Pediatric MR elastography of hepatic fibrosis: principles, technique and early clinical experience

Liver fibrosis in children: a comprehensive review of mechanisms, diagnosis, and therapy

Chronic liver disease incidence is increasing among children worldwide due to a multitude of epidemiological changes. Most of these chronic insults to the pediatric liver progress to fibrosis and cirrhosis to different degrees. Liver and immune physiology differs significantly in children from adults. Because most of pediatric liver diseases have no definitive therapy, a better understanding of population and disease-specific fibrogenesis is mandatory. Furthermore, fibrosis development has prognostic significance and often guide treatment. Evaluation of liver fibrosis continues to rely on the gold-standard liver biopsy. However, many high-quality studies put forward the high diagnostic accuracy of numerous diagnostic modalities in this setting. Herein, we summarize and discuss the recent literature on fibrogenesis with an emphasis on pediatric physiology along with a detailed outline of disease-specific signatures, noninvasive diagnostic modalities, and the potential for antifibrotic therapies.

Magnetic resonance elastography in evaluation of liver fibrosis in children with chronic liver disease

BACKGROUND

Magnetic resonance elastography (MRE) has been used to stage liver fibrosis in adults. We aimed to assess the agreement between the Ishak scoring system and magnetic resonance elastography-measured liver stiffness (MRE-LS) in children. This study included all the children who underwent abdominal MRE and liver biopsies between February 2018 and January 2021. The correlation between MRE-LS and Ishak fibrosis stage, MRE parameters, and clinical and biochemical markers affecting this relationship was investigated.

RESULTS

A total of 52 patients (31 male; a median age of 11.8 years) were included in the study. The MRE-LS values were significantly different between Ishak fibrosis stages (p = 0.036). With a cut-off value of 2.97 kilopascals, MRE-LS had sensitivity, specificity, PPV, NPV and accuracy values of 90.9%, 82.9%, 58.8%, 97.1%, and 84.6%, respectively, for differentiating mild/moderate fibrosis (F0, 1, 2, 3) from severe fibrosis (F ≥ 4). Although MRE-LS was moderately correlated with Ishak fibrosis score and histological activity index and weakly correlated with aspartate aminotransferase, hepatic steatosis, and R2*, only Ishak fibrosis score was a significant predictor of MRE-LS. MRE-measured spleen stiffness was weakly correlated with the Ishak fibrosis score.

CONCLUSIONS

MRE has high sensitivity and specificity for evaluating liver fibrosis in children. MRE may be used to evaluate liver fibrosis in pediatric patients.

Noninvasive Prediction of Advanced Fibrosis in Pediatric Liver Disease-Discriminatory Performance of 2D Shear Wave Elastography, Transient Elastography and Magnetic Resonance Elastography in Comparison to Histopathology

Background: Elastography can be measured with different imaging techniques and is increasingly used for noninvasive assessment of hepatic fibrosis. Little is known about the performance, and interrelation of different elastographic techniques, in prediction of hepatic fibrosis in pediatric liver disease. Objectives: We aimed to determine the discriminatory value for advanced fibrosis (Metavir F3-4) and evaluate the applicability of 2D shear wave ultrasound elastography (USe), Transient Elastography (TE) and Magnetic Resonance elastography (MRe) in pediatric liver disease. Methods: In patients with pediatric liver disease aged 0−19 years, USe, TE and MRe were compared with histopathological fibrosis stage. Multivariate logistic regression models for advanced fibrosis were considered. Discriminative performance was assessed by the area under the receiver operating characteristic curve and the Brier Score. Primary analyses included complete cases. Multiple imputation was used as sensitivity analysis. Results: In 93 histologically evaluated patients USe, TE and MRe were performed 89, 93 and 61 times respectively. With increased liver stiffness values, significantly increased odds for presenting F3-4 were seen in individual models for ALT < 470 U/L, whereas the effect for ALT > 470 U/L was non-significant. Area under the curve and Brier Score for discrimination of advanced fibrosis were 0.798 (0.661−0.935) and 0.115 (0.064−0.166); 0.862 (0.758−0.966) and 0.118 (0.065−0.171); 0.896 (0.798−0.994) and 0.098 (0.049−0.148) for USe, TE and MRe respectively. No significant increase in discriminatory ability was found when combining elastographic modalities. Conclusions: In pediatric liver disease, USe, TE and MRe had a good discriminatory ability for assessment of advanced liver fibrosis, although TE and MRe performed best. In most children with pediatric liver disease, TE is a reliable and easily applicable measure.

