Use of magnetic resonance elastography to assess hepatic fibrosis in children with chronic liver disease

Designing Clinical Trials in Pediatric Nonalcoholic Steatohepatitis: Tips for Patient Selection and Appropriate Endpoints

Nonalcoholic fatty liver disease (NAFLD) is common in children and may progress to nonalcoholic steatohepatitis (NASH), advanced fibrosis, and even cirrhosis in childhood or early adulthood, indicating the need for pharmacologic treatment in this age group. Multiple trials are evaluating different therapeutic targets for NASH with fibrosis in adults, and the U.S. Food and Drug Administration has recently provided clear guidance to the pharmaceutical industry on developing drugs for the treatment of noncirrhotic NASH with liver fibrosis. Pediatric NAFLD has several unique aspects that distinguish it from the adult disease in terms of histology, our understanding of the natural history, and the utility of noninvasive tests. These differences have the potential to impact the design of clinical trials to test different drugs in the pediatric population. The aim of this article is to provide a review of common misconceptions regarding pediatric NAFLD and key differences from adult NAFLD. We have provided our recommendations on the design of early proof-of-concept and late phase 2 trials based on lessons learned from previous clinical trials. We believe that clinical drug development for children with NAFLD should happen in parallel with ongoing adult trials.

Assessment of liver T1 mapping in fontan patients and its correlation with magnetic resonance elastography-derived liver stiffness

OBJECTIVES

To explore the utility of liver T1 mapping in Fontan patients and its correlation to magnetic resonance elastography (MRE)-derived liver stiffness.

BACKGROUND AND AIMS

Liver disease is a major long-term extra cardiac complication in the Fontan population. MRE is frequently used to quantify liver stiffness in Fontan patients; however, it has certain limitations. Native T1 mapping by cardiac magnetic resonance (CMR) is useful in assessment of cardiac fibrosis, but its potential in evaluating liver fibrosis and its correlation to MRE-derived liver stiffness in Fontan patients have not been reported.

METHODS

Fontan patients who underwent CMR and MRE were included. Liver Native T1, extracellular volume (ECV) and delta coefficients were measured and correlated with MRE-derived liver stiffness in all Fontan patients. Native liver T1 in Fontan patients were compared to normal controls with biventricular circulation and no known liver disease.

RESULTS

A total of 17 Fontan patients and 7 normal controls were included in this study. Fontan patients had significantly higher liver native T1 (690 ± 41 ms vs 620 ± 35 ms; p < 0.001) as compared to controls. There was strong positive correlation between MRE derived liver stiffness and liver native T1 (r = 0.81, p < 0.001).

CONCLUSIONS

Liver native T1 was significantly elevated in Fontan patients compared to controls and strongly correlated with MRE-derived liver stiffness. This technique may prove to be a useful noninvasive imaging biomarker for assessing liver fibrosis in the Fontan population.

Pediatric NAFLD: an overview and recent developments in diagnostics and treatment

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in children and adults in industrialized countries. Besides liver-related morbidity, NAFLD is also associated with an increased risk of cardiovascular disease, type 2 diabetes and mortality at adult age. However, despite the high prevalence and serious complications, diagnosing and staging of disease remains complicated due to a lack of accurate screening tools and non-invasive methods to detect fibrosis. Areas covered: Recent insights in epidemiology, pathogenesis, diagnostic evaluation and treatment options in pediatric NAFLD are being reviewed, with a particular focus on new developments in diagnostic tools. Expert opinion: Due to their long life span, children with NAFLD are particularly at risk of complications in their lifetime. Therefore, an effective screening strategy for children to identify those with NAFLD at risk of complications is urgently needed. This is further underscored by new pharmacological therapies that are expected to become available in the next 5 years. Momentarily no accurate non-invasive method for diagnosing pediatric NAFLD is available. New promising biomarkers and imaging tools could hopefully provide better screening tools and could contribute to the development of a successful management plan to identify children with NAFLD.

Magnetic resonance elastography SE-EPI vs GRE sequences at 3T in a pediatric population with liver disease

PURPOSE

The goal of our study is to compare hepatic stiffness measures using gradient-recalled echo (GRE) versus spin-echo echo planar imaging (SE-EPI)-based MR Elastography (MRE) at 3T used to measure hepatic stiffness in a patients with suspected liver diseases.

MATERIALS AND METHODS

This retrospective study included 52 patients with liver disease who underwent a 3T MRE exam including both an investigational SE-EPI-based technique and a product GRE-based technique. Regions of interest (ROI) were placed on the elastograms to measure elastography-derived liver stiffness as well as the area included within the ROIs. The mean liver stiffness values and area of ROIs were compared.

RESULTS

The mean liver stiffness was 3.72 kilopascal (kPa) ± 1.29 using GRE MRE and 3.78 kPa ± 1.13 using SE-EPI MRE. Measurement of liver stiffness showed excellent agreement between the two pulse sequences with a mean bias of - 0.1 kPa (range - 1.8 to 1.7 kPa) between sequences. The mean measurable ROI area was higher with SE-EPI (313.8 cm² ± 213.8) than with the GRE technique (208.6 cm² ± 114.8), and the difference was statistically significant (P < 0.05).

CONCLUSIONS

Our data shows excellent agreement of measured liver stiffness between GRE and SE-EPI-based sequences at 3T. Our results show the advantage of a SE-EPI MRE sequence in terms of image quality, ROI size and acquisition time with equivalent liver stiffness measurements as compared to GRE-MRE sequence.

Diagnostic performance of quantitative magnetic resonance imaging biomarkers for predicting portal hypertension in children and young adults with autoimmune liver disease

BACKGROUND

Primary sclerosing cholangitis, autoimmune hepatitis and autoimmune sclerosing cholangitis are forms of chronic, progressive autoimmune liver disease (AILD) that can affect the pediatric population.

OBJECTIVE

To determine whether quantitative MRI- and laboratory-based biomarkers are associated with conventional imaging findings of portal hypertension (radiologic portal hypertension) in children and young adults with AILD.

MATERIALS AND METHODS

Forty-four patients with AILD enrolled in an institutional registry underwent a research abdominal MRI examination at 1.5 tesla (T). Five quantitative MRI techniques were performed: liver MR elastography, spleen MR elastography, liver iron-corrected T1 mapping, liver T2 mapping, and liver diffusion-weighted imaging (DWI, quantified as apparent diffusion coefficients). Two anatomical sequences were used to document splenomegaly, varices and ascites. We calculated aspartate aminotransferase (AST)-to-platelet ratio index (APRI) and fibrosis-4 (FIB-4) scores - laboratory-based biomarkers of liver fibrosis. We used receiver operating characteristic (ROC) curve analyses to establish the diagnostic performance of quantitative MRI and laboratory biomarkers for indicating the presence of radiologic portal hypertension.

RESULTS

Twenty-three (52%) patients were male; mean age was 15.2±4.0 years. Thirteen (30%) patients had radiologic portal hypertension. Liver and spleen stiffness demonstrated the greatest diagnostic performance for indicating the presence of portal hypertension (area-under-the-ROC-curve [AUROC]=0.98 and 0.96, respectively). The APRI and FIB-4 scores also demonstrated good diagnostic performance (AUROC=0.87 and 0.88, respectively).

