diagnostic advantages.

The Effect of Backscatter Anisotropy in Assessing Hepatic Steatosis Using Ultrasound Hepatorenal Index

OBJECTIVES

To discuss challenges in assessing hepatic steatosis using ultrasound hepatorenal index (HRI).

METHODS

We retrospectively analyzed HRI and liver magnetic resonance imaging-based proton density fat fraction (MRI-PDFF) in 134 adult participants (53 men and 81 women, mean age 55 years). The diagnostic performance of HRI for determining hepatic steatosis was tested by the area under the receiver operating characteristic curve (AUROC) using liver MRI-PDFF as the reference. Regression plots were employed to compare the sampling sites in liver and kidney that were used to calculate HRIs.

RESULTS

In 11 of 134 cases (8.2%), we failed to acquire HRI measurements. In the remaining 123 cases, AUROC for HRI (cutoff: 1.69 ± 0.13 [mean ± standard deviation]) for defining the HRI threshold for diagnosing hepatic steatosis was 0.83. In 60 of 123 cases (49%) with HRI measurement IQR/median >0.3, slopes of the regression lines in the liver showed backscatter intensity changes consistent with signal attenuation. However, in the kidney, the backscatter intensity was inverted yielding position-dependent HRI cutoff values, mid-pole = 2.24 ± 0.20 and upper pole = 1.08 ± 0.16.

CONCLUSIONS

HRI is used to estimate liver steatosis based on backscattered ultrasound. In order to compensate for effects such as body habitus and transducer frequency, the liver backscatter is divided by backscatter from a corresponding region at the same depth in the right renal cortex. Theoretically, this compensation should make HRI sampling position independent. Yet, due to renal cortical backscatter anisotropy, this compensation method does not work in general, potentially producing inaccurate liver fat estimates.

Geophysics-Inspired Nonlinear Stress-Strain Law for Biological Tissues and Its Applications in Compression Optical Coherence Elastography

We propose a nonlinear stress-strain law to describe nonlinear elastic properties of biological tissues using an analogy with the derivation of nonlinear constitutive laws for cracked rocks. The derivation of such a constitutive equation has been stimulated by the recently developed experimental technique-quasistatic Compression Optical Coherence Elastography (C-OCE). C-OCE enables obtaining nonlinear stress-strain dependences relating the applied uniaxial compressive stress and the axial component of the resultant strain in the tissue. To adequately describe nonlinear stress-strain dependences obtained with C-OCE for various tissues, the central idea is that, by analogy with geophysics, nonlinear elastic response of tissues is mostly determined by the histologically confirmed presence of interstitial gaps/pores resembling cracks in rocks. For the latter, the nonlinear elastic response is mostly determined by elastic properties of narrow cracks that are highly compliant and can easily be closed by applied compressing stress. The smaller the aspect ratio of such a gap/crack, the smaller the stress required to close it. Upon reaching sufficiently high compressive stress, almost all such gaps become closed, so that with further increase in the compressive stress, the elastic response of the tissue becomes nearly linear and is determined by the Young's modulus of the host tissue. The form of such a nonlinear dependence is determined by the distribution of the cracks/gaps over closing pressures; for describing this process, an analogy with geophysics is also used. After presenting the derivation of the proposed nonlinear law, we demonstrate that it enables surprisingly good fitting of experimental stress-strain curves obtained with C-OCE for a broad range of various tissues. Unlike empirical fitting, each of the fitting parameters in the proposed law has a clear physical meaning. The linear and nonlinear elastic parameters extracted using this law have already demonstrated high diagnostic value, e.g., for differentiating various types of cancerous and noncancerous tissues.

Hepatic steatosis using ultrasound-derived fat fraction: First technical and clinical evaluation

OBJECTIVES

To explore the technical and clinical evaluation of ultrasound-derived fat fraction (UDFF) measurement in adult patients in whom fatty liver was suspected.

MATERIALS AND METHODS

In this prospective study, 41 participants were initially enrolled in our hospital between October 2022 and December 2022 and received UDFF assessment using Siemens ACUSON Sequoia system equipped with DAX transducer. UDFF measurement was performed three times to obtain UDFF values from each imaging location (V hepatic segment and VIII hepatic segment) per participant, and the depth (skin-to-capsule distance) was automatically measured. The echogenicity of liver tissue in B mode ultrasound (BMUS) was compared to the normal kidney tissue, and fatty liver was graded as mild (Grade 1), moderate (Grade 2), and severe (Grade 3). The median of the acquired overall median UDFF values was used for statistical analysis. All ultrasound examinations were performed by one of two radiologists (with 20 and 10 years of liver ultrasound imaging experience).

