Non-invasive imaging biomarkers to assess nonalcoholic fatty liver disease: A review

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.

Non-invasive Scores and Serum Biomarkers for Fatty Liver in the Era of Metabolic Dysfunction-associated Steatotic Liver Disease (MASLD): A Comprehensive Review From NAFLD to MAFLD and MASLD

PURPOSE OF REVIEW

The prevalence of non-alcoholic fatty liver disease (NAFLD) is rapidly increasing worldwide, making it the leading cause of liver related morbidity and mortality. Currently, liver biopsy is the gold standard for assessing individuals with steatohepatitis and fibrosis. However, its invasiveness, sampling variability, and impracticality for large-scale screening has driven the search for non-invasive methods for early diagnosis and staging. In this review, we comprehensively summarise the evidence on the diagnostic performance and limitations of existing non-invasive serum biomarkers and scores in the diagnosis and evaluation of steatosis, steatohepatitis, and fibrosis.

RECENT FINDINGS

Several non-invasive serum biomarkers and scores have been developed over the last decade, although none has successfully been able to replace liver biopsy. The introduction of new NAFLD terminology, namely metabolic dysfunction-associated fatty liver disease (MAFLD) and more recently metabolic dysfunction-associated steatotic liver disease (MASLD), has initiated a debate on the interchangeability of these terminologies. Indeed, there is a need for more research on the variability of the performance of non-invasive serum biomarkers and scores across the diagnostic entities of NAFLD, MAFLD and MASLD. There remains a significant need for finding valid and reliable non-invasive methods for early diagnosis and assessment of steatohepatitis and fibrosis to facilitate prompt risk stratification and management to prevent disease progression and complications. Further exploration of the landscape of MASLD under the newly defined disease subtypes is warranted, with the need for more robust evidence to support the use of commonly used serum scores against the new MASLD criteria and validation of previously developed scores.

Associations Between Multiparametric US-Based Indicators and Pathological Status in Patients with Metabolic Associated Fatty Liver Disease

OBJECTIVE

Noninvasive evaluation of metabolic dysfunction-associated fatty liver disease (MAFLD) using ultrasonography holds significant clinical value. The associations between ultrasound (US)-based parameters and the pathological spectra remain unclear and controversial. This study aims to investigate the associations thoroughly.

METHODS

The participants with MAFLD undergoing liver biopsy and multiparametric ultrasonography were prospectively recruited from December 2020 to September 2022. Three US-based parameters, namely attenuation coefficient (AC), liver stiffness (LS) and dispersion slope (DS) were obtained. The relationship between these parameters and steatosis grades, inflammation grades and fibrosis stages was examined.

RESULTS

In this study with 116 participants, AC values significantly differed across distinct steatosis grades (p < 0.001), while DS and LS values varied among inflammation grades (p < 0.001) and fibrosis stages (p < 0.001). The area under the receiver operating characteristic curves (AUCs) of AC ranged from 0.82 to 0.84 for differentiating steatosis grades, while AUCs of LS ranged from 0.62 to 0.76 for distinguishing inflammation grades and 0.83-0.95 for discerning fibrosis stages. AUCs for DS ranged from 0.79 to 0.81 in discriminating inflammation grades and 0.80-0.88 for differentiating fibrosis stages. Subgroup analysis revealed that LS demonstrated different trends in inflammation grade but consistent trends in fibrosis stage across subgroups, whereas DS showed consistent trends for both inflammation grade and fibrosis stage across all subgroups.

CONCLUSION

AC values indicate the degree of hepatic steatosis but not inflammation or fibrosis. LS values are determined only by fibrosis stage and are not associated with inflammation grades. DS values are associated with both fibrosis and inflammation grades.

Comparison of magnetic resonance elastography and diffusion-weighted imaging for differentiating benign and malignant liver lesions

Background

Imaging is a crucial diagnostic tool in focal liver lesions (FLLs) diagnosis. Without the need for an intravenous contrast agent, two such MRI methods that can distinguish between benign and malignant FLLs are diffusion-weighted imaging (DWI) and magnetic resonance elastography (MRE). The purpose of this study was to assess the utility of diffusion-weighted magnetic resonance imaging and magnetic resonance elastography in the identification and differentiation of benign and malignant hepatic focal lesions.