CONCLUSION

MRI-derived measures of liver and spleen stiffness as well as laboratory-based APRI and FIB-4 scores are highly associated with imaging findings of portal hypertension in children and young adults with AILD and thus might be useful for predicting portal hypertension impending onset and directing personalized patient management.

Understanding susceptibility and targeting treatment in non-alcoholic fatty liver disease in children; moving the fulcrum

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of paediatric liver disease, affecting 10% of school-aged children and 44–70% of obese children and young people (CYP) in the western world. Encompassing a spectrum from simple steatosis to steatohepatitis and progressive fibrosis, the disease is rapidly becoming the most common indication for liver transplantation. The molecular pathogenesis of NAFLD remains only partially understood. Development and progression of NAFLD is influenced by genetic and nutritional factors, insulin resistance, oxidative stress, gut microbiome, bile acid metabolism and lipid/glucose handling and is closely associated with overweight and obesity. Lifestyle change is the only proven effective treatment for paediatric NAFLD, however this is difficult to achieve in many. Given that moderate or severe fibrosis is already present in 30–50% of children with NAFLD at the time of presentation, progression in CYP may be more rapid, though adequate outcome data do not yet exist in this cohort. CYP with NAFLD are an excellent population in which to study underlying mechanisms and interventions to correct disease progression as they are largely unaffected by other environmental influences such as alcohol and may represent the more severe end of the spectrum in terms of early onset. Undoubtedly genetic and epigenetic mechanisms determine a large proportion of susceptibility to the disease and potentially, identification of individuals at risk may allow for targeted therapy. This review with give a clinical perspective of paediatric NAFLD focused on identifying those at risk of progressive disease and what to consider in attempting to modify risk.

Predicting gastroesophageal varices through spleen magnetic resonance elastography in pediatric liver fibrosis

BACKGROUND

A recent retrospective study confirmed that hepatic stiffness and splenic stiffness measured with magnetic resonance elastography (MRE) are strongly associated with the presence of esophageal varices. In addition, strong correlations have been reported between splenic stiffness values measured with MRE and hepatic venous pressure gradients in animal models. However, most studies have been conducted on adult populations, and previous pediatric MRE studies have only demonstrated the feasibility of MRE in pediatric populations, while the actual clinical application of spleen MRE has been limited.

AIM

To assess the utility of splenic stiffness measurements by MRE to predict gastroesophageal varices in children.

METHODS

We retrospectively reviewed abdominal MRE images taken on a 3T system in pediatric patients. Patients who had undergone Kasai operations for biliary atresia were selected for the Kasai group, and patients with normal livers and spleens were selected for the control group. Two-dimensional spin-echo echo-planar MRE acquisition centered on the liver, with a pneumatic driver at 60 Hz and a low amplitude, was performed to obtain hepatic and splenic stiffness values. Laboratory results for aspartate aminotransferase to platelet ratio index (APRI) were evaluated within six months of MRE, and the normalized spleen size ratio was determined with the upper normal size limit. All Kasai group patients underwent gastroesophageal endoscopy during routine follow-up. The Mann-Whitney U test, Kendall's tau b correlation and diagnostic performance analysis using the area under the curve (AUC) were performed for statistical analysis.

RESULTS

The median spleen MRE value was 5.5 kPa in the control group (n = 9, age 9-18 years, range 4.7-6.4 kPa) and 8.6 kPa in the Kasai group (n = 22, age 4-18 years, range 5.0-17.8 kPa). In the Kasai group, the APRI, spleen size ratio and spleen MRE values were higher in patients with portal hypertension (n = 11) than in patients without (n = 11) (all P < 0.001) and in patients with gastroesophageal varices (n = 6) than in patients without (n = 16) (all P < 0.05), even though their liver MRE values were not different. The APRI (τ = 0.477, P = 0.007), spleen size ratio (τ = 0.401, P = 0.024) and spleen MRE values (τ = 0.426, P = 0.016) also correlated with varices grades. The AUC in predicting gastroesophageal varices was 0.844 at a cut-off of 0.65 (100% sensitivity and 75% specificity) for the APRI, and 0.844 at a cut-off of 9.9 kPa (83.3% sensitivity and 81.3% specificity) for spleen MRE values.

CONCLUSION

At a cut-off of 9.9 kPa, spleen MRE values predicted gastroesophageal varices as well as the APRI and spleen size ratio in biliary atresia patients after the Kasai operation. However, liver MRE values were not useful for this purpose.

Can MR elastography be used to measure liver stiffness in patients with iron overload?

Untreated hepatic iron overload causes hepatic fibrosis and cirrhosis and can predispose to hepatocellular carcinoma. MR elastography (MRE) provides a non-invasive means to measure liver stiffness, which correlates with liver fibrosis but standard gradient recalled echo (GRE)-based MRE techniques fail in patients with high iron due to very low hepatic signal. Short echo time (TE) 2D spin echo echoplanar imaging (SE-EPI)-based MRE may allow measurement of stiffness in the iron loaded liver. The purpose of this study was to describe the use of such an MRE sequence in patients undergoing liver iron quantification by MRI. In our preliminary study of 43 patients with mean LIC of 9.3 mg/g (range 1.8-21.5 mg/g), liver stiffness measurements could be made in 77% (33/43) of patients with a short TE, SE-EPI based MRE sequence. On average, mean LIC in patients with failed MRE was higher than in those with successful MRE (15.9 mg/g dry weight vs. 7.3 mg/g), but a cut-off value for successful MRE could not be established. Seven patients (21% of those with successful MRE) had liver stiffness values suggestive of the presence of significant fibrosis (> 2.49 kPa). A short TE, SE-EPI based MR elastography sequence allows successful measurement of liver stiffness in a majority of patients with liver iron loading, potentially allowing non-invasive screening for fibrosis.

Using T1 mapping in cardiovascular magnetic resonance to assess congestive hepatopathy

The goal of this study was to assess the ability of quantitative T1 cardiovascular magnetic resonance (CMR) imaging to calculate liver extracellular volume (ECV) in patients with varying degrees of congestive hepatopathy (CH). T1 measurements and ECV calculations were performed retrospectively in three cohorts of patients: normal cardiac function, tetralogy of fallot (TOF) repair and Fontan palliation. All CMR studies included modified look-locker inversion recovery (MOLLI) T1 mapping scans performed pre- and post-injection of a gadolinium-based contrast agent (GBCA). Pixel intensity data were manually collected from images of the liver and cardiac blood pool to determine contrast-induced changes in T1 for liver and blood. These data were then used to compute liver ECV. 172 subjects were included in the study. Of these, 140 subjects were normal cardiac function patients, 16 were TOF repair patients and 16 patients were with Fontan palliation. A statistically significant difference in both the liver native T1 and ECV measurements was found between patients with normal cardiac function vs. Fontan palliation patients (p < 0.01). Our data indicate that measuring T1 maps both pre- and post-GBCA injection within CMR scan session can be used to follow progression of liver fibrosis. This technique has the potential to improve diagnosis and treatment of patients with chronic liver disease and liver fibrosis.