RESULTS

Finally, UDFF measurement was successfully performed on 38 participants to obtain valid values, including 21 men with a median age of 40.0 years (interquartile range [IQR]: 23.0 - 58.5) and 17 women with a median age of 60.0 years (IQR: 29.5 - 67.0). Fatty liver was diagnosed by BMUS features in 47.4% (18/38) participants. Among all participants, the median UDFF value was 7.0% (IQR: 4.0 - 15.6). A significant difference in UDFF values was found between participants with fatty liver and without fatty liver (U = 7.0, P < 0.001), and UDFF values elevated as the grade of the fatty liver increased (P < 0.001). The median UDFF values from the three UDFF measurements obtained during each ultrasound examination showed excellent agreement (ICC = 0.882 [95% confidence interval: 0.833 - 0.919]). The Spearman correlation of UDFF values in different depths was moderate, with a rs value of 0.546 (P < 0.001). No significant differences in UDFF values were found between V hepatic segment and VIII hepatic segment (U = 684.5, P = 0.697).

CONCLUSIONS

UDFF provides a novel non-invasive imaging tool for hepatic steatosis assessment with excellent feasibility.

A prospective comparison of three ultrasound-based techniques in quantitative diagnosis of hepatic steatosis in NAFLD

PURPOSE

To investigate the correlation between different ultrasound attenuation-based techniques and to compare their diagnostic performances using proton magnetic resonance spectroscopy (1H-MRS) as a reference standard.

METHODS

Participants who had clinical suspicion of nonalcoholic fatty liver disease (NAFLD) were prospectively recruited. Each subject had ultrasound with attenuation imaging (ATI) or quantitative ultrasound including tissue attenuation imaging (TAI) and tissue scatter-distribution imaging (TSI), and controlled-attenuation parameter (CAP) and 1H-MRS if available. The technical success rates, intra-observer repeatabilities of attenuation and backscattering coefficient were evaluated. ATI, TAI and CAP were three attenuation-based techniques. Spearman coefficient was used to test correlations among them and 1H-MRS. In addition, the diagnostic performances of these parameters for detecting ≥ 5% or 10% hepatic steatosis were evaluated.

RESULTS

130 participants had ultrasound scanning. Among them, 67 had CAP and 48 had 1H-MRS. The technical success rates were all 100%. The intra-observer repeatabilities of them were also excellent (ICCs > 0.90) and AC-ATI correlated well with AC-TAI (r = 0.752). AC-ATI, AC-TAI showed moderate correlation with CAP, (rATI = 0.623, 95% CI 0.446-0.752, P < 0.001; rTAI = 0.573, 95% CI 0.377-0.720, P < 0.001). For correlation with 1H-MRS, ATI and TAI performed better than CAP(rATI = 0.587; rTAI = 0.712; r CAP = 0.485). The AUCs of ATI, TAI, TSI and CAP for detecting ≥ 5% hepatic steatosis were 0.883, 0.862, 0.870 and 0.868, respectively. The AUC improved to 0.907 when TAI and TSI were combined (P < 0.05). When detecting ≥ 10% hepatic steatosis, the AUCs were 0.855, 0.702, 0.822 and 0.838, respectively.

CONCLUSION

Different ultrasound attenuation-based techniques were well correlated and exhibited good diagnostic performances in quantitative diagnosis of hepatic steatosis, however, the threshold values were different. Combinations of multiple parameters may improve the diagnostic performance in detecting hepatic steatosis.

TRIAL REGISTRATION

The study has been registered online ( https://www.chictr.org.cn ; unique identifier: ChiCTR2300069459).

Quantitative ultrasound fatty liver evaluation in a pediatric population: comparison with magnetic resonance imaging of liver proton density fat fraction

BACKGROUND

Biopsy remains the gold standard for the diagnosis of hepatic steatosis, the leading cause of pediatric chronic liver disease; however, its costs call for less invasive methods.

OBJECTIVE

This study examined the diagnostic accuracy and reliability of quantitative ultrasound (QUS) for the assessment of liver fat content in a pediatric population, using magnetic resonance imaging proton density fat fraction (MRI-PDFF) as the reference standard.