Methods

This cross-sectional study was carried out on ninety patients (with mean age 52 years) with hepatic focal lesions (29 benign and 61 malignant). Both MRE and DWI were performed on the patients. A modified gradient-echo sequence was used for MRE, and respiratory-triggered fat-suppressed single-shot echoplanar DW imaging (b = 0.800) was used for DWI. Maps of the apparent diffusion coefficient (ADC) and stiffness were produced. Regions of interest were placed over the FLLs on stiffness and ADC maps to get FLL ADC values and mean stiffness. Receiver operating curve (ROC) analysis was used to compare the roles of MRE and DWI in the differentiation of benign and malignant FLL.

Results

The ADC of FLLs and MRE stiffness exhibited strong negative correlation [(r: −0.559; p < 0.001)]. Compared to malignant FLLs, benign FLLs had much higher mean ADC values. However, compared to benign FLLs, malignant FLLs exhibited much greater mean stiffness. FNH has the lowest mean stiffness of all FLLs, at less than 2.22 kPa. Among FLLs, CCAs had the lowest mean ADC values and the highest mean stiffness. The results showed that the MRE and DWI cutoff values were > 4.23 and ≤ 1.43, respectively; the area under the curve (AUC) values were 0.991 and 0.894, and the sensitivity and specificity results were 96.7%, 93.1%, and 85.2%, 89.7%, respectively.

Conclusions

MRE was found to be more sensitive method for identifying benign and malignant hepatic focal lesions than DWI.

Galectin-3 and Severity of Liver Fibrosis in Metabolic Dysfunction-Associated Fatty Liver Disease

Metabolic dysfunction-associated Fatty Liver Disease (MAFLD) is a chronic liver disease characterized by the accumulation of fat in the liver and hepatic steatosis, which can progress to critical conditions, including Metabolic dysfunction-associated Steatohepatitis (MASH), liver fibrosis, hepatic cirrhosis, and hepatocellular carcinoma. Galectin-3, a member of the galectin family of proteins, has been involved in cascades that are responsible for the pathogenesis and progression of liver fibrosis in MAFLD. This review summarizes the present understanding of the role of galectin-3 in the severity of MAFLD and its associated liver fibrosis. The article assesses the underlying role of galectin-3-mediated fibrogenesis, including the triggering of hepatic stellate cells, the regulation of extracellular degradation, and the modulation of immune reactions and responses. It also highlights the assessments of the potential diagnostic and therapeutic implications of galectin-3 in liver fibrosis during MAFLD. Overall, this review provides insights into the multifaceted interaction between galectin-3 and liver fibrosis in MAFLD, which could lead to the development of novel strategies for diagnosis and treatment of this prevalent liver disease.

Characterization of hepatic fatty acids using magnetic resonance spectroscopy for the assessment of treatment response to metformin in an eNOS-/- mouse model of metabolic nonalcoholic fatty liver disease/nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease worldwide. Liver biopsy remains the gold standard for diagnosis and staging of disease. There is a clinical need for noninvasive diagnostic tools for risk stratification, follow-up, and monitoring treatment response that are currently lacking, as well as preclinical models that recapitulate the etiology of the human condition. We have characterized the progression of NAFLD in eNOS^-/- mice fed a high fat diet (HFD) using noninvasive Dixon-based magnetic resonance imaging and single voxel STEAM spectroscopy-based protocols to measure liver fat fraction at 3 T. After 8 weeks of diet intervention, eNOS^-/- mice exhibited significant accumulation of intra-abdominal and liver fat compared with control mice. Liver fat fraction measured by ¹ H-MRS in vivo showed a good correlation with the NAFLD activity score measured by histology. Treatment of HFD-fed NOS3^-/- mice with metformin showed significantly reduced liver fat fraction and altered hepatic lipidomic profile compared with untreated mice. Our results show the potential of in vivo liver MRI and ¹ H-MRS to noninvasively diagnose and stage the progression of NAFLD and to monitor treatment response in an eNOS^-/- murine model that represents the classic NAFLD phenotype associated with metabolic syndrome.