Magnetic resonance elastography of liver and spleen: Methods and applications

The viscoelastic properties of the liver and spleen can be assessed with magnetic resonance elastography (MRE). Several actuators, MRI acquisition sequences and reconstruction algorithms have been proposed for this purpose. Reproducible results are obtained, especially when the examination is performed in standard conditions with the patient fasting. Accurate staging of liver fibrosis can be obtained by measuring liver stiffness or elasticity with MRE. Moreover, emerging evidence shows that assessing the tissue viscous parameters with MRE is useful for characterizing liver inflammation, non-alcoholic steatohepatitis, hepatic congestion, portal hypertension, and hepatic tumors. Further advances such as multifrequency acquisitions and compression-sensitive MRE may provide novel quantitative markers of hepatic and splenic mechanical properties that may improve the diagnosis of hepatic and splenic diseases.

Stiffness reconstruction methods for MR elastography

Assessment of tissue stiffness is desirable for clinicians and researchers, as it is well established that pathophysiological mechanisms often alter the structural properties of tissue. Magnetic resonance elastography (MRE) provides an avenue for measuring tissue stiffness and has a long history of clinical application, including staging liver fibrosis and stratifying breast cancer malignancy. A vital component of MRE consists of the reconstruction algorithms used to derive stiffness from wave-motion images by solving inverse problems. A large range of reconstruction methods have been presented in the literature, with differing computational expense, required user input, underlying physical assumptions, and techniques for numerical evaluation. These differences, in turn, have led to varying accuracy, robustness, and ease of use. While most reconstruction techniques have been validated against in silico or in vitro phantoms, performance with real data is often more challenging, stressing the robustness and assumptions of these algorithms. This article reviews many current MRE reconstruction methods and discusses the aforementioned differences. The material assumptions underlying the methods are developed and various approaches for noise reduction, regularization, and numerical discretization are discussed. Reconstruction methods are categorized by inversion type, underlying assumptions, and their use in human and animal studies. Future directions, such as alternative material assumptions, are also discussed.

Assessment of Nonalcoholic Fatty Liver Disease Progression in Children Using Magnetic Resonance Imaging

OBJECTIVE

To assess liver disease progression using paired magnetic resonance imaging (MRI) measurements of liver fat fraction (FF) and stiffness.

STUDY DESIGN

Retrospective cohort study including patients with nonalcoholic fatty liver disease who had undergone repeat MRI studies. Descriptive statistics were used, as well as Pearson or Spearman correlation when appropriate. Mixed model analyses were used to determine relationships between liver FF/stiffness and predictor variables.

RESULTS

Sixty-five patients (80% non-Hispanic, mean age 14 ± 3 years) were included. Time from first to last MRI was 27 ± 14 months. Over time, body mass index z score remained stable, and there were no significant differences in mean serum aminotransferases, insulin, glucose, triglycerides, low-density lipoprotein, and high-density lipoprotein (HDL) levels. However, the proportion of patients with alanine aminotransferase (ALT) < 50 U/L increased. MRI FF and stiffness decreased in 29% and 20% of patients, respectively, and increased in 25% and 22% of patients, respectively. There was a weak positive correlation between FF change and ALT change (r = 0.41, P = .053) and a moderate negative correlation between change in FF and change in serum HDL levels (r = -0.58, P = .004). After adjusting for HDL, increase in serum insulin was the only variable predictive of increase in FF (P = .061). There was no correlation between change in liver stiffness and change in ALT (r = .02, P = .910).

CONCLUSIONS

MRI-determined hepatic FF and stiffness improved in a minority of patients overtime. ALT levels were not reflective of the change in FF or stiffness. MRI-based imaging is complementary in the assessment of NAFLD progression.

Putting it all together: established and emerging MRI techniques for detecting and measuring liver fibrosis

Chronic injury to the liver leads to inflammation and hepatocyte necrosis, which when untreated can lead to myofibroblast activation and fibrogenesis with deposition of fibrous tissue. Over time, liver fibrosis can accumulate and lead to cirrhosis and end-stage liver disease with associated portal hypertension and liver failure. Detection and accurate measurement of the severity of liver fibrosis are important for assessing disease severity and progression, directing patient management, and establishing prognosis. Liver biopsy, generally considered the clinical standard of reference for detecting and measuring liver fibrosis, is invasive and has limitations, including sampling error, relatively high cost, and possible complications. For these reasons, liver biopsy is suboptimal for fibrosis screening, longitudinal monitoring, and assessing therapeutic efficacy. A variety of established and emerging qualitative and quantitative noninvasive MRI methods for detecting and staging liver fibrosis might ultimately serve these purposes. In this article, we review multiple MRI methods for detecting and measuring liver fibrosis and discuss the diagnostic performance and specific strengths and limitations of the various techniques.

Hepatitis C virus infection in children in the era of direct-acting antiviral

Hepatitis C virus (HCV) infection remains an important global health problem with chronic infection affecting approximately 11 million children worldwide. The emergence of direct-acting antiviral (DAA) therapies and the development of non-invasive methods for the determination of liver fibrosis will significantly improve the management of paediatric patients with chronic HCV infection in subsequent years. For paediatric patients, a new era of highly effective DAA agents is beginning, and the first results of available clinical trials are very promising. In this era, the identification and monitoring of patients continues to be an important issue. The availability of non-invasive serological and imaging methods to measure hepatic fibrosis enables the identification of patients with significant or advanced liver fibrosis stages. This article summarizes the current data on the epidemiology and progress of research aimed to evaluate the new therapies and non-invasive methods for liver injury in paediatric patients with chronic hepatitis C.

The search for noninvasive methods to identify liver fibrosis in children with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the obesity epidemic. Recent studies have clearly shown that the stage of fibrosis in adults with NAFLD is the most important histological feature in long-term outcomes and the development of liver-related complications. Despite the paucity of data regarding the natural history of pediatric NAFLD, its progression to cirrhosis and end-stage liver disease requiring liver transplantation is well documented. Given the high prevalence of NAFLD in children and adults, there is an urgent need to find safe and cost-effective alternatives to biopsy to determine the stage of liver fibrosis. In this review, we provide a concise overview of different noninvasive methods for diagnosing and staging liver fibrosis in children with NAFLD.

Assessment of Liver Disease Progression in Cystic Fibrosis Using Transient Elastography

OBJECTIVES

Cystic fibrosis-related liver disease (CFLD) can develop silently in early life and approximately 10% of children with cystic fibrosis (CF) become cirrhotic before adulthood. Clinical, biological, and ultrasound criteria used to define CFLD often reveal liver involvement at an advanced stage. The aim of this retrospective study was to assess the progression of liver stiffness measurement (LSM) in pediatric patients with CF.

METHODS

The change of LSM, expressed as kPa/year and %/year, was measured using transient elastography (Fibroscan) in 82 children with CF (median age: 6.8 years, interquartile range [IQR]: 5.8). Mean time interval between the 2 LSM was 3.5 years.

RESULTS

Median initial liver stiffness was 3.7 kPa (IQR: 1.3), and then progressed by 0.23 kPa/year, that is, 6%/year. The 7 patients who developed CFLD had a higher initial level of alanine aminotransferase (50 [IQR: 15] vs 30 [IQR: 18], P = 0.0001) and presented a more rapid progression of LSM (0.94 vs 0.23 kPa/year, P = 0.02).