MATERIALS AND METHODS

We enrolled 36 patients. MRI-PDFF involved a 3-dimensional T2*-weighted with Dixon pulse multiple-echo sequence using iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL IQ). QUS imaging relied on the ultrasound system "RS85 A" (Samsung Medison, Seoul, South Korea) and the following software: Hepato-Renal Index with automated region of interest recommendation (EzHRI), Tissue Attenuation Imaging (TAI), and Tissue Scatter Distribution Imaging (TSI). For each QUS index, receiver operating characteristic (ROC) curve analysis against MRI-PDFF was used to identify the associated cut-off value and the area under the ROC curve (AUROC). Concordance between two radiologists was assessed by intraclass correlation coefficients (ICCs) and Bland-Altman analysis.

RESULTS

A total of 61.1% of the sample (n=22) displayed a MRI-PDFF ≥ 5.6%; QUS cut-off values were TAI=0.625 (AUROC 0.90, confidence interval [CI] 0.77-1.00), TSI=91.95 (AUROC 0.99, CI 0.98-1.00) and EzHRI=1.215 (AUROC 0.98, CI 0.94-1.00). Inter-rater reliability was good-to-excellent for EzHRI (ICC 0.91, 95% C.I. 0.82-0.95) and TAI (ICC 0.94, 95% C.I. 0.88-0.97) and moderate to good for TSI (ICC 0.73; 95% C.I. 0.53-0.85).

CONCLUSION

Our results suggest that QUS can be used to reliably assess the presence and degree of pediatric hepatic steatosis.

Evaluation of Liver and Spleen With Shear Wave Elastography in Adult Patients With Familial Mediterranean Fever

ABSTRACT

Familial Mediterranean fever (FMF) is an autoinflammatory disease and an important health problem in countries bordering the eastern Mediterranean, including Turkey. In this study, we aimed to evaluate possible tissue stiffness changes that may develop in the liver and spleen in adult FMF patients with shear wave elastography (SWE), and its usability as an auxiliary imaging method that will be able to provide additional advantage in clinical follow-up. Seventy-five adult FMF patients and 73 adult volunteer were included in the study. Examination was performed through an intercostal space where the liver and spleen were clearly visible. The parenchymal stiffness degrees of the liver and spleen were quantified by shear modulus values in kilopascals. Differences in stiffness values of the liver and spleen between the 2 groups were examined. Liver stiffness value (LSV) was found to be statistically significantly higher in the FMF group. Although the spleen stiffness value (SSV) was found higher in the FMF group, the difference between the groups was not statistically significant. Increased LSVs in patients with FMF can be quantitatively demonstrated by the 2-dimensional SWE method, and SWE may be useful as an auxiliary imaging method in the follow-up of patients with FMF for this purpose. The LSV and SSV obtained in this study may be useful as reference stiffness values for both healthy individuals and those with FMF.

Diagnostic Efficacy of Renal 2-D Shear Wave Elastography in Familial Mediterranean Fever Disease

ABSTRACT

The aims of this study were to evaluate the kidneys of patients with familial Mediterranean fever (FMF) noninvasively and quantitatively using 2-D shear wave elastography (SWE) and to reveal the diagnostic efficacy of SWE in FMF-induced renal involvement. Healthy controls, FMF patients, and FMF patients with proteinuria were included in the study, and differences in renal stiffness values between the groups were examined. In addition, a relationship between age, sex, height, weight, body mass index, serum erythrocyte sedimentation rate, C-reactive protein, glomerular filtration rate, and renal stiffness values was evaluated. A total of 120 subjects, including 60 controls, 41 FMF patients without proteinuria, and 19 FMF patients with proteinuria, were enrolled in the study. Renal stiffness values were found to be significantly higher in the group with FMF compared with the control group. In addition, the values in the proteinuria group were higher than both the control group and FMF patients without proteinuria ( P < 0.001). A significant positive correlation was found between the renal stiffness value and C-reactive protein. According to receiver operating characteristic analysis, the mean renal stiffness value was 7.905 kPa or greater to determine FMF-induced proteinuria. The current study shows that renal stiffness values were higher in FMF patients compared with the normal population and the values showed further increase in the presence of proteinuria, which indicates a more advanced stage of renal involvement of the disease. These findings reveal that SWE can be used as a noninvasive diagnostic tool in the diagnosis, follow-up, and evaluating the severity of FMF.

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.