Correlation between CT Abdominal Anthropometric Measurements and Liver Density in Individuals with Non-Alcoholic Fatty Liver Disease

Background: With a growing frequency, nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease worldwide. NAFLD has a strong correlation with other metabolic disorders, such as obesity, particularly abdominal obesity, even though the underlying causes or risk factors are not entirely understood. This study aims to investigate correlations between abdominal anthropometric measurements and the presence and intensity of liver steatosis as assessed by unenhanced computed tomography (CT). Methods: One hundred and nineteen patients (male/female, 66/53; mean age 54.54 +/− 12.90 years) underwent abdominal non–contrast-enhanced CT. CT images were examined to determine the attenuation of liver parenchyma, subcutaneous fat depth, and waist circumference (WC). Results: Among all patients, WC (r = −0.78, p < 0.0001), infraumbilical subcutaneous fat thicknesses (r = −0.51, p < 0.0001), right paraumbilical subcutaneous fat thicknesses (r = −0.62, p < 0.0001), and left paraumbilical subcutaneous fat thicknesses (r = −0.53, p < 0.0001) had a high inverse correlation with the liver attenuation values. The presence of T2D (OR: 2.40, p = 0.04), WC (OR: 11.45, p < 0.001), right paraumbilical (OR: 10.09, p < 0.001), left paraumbilical (OR: 2.81, p = 0.01), and infraumbilical (OR: 3.06, p = 0.007) were strongly independent predictors of NAFLD risk. Moreover, regarding the laboratory parameters, only the higher value of GGT (OR: 2.84, p = 0.009) is a predictor of NAFLD risk. Conclusions: Our data show that higher baseline values of all abdominal anthropometric measurements are correlated with liver attenuation and act as predictors of NAFLD risk.

Superb Microvascular Imaging-Based Vascular Index to Assess Adult Hepatic Steatosis: A Feasibility Study

The aim of the study was to assess the feasibility of using a superb microvascular imaging-based vascular index (SMI-VI) for evaluating adult hepatic steatosis. We prospectively compared liver parenchyma SMI-VI (color pixels/total pixels in the region of interest), portal vein velocity, hepatic artery Doppler parameters (peak systolic velocity, end diastolic velocity, resistive index) and serum lipid and alanine aminotransferase (ALT) levels between 16 normal livers and 34 steatotic livers using magnetic resonance imaging-proton density fat fraction (MRI-PDFF) as the reference. On the basis of a two-tailed t-test, differences in SMI-VI, portal vein velocity, MRI-PDFF and ALT between normal (MRI-PDFF <5%) and steatotic (MRI-PDFF ≥5%) livers were statistically significant (p < 0.02), whereas hepatic artery Doppler parameters and triglyceride levels were not (p > 0.05). We observed an inverse correlation of SMI-VI with MRI-PDFF (r = -0.88). With 0.19 as the best cutoff value, the area under the receiver operating characteristic curve, sensitivity and specificity of SMI-VI for determining ≥mild (MRI-PDFF ≥5%) non-alcoholic fatty liver disease (NAFLD) were 0.95, 96% and 94%, respectively. Our results indicate the feasibility of using SMI-VI to assess adult hepatic steatosis. SMI-VI is a potential surrogate marker in the screening for NAFLD.

Reliability of Performing Multiparametric Ultrasound in Adult Livers

PURPOSE

The aim of the study was to test inter-observer and intra-observer reliability of measuring multiparametric ultrasound in adult livers.

METHODS

We prospectively measured shear wave velocity (SWV, m/s), shear wave dispersion slope (SWD, m/s/kHz), attenuation coefficient (ATI, dB/cm/MHz), normalized local variance (NLV), and echo intensity ratio of liver to kidney (L/K ratio) in 21 adults who underwent liver magnetic resonance imaging-proton density fat fraction (MRI-PDFF). Intraclass correlation coefficient and 95% Bland-Altman limits of agreement (95% LOA) were used to analyze intra- and inter-observer reproducibility.

RESULTS

Based on liver MRI-PDFF, 21 participants (8 men and 13 women, mean age 55 years) were divided into group 1 (11 normal livers, MRI-PDFF <5%) and group 2 (10 steatotic livers, MRI-PDFF ≥5%). ICCs for intra-observer repeatability and inter-observer reproducibility in measuring multiple ultrasound parameters in both normal and steatotic livers were above 0.75. However, 95% confidence interval for measuring SWD in all livers and L/K ratio in normal livers was 0.38-0.90 and 0.47-0.91, respectively. Differences in SWV, SWD, ATI, NLV, L/K ratio, and MRI-PDFF between participants with and without hepatic steatosis were significant (p < .05), whereas serum biomarkers and body mass index were not (p > .05), based on a two-tailed t-test.

CONCLUSIONS

The results suggest that the repeatability and reproducibility for measuring liver SWV, ATI, and NLV are moderate to excellent, while those for SWD and L/K ratio are poor. Standardized machine settings, scanning protocols, and operator training are suggested in performing multiparametric ultrasound of the liver.