CONCLUSIONS

The present study shows that the slope of worsening of liver stiffness is greater in patients who will develop CFLD, suggesting that annual transient elastography may be useful to detect risk of severe liver disease at an earlier stage.

Correlating liver stiffness with disease severity scoring system (DS3) values in Gaucher disease type 1 (GD1) patients

Gaucher disease (GD) is an autosomal-recessive lysosomal storage disease caused by a deficiency of the enzyme, glucocerebrocidase, resulting in accumulation of lipid-laden storage cells in multiple organs such as bone marrow, liver, spleen, and lungs. Type 1 Gaucher disease is the most common form of this condition in which the brain and spinal cord (the central nervous system) are not affected. The Gaucher disease severity scoring system (GD-DS3) is typically used to assess disease severity accounting for skeletal, hematologic, and visceral disease. In addition to being time consuming for the clinician to calculate the scores, some of the assessments are subjective and may falsely increase or decrease disease severity. The purpose of this study was to determine if there is a correlation between liver stiffness values obtained from MR elastography (MRE) and the GD-DS3 score. An IRB approved, HIPAA compliant retrospective study was performed. All patients with type 1 GD imaged with MRE between 2011 and 2016 were included in this study. Clinical and imaging data was collected. Two pediatric radiologists analyzed MR images from abdomen and thigh studies independently to determine bone marrow involvement using a semi-quantitative scoring system with one reviewer analyzing a subset of studies to determine inter-observer reliability. The collected data was used to calculate a GD-DS3 score for all patients. GD-DS3 scores were compared with liver MRE stiffness values. Clinical MRE scores were plotted against GD-DS3 severity scores for 31 patients (15 males, 16 females; median age 27years, age range: 4-67years). The median GD-DS3 score was 4 (range: 1-10.1) and median MRE value was 2.43kPa (range: 1.30-5.20kPa). A significant positive correlation was found between MRE and GD-DS3 scores; Pearson's correlation coefficient value of r=0.47, p<0.001 for all scores, r=0.68, p<0.001 for complete scores and r=0.46, p<0.07 for incomplete scores. The inter-observer variation of bone marrow burden showed only fair agreement with a Kappa coefficient of 0.26. There is a significant positive correlation between increasing liver stiffness and increasing composite GD-DS3 scores. This supports the use of MRE, a non-invasive reproducible quantitative test, as both an additional assessment and independent marker for monitoring disease severity and progression in GD.

Diagnostic Performance of MR Elastography for Liver Fibrosis in Children and Young Adults with a Spectrum of Liver Diseases

Purpose To assess the diagnostic performance of magnetic resonance (MR) elastography-derived liver stiffness to detect liver fibrosis in a pediatric and young adult population with a spectrum of liver diseases. Materials and Methods This retrospective study included patients younger than 21 years of age who underwent MR elastography and liver biopsy within 3 months of one another between January 2012 and September 2016 for indications other than liver transplantation or Fontan palliation of congenital heart disease. MR elastography examinations were reprocessed by a single observer, blinded to pathologic findings. Pathology specimens were reviewed by a single pathologist who scored steatosis (lipid in ≥ 5% of hepatocytes) and staged fibrosis. Receiver operating characteristic (ROC) curves were used to assess diagnostic performance. Results A total of 86 patients, 49 (57%) male with a median age of 14.2 years (range, 0.3-20.6 years), were included. Fifty-one patients (59.3%) had Ludwig stage 2 or higher fibrosis; 44 patients (51.2%) had hepatic steatosis. The area under the ROC curve for Ludwig stage 0-1 versus stage 2 or higher fibrosis was 0.70 (95% confidence interval [CI]: 0.59, 0.81) for the whole population and was significantly lower for patients with steatosis versus those without (0.53 [95% CI: 0.35, 0.71] vs 0.82 [95% CI: 0.67, 0.96], P = .014). Optimal stiffness cut-offs for the entire population were 2.27 kPa with 68.6% sensitivity (95% CI: 57.2%, 80.1%) and 74.3% specificity (95% CI: 63.5%, 85.1%) or 1.67 kPa with 35.3% sensitivity (95% CI: 23.5%, 47.1%) and 91.4% specificity (95% CI: 84.5%, 98.3%). Conclusion In children and young adults, MR elastography performs significantly better for distinguishing stage 0-1 versus stage 2 or higher fibrosis in patients without steatosis than in those with steatosis. This suggests a confounding effect of steatosis or inflammation in the population with nonalcoholic fatty liver disease. ^© RSNA, 2018.

Magnetic resonance elastography measured shear stiffness as a biomarker of fibrosis in pediatric nonalcoholic fatty liver disease

Magnetic resonance elastography (MRE) is a promising technique for noninvasive assessment of fibrosis, a major determinant of outcome in nonalcoholic fatty liver disease (NAFLD). However, data in children are limited. The purpose of this study was to determine the accuracy of MRE for the detection of fibrosis and advanced fibrosis in children with NAFLD and to assess agreement between manual and novel automated reading methods. We performed a prospective, multicenter study of two-dimensional (2D) MRE in children with NAFLD. MR elastograms were analyzed manually at two reading centers, and using a new automated technique. Analysis using each approach was done independently. Correlations were determined between MRE analysis methods and fibrosis stage. Thresholds for classifying the presence of fibrosis and of advanced fibrosis were computed and cross-validated. In 90 children with a mean age of 13.1 ± 2.4 years, median hepatic stiffness was 2.35 kPa. Stiffness values derived by each reading center were strongly correlated with each other (r = 0.83). All three analyses were significantly correlated with fibrosis stage (center 1, ρ = 0.53; center 2, ρ = 0.55; and automated analysis, ρ = 0.52; P < 0.001). Overall cross-validated accuracy for detecting any fibrosis was 72.2% for all methods (95% confidence interval [CI], 61.8%-81.1%). Overall cross-validated accuracy for assessing advanced fibrosis was 88.9% (95% CI, 80.5%-94.5%) for center 1, 90.0% (95% CI, 81.9%-95.3%) for center 2, and 86.7% (95% CI, 77.9%-92.9%) for automated analysis.

CONCLUSION

2D MRE can estimate hepatic stiffness in children with NAFLD. Further refinement and validation of automated analysis techniques will be an important step in standardizing MRE. How to best integrate MRE into clinical protocols for the assessment of NAFLD in children will require prospective evaluation. (Hepatology 2017;66:1474-1485).

Quantitative Liver MRI-Biopsy Correlation in Pediatric and Young Adult Patients With Nonalcoholic Fatty Liver Disease: Can One Be Used to Predict the Other?

OBJECTIVE

The purpose of this study is to determine the relationships between quantitative liver MRI measurements and liver biopsy findings in pediatric and young adult patients with nonalcoholic fatty liver disease (NAFLD).