Non-invasive evaluation of liver steatosis with imaging modalities: New techniques and applications

In the world, nonalcoholic fatty liver disease (NAFLD) accounts for majority of diffuse hepatic diseases. Notably, substantial liver fat accumulation can trigger and accelerate hepatic fibrosis, thus contributing to disease progression. Moreover, the presence of NAFLD not only puts adverse influences for liver but is also associated with an increased risk of type 2 diabetes and cardiovascular diseases. Therefore, early detection and quantified measurement of hepatic fat content are of great importance. Liver biopsy is currently the most accurate method for the evaluation of hepatic steatosis. However, liver biopsy has several limitations, namely, its invasiveness, sampling error, high cost and moderate intraobserver and interobserver reproducibility. Recently, various quantitative imaging techniques have been developed for the diagnosis and quantified measurement of hepatic fat content, including ultrasound- or magnetic resonance-based methods. These quantitative imaging techniques can provide objective continuous metrics associated with liver fat content and be recorded for comparison when patients receive check-ups to evaluate changes in liver fat content, which is useful for longitudinal follow-up. In this review, we introduce several imaging techniques and describe their diagnostic performance for the diagnosis and quantified measurement of hepatic fat content.

Updates on Quantitative MRI of Diffuse Liver Disease: A Narrative Review

Diffuse liver diseases are highly prevalent conditions around the world, including pathological liver changes that occur when hepatocytes are damaged and liver function declines, often leading to a chronic condition. In the last years, Magnetic Resonance Imaging (MRI) is reaching an important role in the study of diffuse liver diseases moving from qualitative to quantitative assessment of liver parenchyma. In fact, this can allow noninvasive accurate and standardized assessment of diffuse liver diseases and can represent a concrete alternative to biopsy which represents the current reference standard. MRI approach already tested for other pathologies include diffusion-weighted imaging (DWI) and radiomics, able to quantify different aspects of diffuse liver disease. New emerging MRI quantitative methods include MR elastography (MRE) for the quantification of the hepatic stiffness in cirrhotic patients, dedicated gradient multiecho sequences for the assessment of hepatic fat storage, and iron overload. Thus, the aim of this review is to give an overview of the technical principles and clinical application of new quantitative MRI techniques for the evaluation of diffuse liver disease.

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

Nonalcoholic fatty liver disease (NAFLD) is believed to affect one-third of American adults. Noninvasive methods that enable detection and monitoring of NAFLD have the potential for great public health benefits. Because of its low cost, portability, and noninvasiveness, US is an attractive alternative to both biopsy and MRI in the assessment of liver steatosis. NAFLD is qualitatively associated with enhanced B-mode US echogenicity, but visual measures of B-mode echogenicity are negatively affected by interobserver variability. Alternatively, quantitative backscatter parameters, including the hepatorenal index and backscatter coefficient, are being investigated with the goal of improving US-based characterization of NAFLD. The American Institute of Ultrasound in Medicine and Radiological Society of North America Quantitative Imaging Biomarkers Alliance are working to standardize US acquisition protocols and data analysis methods to improve the diagnostic performance of the backscatter coefficient in liver fat assessment. This review article explains the science and clinical evidence underlying backscatter for liver fat assessment. Recommendations for data collection are discussed, with the aim of minimizing potential confounding effects associated with technical and biologic variables.

Ultrasound Methods for the Assessment of Liver Steatosis: A Critical Appraisal

The prevalence of the non-alcoholic fatty liver disease has reached major proportions, being estimated to affect one-quarter of the global population. The reference techniques, which include liver biopsy and the magnetic resonance imaging proton density fat fraction, have objective practical and financial limitations to their routine use in the detection and quantification of liver steatosis. Therefore, there has been a rising necessity for the development of new inexpensive, widely applicable and reliable non-invasive diagnostic tools. The controlled attenuation parameter has been considered the point-of-care technique for the assessment of liver steatosis for a long period of time. Recently, many ultrasound (US) system manufacturers have developed proprietary software solutions for the quantification of liver steatosis. Some of these methods have already been extensively tested with very good performance results reported, while others are still under evaluation. This manuscript reviews the currently available US-based methods for diagnosing and grading liver steatosis, including their classification and performance results, with an appraisal of the importance of this armamentarium in daily clinical practice.

Hepatic Fat Quantification With Novel Ultrasound Based Techniques: A Diagnostic Performance Study Using Magnetic Resonance Imaging Proton Density Fat Fraction as Reference Standard

Purpose: To assess the diagnostic performances of novel Tissue attenuation imaging (TAI) and Tissue scatter distribution imaging (TSI) tools in quantification of liver fat content using magnetic resonance imaging proton density fat fraction (MRI PDFF) as reference standard. Methods: Eighty consecutive patients with known or suspected non-alcoholic fatty liver disease (NAFLD) who volunteered to participate in the study comprised the study cohort. All patients underwent MRI PDFF scan and quantitative ultrasound (QUS) imaging using TAI and TSI tools. The cutoff values of ≥5%, ≥16.3% and ≥21.7% on MRI PDFF were used for mild, moderate and severe steatosis, respectively. Area under the Receiver operating characteristic (AUROC) curves were used to assess the diagnostic performance of TAI and TSI in detecting different grades of hepatic steatosis. Results: The AUROCs of TAI and TSI tools in detecting hepatosteatosis (MRI PDFF ≥5%), were 0.95 [95% Confidence Interval (CI): 0.91–0.99] ( P < 0.001) and 0.96 (95% CI: 0.93–0.99) ( P < 0.001), respectively. In distinguishing between different grades of steatosis, the values of 0.75, 0.86 and 0.96 dB/cm/MHz have 88%, 88% and 100% sensitivity, respectively, for TAI tool; and the values of 92.44, 96.64 and 99.45 have 90%, 92% and 91.7% sensitivity, respectively, for TSI tool. Conclusion: TAI and TSI tools accurately quantify liver fat content and can be used for the assessment and grading of hepatosteatosis in patients with known or suspected NAFLD.

Correlation between hepatorenal index and attenuation imaging for assessing hepatic steatosis

INTRODUCTION

Hepatic steatosis screening is required to assess high-risk populations, identify those for intervention, monitor response and prevent disease progression and complications. Liver biopsy and magnetic resonance imaging proton density fat fraction are current gold standards, but are limited by biopsy risk factors, patient tolerance and cost. Non-invasive, cost-effective, semi-quantitative and quantitative ultrasound assessment exists. The aim of this study was to assess the correlation between the semi-quantitative hepatorenal index (HRI) to assess hepatic steatosis using the quantitative attenuation imaging (ATI) as a reference standard, in adults with varied suspected liver pathologies.

METHODS

Data were collected prospectively between April 2019 and March 2020 at a tertiary institution on any patient >18 years referred to US assessment of suspected liver pathology. The only exclusion criteria were absent or invalid HRI or ATI measurements. Three hundred fifty eight patients were included.

RESULTS

There was a significant weak positive correlation between HRI and ATI (r = 0.351, P < 0.001) and between HRI steatosis grade (SG) and ATI SG (r = 0.329, P < 0.001), using previously established cut-off values. With ATI as the reference standard, there was no significant correlation between HRI and hepatic steatosis within steatosis grades, nor for no (SG = 0) or any (SG > 0) hepatic steatosis.

CONCLUSIONS

Our study in a typical heterogeneous clinical population suggests the semi-quantitative HRI is of limited use in hepatic steatosis imaging. As HRI is the objective measure of the subjective brightness (B)-mode assessment, this imaging feature may not be as reliable as previously thought. Quantitative ATI may be the preferred non-invasive technique for hepatic steatosis assessment.

Diagnostic Modalities of Non-Alcoholic Fatty Liver Disease: From Biochemical Biomarkers to Multi-Omics Non-Invasive Approaches

Non-Alcoholic Fatty Liver Disease (NAFLD) is currently the most common cause of chronic liver disease worldwide, and its prevalence is increasing globally. NAFLD is a multifaceted disorder, and its spectrum includes steatosis to steatohepatitis, which may evolve to advanced fibrosis and cirrhosis. In addition, the presence of NAFLD is independently associated with a higher cardiometabolic risk and increased mortality rates. Considering that the vast majority of individuals with NAFLD are mainly asymptomatic, early diagnosis of non-alcoholic steatohepatitis (NASH) and accurate staging of fibrosis risk is crucial for better stratification, monitoring and targeted management of patients at risk. To date, liver biopsy remains the gold standard procedure for the diagnosis of NASH and staging of NAFLD. However, due to its invasive nature, research on non-invasive tests is rapidly increasing with significant advances having been achieved during the last decades in the diagnostic field. New promising non-invasive biomarkers and techniques have been developed, evaluated and assessed, including biochemical markers, imaging modalities and the most recent multi-omics approaches. Our article provides a comprehensive review of the currently available and emerging non-invasive diagnostic tools used in assessing NAFLD, also highlighting the importance of accurate and validated diagnostic tools.

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.