MATERIALS AND METHODS

Data were obtained from a registry that prospectively enrolls pediatric and young adult patients with biopsy-confirmed NAFLD at our tertiary medical center with parent or guardian and subject informed consent, as appropriate. Patients enrolled between November 2007 and June 2016 with a quantitative liver MRI examination within 6 months of biopsy were included (n = 69). Liver stiffness (kilopascals), volume (milliliters), and fat fraction (percentage) were extracted from MRI records. Multiple linear regression was used to determine the relationships between NAFLD activity score and quantitative MRI measures, and between MRI liver stiffness and histopathologic scores (steatosis, lobular inflammation, portal inflammation, hepatocyte ballooning, and fibrosis). Histopathologic data were extracted from medical records, with severity graded by hepatopathologists using Non-alcoholic Steatohepatitis (NASH) Clinical Research Network criteria. Ordinal logistic regression was used to assess the relationship between categoric NAFLD severity (simple steatosis vs NASH vs NASH with significant fibrosis) and MRI measures.

RESULTS

The mean (± SD) patient age at the time of MRI was 14.3 ± 2.8 years (range, 8-21 years); 25 (36.2%) patients were female. Liver biopsy was performed within a mean of 64.4 days of the MRI examination. There was a positive correlation between histopathologic steatosis and MRI liver fat fraction (ρ = 0.57; p < 0.0001). MRI fat fraction was the only significant imaging predictor of NAFLD activity score (p = 0.017). Fibrosis score was the only significant histopathologic predictor of MRI liver stiffness (p = 0.001). MRI liver volume was the only imaging predictor of categoric NAFLD severity (odds ratio = 1.001; 95% CI, 1.000-1.002; p = 0.007).

CONCLUSION

There was significant positive correlation between histopathologic and MRI liver fat measurements in our cohort. MRI liver stiffness did not predict the severity of fatty liver disease in children and young adults.

Management of Pediatric Nonalcoholic Fatty Liver Disease by Academic Hepatologists in Canada: A Nationwide Survey

BACKGROUND

The literature on the optimal clinical management of pediatric patients with nonalcoholic fatty liver disease (NAFLD) is limited. The objective of this study was to identify discrepancies in the care provided to patients with NAFLD by hepatologists practicing in academic centers across Canada.

METHODS

A nationwide survey was distributed electronically to all pediatric hepatologists practicing in university-affiliated hospitals using the infrastructure of the Canadian Pediatric Hepatology Research Group. The responses were anonymous.

RESULTS

The response rate to the survey was 79%. Everyone reported diagnosing NAFLD based on a combination of elevated transaminases and imaging suggestive of steatosis in the context of an otherwise negative workup for other liver diseases. Only 14% use liver biopsy to confirm the diagnosis. There are significant discrepancies in the frequency of screening for other comorbidities (eg, hypertension, sleep apnea, etc) and in the frequency of laboratory investigations (eg, lipid profile, transaminases, international normalized ratio, etc). Frequency of outpatient clinic follow-up varies significantly. Treatment is consistently based on lifestyle modifications; however, reported patient outcomes in terms of body mass index improvements are poor.

CONCLUSIONS

There are significant discrepancies in the care provided to children with NAFLD by hepatologists practicing in academic centers across Canada.

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.

MR elastography: high rate of technical success in pediatric and young adult patients

BACKGROUND

Magnetic resonance (MR) elastography allows the noninvasive assessment of liver stiffness, which is a surrogate for fibrosis.

OBJECTIVE

The purpose of this study was to describe our experience using liver MR elastography in a large pediatric population with attention to the frequency and causes of exam failure.

MATERIALS AND METHODS

Imaging records were searched for patients ≤18 years of age who underwent 2-D gradient recalled echo (GRE) MR elastography of the liver between September 2011 and August 2015 on one of two 1.5-T MRI platforms. Imaging reports and clinical records were reviewed for failed MR elastography acquisitions, factor(s) resulting in failure and whether a subsequent successful examination had been performed.

RESULTS

Four hundred sixty-eight MR elastography examinations were performed in 372 patients between 1.5 months and 18 years of age during the study period. Ninety-six percent (450/468) of the examinations were successful. There was no significant difference in mean age (12.6±3.6 vs. 11.2±4.1 years, P=0.12) or body mass index (BMI) (28.2±12.4 vs. 29.5±10 kg/m², P=0.6) between patients with and without successful examinations. MR elastography failures were due to poor paddle positioning resulting in inadequate generation of hepatic shear waves (n=5), iron overload (n=4), patient inability to tolerate MRI (n=3), patient breathing/motion (n=3), artifact from implanted hardware (n=1) and technical malfunction (n=2). Seven of nine (78%) repeat examinations were successful (78%).

CONCLUSION

Hepatic 2-D GRE MR elastography at 1.5 T is technically robust in children. Exam failure is infrequent and largely reflects patient specific factors, some of which can be mitigated with careful technique.

Repeatability of MR Elastography of Liver: A Meta-Analysis

Purpose To perform a meta-analysis to generate an estimate of the repeatability coefficient (RC) for magnetic resonance (MR) elastography of the liver. Materials and Methods A systematic search of databases was performed for publications on MR elastography during the 10-year period between 2006 and 2015. The identified studies were screened independently and were verified reciprocally by all authors. Two reviewers independently determined the percentage RC and effective sample size from each article. A forest plot was constructed of the percentage RC estimates from the 12 studies. Bootstrap 95% confidence intervals (CIs) were constructed for the summary percentage RCs. Results Twelve studies comprising 274 patients met the eligibility criteria and were included for analysis. A flow diagram of studies included according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was prepared for the inclusion and exclusion criteria. All studies included in the meta-analysis fulfilled four or more of the seven categories of the Quality Assessment of Diagnostic Accuracy Studies (QUADAS)-2. The estimated summary RC was 22% (95% CI: 16.1%, 28.2%). The three main sources for this heterogeneity were the trained versus untrained operator drawing contours to choose regions of interest, the time between two replicate examinations, and, finally, the field strength of the MR imaging unit. The RC estimates tended to be higher for studies that did not use a well-trained operator, those with 1.5-T field strength imaging units, and those with longer time intervals between examinations. Conclusion The meta-analysis results provide the basis for the following draft longitudinal Quantitative Imaging Biomarkers Alliance MR elastography claim: A measured change in hepatic stiffness of 22% or greater, at the same site and with use of the same equipment and acquisition sequence, indicates that a true change in stiffness has occurred with 95% confidence. ^© RSNA, 2017.

Limitations and opportunities of non-invasive liver stiffness measurement in children

Changes in liver structure are an important issue in chronic hepatopathies. Until the end of the 20^th century, these changes could only be determined by histological analyses of a liver specimen obtained via biopsy. The well-known limitations of this technique (i.e., pain, bleeding and the need for sedation) have precluded its routine use in follow-up of patients with liver diseases. However, the introduction of non-invasive technologies, such as ultrasound and magnetic resonance imaging, for measurement of liver stiffness as an indirect marker of fibroses has changed this situation. Today, several non-invasive tools are available to physicians to estimate the degree of liver fibrosis by analysing liver stiffness. This review describes the currently available tools for liver stiffness determination that are applicable to follow-up of liver fibrosis/cirrhosis with established clinical use in children, and discusses their features in comparison to the “historical” tools.

Proton Density Fat Fraction Measurements at 1.5- and 3-T Hepatic MR Imaging: Same-Day Agreement among Readers and across Two Imager Manufacturers

Purpose To determine the agreement of proton density fat fraction (PDFF) measurements obtained with hepatic magnetic resonance (MR) imaging among readers, imager manufacturers, and field strengths. Materials and Methods This HIPAA-compliant study was approved by the institutional review board. After providing informed consent, 24 adult volunteers underwent imaging with one 1.5-T MR unit (Ingenia; Philips Healthcare, Best, the Netherlands) and two different 3.0-T units (750 W [GE Healthcare, Waukesha, Wis] and Ingenia) on the same day to estimate hepatic PDFF. A single-breath-hold multipoint Dixon-based acquisition was performed with commercially available pulse sequences provided by the MR imager manufacturers (mDIXON Quant [Philips Healthcare], IDEAL IQ [GE Healthcare]). Five readers placed one large region of interest, inclusive of as much liver parenchyma as possible in the right lobe while avoiding large vessels, on imager-generated parametric maps to measure hepatic PDFF. Two-way single-measure intraclass correlation coefficients (ICCs) were used to assess interreader agreement and agreement across the three imaging platforms. Results Excellent interreader agreement for hepatic PDFF measurements was obtained with mDIXON Quant and the Philips 1.5-T unit (ICC, 0.995; 95% confidence interval [CI]: 0.991, 0.998), mDIXON Quant and the Philips 3.0-T unit (ICC, 0.992; 95% CI: 0.986, 0.996), and IDEAL IQ and the GE 3.0-T unit (ICC, 0.966; 95% CI: 0.939, 0.984). Individual reader ICCs for hepatic PDFF measurements across all three imager manufacturer-field strength combinations also showed excellent interimager agreement, ranging from 0.914 to 0.954. Conclusion Estimation of PDFF with hepatic MR imaging by using multipoint Dixon techniques is highly reproducible across readers, field strengths, and imaging platforms. ^© RSNA, 2017.

Liver transplantation for nonalcoholic steatohepatitis in young patients

Nonalcoholic steatohepatitis (NASH) is the hepatic manifestation of obesity and insulin resistance. The aim of this study was to determine the frequency of NASH as an indication for liver transplantation (LT) in children and young adults and to characterize patient and graft survival. The study included all children and young adult patients (up to the age of 40 years) who underwent LT in the United States for NASH cirrhosis from the 1987 to 2012 United Network for Organ Sharing (UNOS) database. Kaplan-Meier analysis was used to assess patient and graft survival. A total of 330 patients were included, 68% were Caucasian, and the mean BMI was 33.6 ± 6.3. Age at time of LT ranged between 4 and 40 years (mean 33.9 ± 6.6 years). Fourteen subjects were <18 years of age at time of LT and 20 were between the ages of 18 and 25 years. Median follow-up after 1st LT was 45.8 months [10.7, 97.3]. During this time, 30% of subjects (n = 100) died and 11.5% (n = 38) were retransplanted including 13 for NASH recurrence. In conclusion, NASH can progress to end-stage liver disease requiring LT in childhood and early adulthood. A significant number of young patients transplanted for NASH cirrhosis required retransplantation.

NASPGHAN Clinical Practice Guideline for the Diagnosis and Treatment of Nonalcoholic Fatty Liver Disease in Children: Recommendations from the Expert Committee on NAFLD (ECON) and the North American Society of Pediatric Gastroenterology, Hepatology and Nutrition (NASPGHAN)

Nonalcoholic fatty liver disease (NAFLD) is a highly prevalent chronic liver disease that occurs in the setting of insulin resistance and increased adiposity. It has rapidly evolved into the most common liver disease seen in the pediatric population and is a management challenge for general pediatric practitioners, subspecialists, and for health systems. In this guideline, the expert committee on NAFLD reviewed and summarized the available literature, formulating recommendations to guide screening and clinical care of children with NAFLD.

Pediatric Non-alcoholic Fatty Liver Disease

Childhood obesity has reached epidemic proportions, and by 2012, more than one third of American children were overweight or obese. As a result, increasingly, children are developing complications of obesity including liver disease. In fact, non-alcoholic fatty liver disease is the most common form of chronic liver disease seen in children today. Recently, there has been a burgeoning literature examining the pathogenesis, genetic markers, and role of the microbiome in this disease. On the clinical front, new modalities of diagnosing hepatic steatosis and hepatic fibrosis are being developed to provide non-invasive methods of surveillance in children. Lastly, the mainstay of treatment of pediatric non-alcoholic fatty liver disease (NAFLD) has been largely through lifestyle interventions, namely, dieting and exercise. Currently, there are a number of clinical trials examining novel lifestyle and drug therapies for NAFLD that are registered with the US National Institutes of Health ClinicalTrials.gov website.

Late graft hepatitis and fibrosis in pediatric liver allograft recipients: Current concepts and future developments

Liver transplantation (LT) in children now has a 20-year survival of >80%, but the longterm outcome of these grafts remains uncertain. Serial protocol liver biopsies after transplantation from several pediatric centres have demonstrated the gradual development of unexplained graft inflammation ("idiopathic" posttransplant hepatitis; IPTH) and graft fibrosis in biopsies obtained >12 months post-LT in children with good graft function and (near) normal liver biochemistry. Although the clinical significance of these findings is uncertain, there is evidence to suggest that IPTH may be a form of rejection or chronic antibody-mediated rejection as it is associated with the presence of auto/alloantibodies; de novo Class II donor-specific HLA antibodies (DSA); previous episodes of rejection, and may improve or be prevented with increased immunosuppression. Currently, the only method of diagnosing either hepatitis or fibrosis has been by serial protocol biopsies as neither serum markers of fibrosis nor noninvasive methods to detect fibrosis such as transient elastography (TE) are sufficiently validated in children. This review will focus on the diagnosis and management of idiopathic posttransplant hepatitis and graft fibrosis, discuss current methods for detecting graft injury, and potential mechanisms for their development. Liver Transplantation 22 1593-1602 2016 AASLD.

Prospective Assessment of Correlation between US Acoustic Radiation Force Impulse and MR Elastography in a Pediatric Population: Dispersion of US Shear-Wave Speed Measurement Matters

Purpose To evaluate the correlation between ultrasonographic (US) point shear-wave elastography (SWE) and magnetic resonance (MR) elastography liver shear-wave speed (SWS) measurements in a pediatric population and to determine if US data dispersion affects this relationship. Materials and Methods Institutional review board approval was obtained for this HIPAA-compliant investigation; informed consent and patient assent (as indicated) were obtained. Patients (age range, 0-21 years) undergoing clinical liver MR elastography between July 2014 and November 2015 were prospectively enrolled. Patients underwent two-dimensional gradient-recalled-echo 1.5-T MR elastography with point SWE performed immediately before or immediately after MR elastography. Spearman rank correlation coefficients were calculated to assess the relationship and agreement between point SWE and MR elastography SWS measurements. Uni- and multivariate logistic regression were performed to identify predictors of US data dispersion, with the best multivariate model selected based on Akaike information criterion. Results A total of 55 patients (24 female) were enrolled (mean age, 14.0 years ± 3.9 (standard deviation) (range, 3.5-21.4 years). There was fair correlation between point SWE and MR elastography SWS values for all patients (ρ = 0.33, P = .016). Correlation was substantial, however, when including only patients with minimal US data dispersion (n = 26, ρ = 0.61, P = .001). Mean body mass index (BMI) was significantly lower in patients with minimal US data dispersion than in those with substantial US data dispersion (25.4 kg/m2 ± 7.8 vs 32.3 kg/m2 ± 8.3, P = .003). At univariate analysis, BMI (odds ratio, 1.12; 95% confidence interval [CI]: 1.03, 1.21; P = .006) and abdominal wall thickness (odds ratio, 2.50; 95% CI: 1.32, 4.74; P = .005) were significant predictors of US data dispersion. In the best multivariate model, BMI was the only significant predictor (odds ratio, 1.11; 95% CI: 1.03, 1.20; P = .009). Conclusion Point SWE and MR elastography liver SWS measurements correlate well in patients with a BMI of less than 30 kg/m2 and minimal US data dispersion; increasing US data dispersion is directly related to a higher BMI. © RSNA, 2016.