Quantification of Liver Fat Content with Ultrasound: A WFUMB Position Paper

New ultrasound methods that can be used to quantitatively assess liver fat content have recently been developed. These quantitative ultrasound (QUS) methods are based on the analysis of radiofrequency echoes detected by the transducer, allowing calculation of parameters for quantifying the fat in the liver. In this position paper, after a section dedicated to the importance of quantifying liver steatosis in patients with non-alcoholic fatty liver disease and another section dedicated to the assessment of liver fat with magnetic resonance, the current clinical studies performed using QUS are summarized. These new methods include spectral-based techniques and techniques based on envelope statistics. The spectral-based techniques that have been used in clinical studies are those estimating the attenuation coefficient and those estimating the backscatter coefficient. Clinical studies that have used tools based on the envelope statistics of the backscattered ultrasound are those performed by using the acoustic structure quantification or other parameters derived from it, such as the normalized local variance, and that performed by estimating the speed of sound. Experts' opinions are reported.

Role of Ultrasound for Chronic Liver Disease and Hepatocellular Carcinoma Surveillance

Ultrasound plays a vital role in the evaluation of patients with chronic liver disease and in hepatocellular carcinoma (HCC) surveillance in populations at risk for developing HCC. Semiannual ultrasound for HCC surveillance is universally recommended by all liver societies around the world. Advanced ultrasound techniques, such as elastography and contrast-enhanced ultrasound, offer additional benefits in imaging evaluation of chronic liver disease. Major benefits of ultrasound include its high safety profile and relatively low cost.

Noninvasive Assessment of Hepatitis C Virus Infected Patients Using Vibration-Controlled Transient Elastography

Chronic infection with hepatitis C virus (HCV) is one of the leading causes of cirrhosis and hepatocellular carcinoma (HCC). Surveillance of these patients is an essential strategy in the prevention chain, including in the pre/post-antiviral treatment states. Ultrasound elastography techniques are emerging as key methods in the assessment of liver diseases, with a number of advantages such as their rapid, noninvasive, and cost-effective characters. The present paper critically reviews the performance of vibration-controlled transient elastography (VCTE) in the assessment of HCV patients. VCTE measures liver stiffness (LS) and the ultrasonic attenuation through the embedded controlled attenuation parameter (CAP), providing the clinician with a tool for assessing fibrosis, cirrhosis, and steatosis in a noninvasive manner. Moreover, standardized LS values enable proper staging of the underlying fibrosis, leading to an accurate identification of a subset of HCV patients that present a high risk for complications. In addition, VCTE is a valuable technique in evaluating liver fibrosis prior to HCV therapy. However, its applicability in monitoring fibrosis regression after HCV eradication is currently limited and further studies should focus on extending the boundaries of VCTE in this context. From a different perspective, VCTE may be effective in identifying clinically significant portal hypertension (CSPH). An emerging prospect of clinical significance that warrants further study is the identification of esophageal varices. Our opinion is that the advantages of VCTE currently outweigh those of other surveillance methods.

Ultrasound Elastographic Measurement of Rigor Mortis in an Animal Model: A Feasibility Study for Improved Time-of-Death Estimates in Forensic Investigations

OBJECTIVE. The purpose of our study was to assess the feasibility of 2D shear wave ultrasound elastography to quantitatively measure changes of rigor mortis. SUBJECTS AND METHODS. Muscle stiffness of two live pigs and nine sacrificed pigs was measured in kilopascals using ultrasound elastography. The nine sacrificed pigs were divided into three groups of three pigs each and placed in one of three environments at 90°F (32°C), 70°F (21°C), or 34°F (1°C). Ultrasound elastography of five muscles was performed at 1- to 2-hour intervals for up to 50 hours postmortem. For each pig and muscle location, the time to start, peak intensity, duration of peak, and time to decline of rigor mortis were identified from the graphs of muscle stiffness values over time. These outcome variables were then compared across ambient temperature, body weight, and age groups using the Wilcoxon rank sum test. RESULTS. Postmortem measurements show a rise, peak, and decline of muscle stiffness after death. Rigor mortis was highly significantly affected by ambient temperature (p < .001), was significantly affected by body weight (p = .04), and was not significantly affected by animal age or muscle location (facial vs truncal vs limb) (p > .50). Peak intensity of rigor mortis developed more quickly but attained lower levels of muscle stiffness at 90°F (80-100 kPa) compared with 70°F and 34°F (280-300 kPa) (p < .001). The duration of peak rigor mortis and the time to decline of rigor mortis were significantly longer for the lower temperatures (p < .001). CONCLUSION. Two-dimensional shear wave ultrasound elastography can quantifi-ably measure the trajectory of rigor mortis in an animal model. This new approach may have direct implications for human forensic investigations.