Liver Stiffness Values Are Lower in Pediatric Subjects than in Adults and Increase with Age: A Multifrequency MR Elastography Study

Purpose To determine if healthy hepatic mechanical properties differ between pediatric and adult subjects at magnetic resonance (MR) elastography. Materials and Methods Liver shear moduli in 24 healthy pediatric participants (13 children aged 5-14 years [seven boys, six girls] and 11 adolescents aged 15-18 years [six boys, five girls]) and 10 healthy adults (aged 22-36 years [five men, five women]) were obtained with 3-T MR elastography at 28, 56, and 84 Hz. Relationships between shear moduli and age were assessed with Spearman correlations. Differences between age groups were determined with one-way analysis of variance and Tukey multiple comparisons tests. Results Liver stiffness values (means ± standard deviations) were significantly lower in children and adolescents than in adults at 56 Hz (children, 2.2 kPa ± 0.3; adolescents, 2.2 kPa ± 0.2; adults, 2.6 kPa ± 0.3; analysis of variance, P = .009) and 84 Hz (children, 5.6 kPa ± 0.8; adolescents, 6.5 kPa ± 1.2; adults, 7.8 kPa ± 1.2; analysis of variance, P = .0003) but not at 28 Hz (children, 1.2 kPa ± 0.2; adolescents, 1.3 kPa ± 0.3; adults, 1.2 kPa ± 0.2; analysis of variance, P = .40). At 56 and 84 Hz, liver stiffness increased with age (Spearman correlation, r = 0.38 [P = .03] and r = 0.54 [P = .001], respectively). Stiffness varied less with frequency in children and adolescents than in adults (analysis of variance, P = .0009). No significant differences were found in shear moduli at 28, 56, or 84 Hz or frequency dependence between children and adolescents (P = .38, P = .99, P = .14, and P = .30, respectively, according to Tukey tests). Conclusion Liver stiffness values are lower and vary less with frequency in children and adolescents than in adults. Stiffness increases with age during normal development and approaches adult values during adolescence. Comparing pediatric liver stiffness to adult baseline values to detect pediatric liver mechanical abnormalities may not allow detection of mild disease and may lead to underestimation of severity. ^© RSNA, 2016 Online supplemental material is available for this article.

Lysosomal Acid Lipase Deficiency Unmasked in Two Children With Nonalcoholic Fatty Liver Disease

Lysosomal acid lipase deficiency (LAL-D) is a classic lysosomal storage disorder characterized by accumulation of cholesteryl ester and triglyceride. Although it is associated with progressive liver injury, fibrosis, and end-stage liver disease in children and adolescents, LAL-D frequently presents with nonspecific signs that overlap substantially with other, more common, chronic conditions like nonalcoholic fatty liver disease (NAFLD), metabolic syndrome, and certain inherited dyslipidemias. We present 2 children with NAFLD who achieved clinically significant weight reduction through healthy eating and exercise, but who failed to have the anticipated improvements in aminotransferases and γ-glutamyl transferase. Liver biopsies performed for these "treatment failures" demonstrated significant microvesicular steatosis, prompting consideration of coexisting metabolic diseases. In both patients, lysosomal acid lipase activity was low and LIPA gene testing confirmed LAL-D. We propose that LAL-D should be considered in the differential diagnosis when liver indices in patients with NAFLD fail to improve in the face of appropriate body weight reduction.

Ultrasound Elastography Is Useful for Evaluation of Liver Fibrosis in Children-A Systematic Review

OBJECTIVES

Adult studies have proven ultrasound elastography as a validated measure of liver fibrosis. The present study aimed to review the available literature on ultrasound elastography in children to evaluate the ability of the method to distinguish healthy from fibrotic liver tissue and investigate whether cutoff values for liver fibrosis in children have been established.

METHODS

A literature search was performed in MEDLINE, EMBASE, the Cochrane Library, and Web of Science to identify studies on ultrasound elastography of the liver in children. Only original research articles in English concerning ultrasound elastography in children with and without liver disease, younger than 18 years, were included. All reference lists of the included articles were hand-searched for further references.

RESULTS

Twenty-seven articles were included. Elastography in children without liver disease was investigated in 14 studies and were comparable to those existing for adults. Twelve studies compared elastography with liver biopsy in children with liver disease and found that cirrhosis was correctly diagnosed, whereas it was more difficult to assess severe fibrosis correctly. For the distinction between no, mild, and moderate fibrosis in children with liver disease the method was less accurate. Ultrasound elastography was able to differentiate between children with and without liver fibrosis. In children without liver disease ultrasound, elastography showed consistent liver stiffness values comparable to those found in adults. No fibrosis-specific cutoffs were proposed.

CONCLUSIONS

Ultrasound elastography was able to diagnose cirrhosis, distinguish healthy from fibrotic liver tissue, and showed consistent liver stiffness values in children without liver disease.

[Functional MR imaging of the liver]

The diagnostics of diffuse liver disease traditionally rely on liver biopsies and histopathological analysis of tissue specimens. However, a liver biopsy is invasive and carries some non-negligible risks, especially for patients with decreased liver function and those requiring repeated follow-up examinations. Over the last decades, magnetic resonance imaging (MRI) has developed into a valuable tool for the non-invasive characterization of focal liver lesions and diseases of the bile ducts. Recently, several MRI methods have been developed and clinically evaluated that also allow the diagnostics and staging of diffuse liver diseases, e.g. non-alcoholic fatty liver disease, hepatitis, hepatic fibrosis, liver cirrhosis, hemochromatosis and hemosiderosis. The sequelae of diffuse liver diseases, such as a decreased liver functional reserve or portal hypertension, can also be detected and quantified by modern MRI methods. This article provides the reader with the basic principles of functional MRI of the liver and discusses the importance in a clinical context.

Similarities and differences between pediatric and adult nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is highly common and potentially serious in children and adolescents. The term NAFLD refers to a spectrum of diseases ranging from accumulation of fat in the liver (simple steatosis or nonalcoholic fatty liver "NAFL") to the potentially progressive form of nonalcoholic steatohepatitis (NASH) characterized by hepatocyte ballooning, inflammation, and often associated with fibrosis. While large prospective longitudinal studies in pediatric NAFLD are still lacking, growing evidence suggests that children with NAFL are at increased risk for cardiometabolic complications, while those with NASH and advance fibrosis are also at risk for significant liver-related morbidity including cirrhosis and its complications. Pediatric NAFLD shares features of adult NAFLD but also shows many different characteristics in terms of prevalence, histology, diagnosis and management. Translational studies suggest that NAFLD is a highly heritable disease in which genetic variations and environment closely interact to determine the disease phenotype and the progression to the more advanced forms of the disease. Changes in lifestyle, targeting gradual weight reduction, and physical exercise continue to be the mainstay of treatment for NAFLD in children. Recent advances in development of noninvasive diagnostic modalities and the potential for identifying effective pharmacological interventions may result in significant progress in the management of NAFLD in the pediatric population.

Liver Stiffness Measurements with MR Elastography: Agreement and Repeatability across Imaging Systems, Field Strengths, and Pulse Sequences

Purpose To prospectively assess agreement and repeatability of magnetic resonance (MR) elastography liver stiffness measurements across imager manufacturers, field strengths, and pulse sequences. Materials and Methods This prospective cross-sectional study was approved by the institutional review board; informed consent was obtained from all subjects. On the basis of an a priori power calculation, 24 volunteer adult subjects underwent MR elastography with four MR imaging systems (two vendors) and multiple pulse sequences (two-dimensional [2D] gradient-echo [GRE] imaging, 2D spin-echo [SE] echo-planar imaging, and three-dimensional [3D] SE echo-planar imaging). Each sequence was performed twice in each patient with each imaging system. Intraclass correlation coefficients (ICCs) were used to assess agreement and repeatability. P < .05 was considered indicative of a statistically significant difference. Results Pairwise ICCs were 0.67-0.82 and 0.62-0.83 for agreement between pulse sequences across manufacturers (n = 4) and field strengths (n = 5), respectively. ICCs were 0.45-0.90 for pairwise agreement between sequences while fixing manufacturer and field strength (n = 8). Test-retest repeatability across the various manufacturer, field strength, and pulse sequence combinations (n = 10) was excellent (ICCs, 0.77-0.94). The overall ICC for all manufacturer, field strength, and sequence combinations (n = 10) was 0.68 (95% confidence interval [CI]: 0.55, 0.82). ICC according to field strength was 0.78 (95% CI: 0.67, 0.88) at 1.5 T (n = 5) and 0.64 (95% CI: 0.49, 0.78) at 3.0 T (n = 5). ICCs according to vendor were 0.83 (95% CI: 0.73, 0.91) (n = 4) and 0.65 (95% CI: 0.51, 0.79) (n = 6). Average patient level variance was 0.042 kPa, with a coefficient of variation of 10.7%. Conclusion MR elastography is a reliable method for assessing liver stiffness, with small amounts of variability between imager manufacturers, field strengths, and pulse sequences. ^© RSNA, 2016.

Magnetic resonance elastography for staging liver fibrosis in non-alcoholic fatty liver disease: a diagnostic accuracy systematic review and individual participant data pooled analysis

OBJECTIVES

We conducted an individual participant data (IPD) pooled analysis on diagnostic accuracy of MRE to detect fibrosis stage in patients with non-alcoholic fatty liver disease (NAFLD).

METHODS

Through a systematic literature search, we identified studies of MRE (at 60-62.5 Hz) for staging fibrosis in patients with NAFLD, using liver biopsy as gold standard, and contacted study authors for IPD. Through pooled analysis, we calculated the cluster-adjusted AUROC, sensitivity and specificity of MRE for any (≥stage 1), significant (≥stage 2) and advanced (≥stage 3) fibrosis and cirrhosis (stage 4).

RESULTS

We included nine studies with 232 patients with NAFLD (mean age, 51 ± 13 years; 37.5% males; mean BMI, 33.5 ± 6.7 kg/m(2); interval between MRE and biopsy <1 year, 98.3%). Fibrosis stage distribution (stage 0/1/2/3/4) was 33.6, 32.3, 10.8, 12.9 and 10.4%, respectively. Mean AUROC (and 95% CIs) for diagnosis of any, significant or advanced fibrosis and cirrhosis was 0.86 (0.82-0.90), 0.87 (0.82-0.93), 0.90 (0.84-0.94) and 0.91 (0.76-0.95), respectively. Similar diagnostic performance was observed in stratified analysis based on sex, obesity and degree of inflammation.

CONCLUSIONS

MRE has high diagnostic accuracy for detection of fibrosis in NAFLD, independent of BMI and degree of inflammation.

KEY POINTS

• MRE has high diagnostic accuracy for detection of fibrosis in NAFLD. • BMI does not significantly affect accuracy of MRE in NAFLD. • Inflammation had no significant influence on MRE performance in NAFLD for fibrosis.

A comprehensive review of noninvasive liver fibrosis tests in pediatric nonalcoholic Fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) and its spectrum ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) and fibrosis have been increasing in the pediatric population. The presence and severity of fibrosis in patients with NAFLD are important prognostic factors for the risk of disease progression to cirrhosis. The gold standard for staging liver fibrosis is a liver biopsy. However, given the risks of this procedure, especially in the pediatric population, the development of noninvasive markers to diagnose and monitor progression of NAFLD is desirable. This paper will review recently developed noninvasive methods for diagnosing liver fibrosis in children with NAFLD. These include simple fibrosis scores, advanced biochemical markers, and radiologic imaging studies. Simple fibrosis scores use readily available laboratory tests; available one include AST/ALT ratio, AST to platelet ratio index (APRI), fibrosis (FIB)-4 index, NAFLD fibrosis score (NFS), pediatric NAFLD fibrosis index (PNFI), and pediatric NALFD fibrosis score (PNFS). Advanced biochemical markers include biomarkers of hepatocyte cell death such as cytokeratin 18 fragment levels, and markers of extracellular matrix turnover such as the Enhanced Liver Fibrosis (ELF) test and hyaluronic acid. Radiologic imaging studies estimate liver stiffness as a surrogate for liver fibrosis; these include transient elastography (TE), magnetic resonance elastography (MRE), and acoustic radiation force impulse imaging (ARFI).

Incorporation of Noninvasive Measures of Liver Fibrosis Into Clinical Practice: Diagnosis and Prognosis

Noninvasive methods are increasingly used for the assessment of liver fibrosis. Two categories of markers include serum-based markers (biologic properties) or ultrasound and magnetic resonance imaging-based techniques that use the principles of elastography (physical properties) to indirectly assess liver fibrosis. Serum markers can be either direct or indirect markers of the fibrosis process. Common elastography-based studies include vibration-controlled transient elastography, point shear wave elastography, and 2-dimensional shear wave elastography and magnetic resonance elastography. A common theme among all techniques is the inability to accurately differentiate between minimal or moderate stages of fibrosis but superior performance in identifying subjects with cirrhosis or normal liver parenchyma. Noninvasive markers may also serve as prognostic tools to course the natural history of chronic liver disease as well as identify cirrhotic patients at highest risk of future decompensation. Further research is needed to identify the role of noninvasive markers in following asymptomatic individuals, especially in patients with nonalcoholic fatty liver disease.