Attenuation Coefficient Measurement Using a High-Frequency (2-9 MHz) Convex Transducer for Children Including Fatty Liver

We evaluated the measurement feasibility and diagnostic ability of an ultrasound-guided attenuation parameter (UGAP) using a high-frequency convex transducer in children. This retrospective study included all consecutive children who underwent abdomen ultrasonography from July to December 2020. Attenuation coefficients (ACs) of the liver were measured using both 1- to 6-MHz (AC1-6) and 2- to 9-MHz (AC2-9) probes of the LOGIQ E10 system (GE Healthcare). t-Tests and Pearson's or partial correlation analyses were performed, and AC cutoff values for diagnosing fatty liver were obtained from receiver operating characteristic curve analyses. Finally, 118 patients (M:F = 83:35, mean age: 10.2 ± 4.1 y) were evaluated, and the measurement success rate was 98.3% (116/118) for AC2-9. AC1-6 was available in children with a liver depth greater than 9 cm. The ratio of interquartile range to median of the AC2-9 was lower than that of the AC1-6 (4.3 vs. 8.5, p < 0.001). In the normal group (n = 41), the AC2-9 values were not associated with age, sex or body mass index. For the evaluation of steatosis, the AC2-9 values exhibited a positive correlation with the MR fat fraction (coefficient = 0.498, p < 0.001). The cutoff value of 0.699 dB/cm/MHz had 90.2% sensitivity and 100% specificity for diagnosing fatty liver. In conclusion, measurements of ACs using a high-frequency convex transducer are feasible even in small children, with lower measurement variability. The AC2-9 values also had good diagnostic performance for pediatric fatty liver.

A tailored passive driver for liver MRE in pediatric patients

Objectives

Magnetic resonance elastography (MRE) is increasingly used in the pediatric population for diagnosis and staging of liver fibrosis. However, the MR-compatible driver and sequences are usually those used for adult patients. Our feasibility study aimed to adapt the standardized adult MRE passive driver and vibrational parameters to a pediatric population.

Methods

We designed an elliptic passive driver shaped on a torus equipped with an elastic membrane and adapted to children's morphologies. As a first step, eight children (aged 8-18 years) were enrolled in a prospective pilot study aiming to determine the threshold vibrational amplitude for MRE using a custom passive driver, based on phase aliasing assessment and the occurrence of signal void artifacts on magnitude MR images. In the second step, the practicality and the consistency of the custom driver were assessed in a further 11 pediatric patients (aged 7-18 years). In the third step, we compared our custom driver vs. the commercial driver on six adult volunteers, in terms of the reliable region of interest area within the acquired MRE slices, the shear wave maps' quality, and measured stiffness values obtained.

Results

Based on pediatric patient data, the threshold vibrational amplitude expressed as percentage of maximum output was found to be 0.4 and 1.1 times the body weight (kg) at 40 and 60 Hz frequencies, respectively. In comparison to the commercial passive driver, the custom driver improved threefold the contact with the body surface, also enabling a more comfortable examination as self-assessed by the volunteers.

Conclusions

Our custom driver was more comfortable for the volunteers and was able to generate more homogenous shear waves, yielding larger usable hepatic area, and more reliable stiffness values.

Effect of different driver power amplitudes on liver stiffness measurement in pediatric liver MR elastography

PURPOSE

To assess how different driver power amplitudes affect the measurement of liver stiffness in pediatric liver magnetic resonance elastography (MRE).

METHODS

From January 2018 to May 2018, pediatric patients (≤ 18 years) who underwent liver MRE with 20% and 56% driver power amplitudes were included in this retrospective study. Region-of-interests (ROIs) were drawn on four stiffness maps to include the largest area of the liver parenchyma. Intraclass correlation coefficients (ICCs) were used to assess agreements for the area, mean, maximum, minimum and standard deviation of liver stiffness between the driver power amplitudes.

RESULTS

128 MRE stiffness maps from 16 patients (M:F = 10:6, median 12.5 years old) were included. On MRE, median ROI areas of liver were 83.1 cm² (range, 46.9-144.1 cm²) and 63.0 cm² (range, 5.4-123.4 cm²) for the driver power amplitudes of 20% and 56%, respectively. Median liver stiffness values were 2.3 kPa (range, 1.7-8.0 kPa) and 2.8 kPa (range, 1.7-8.5 kPa). Maximum and minimum liver stiffness values were 5.3 kPa and 1.0 kPa for 20% and 7.8 kPa and 1.1 kPa for 56%. Standard deviation was 0.6 kPa for 20% and 1.0 kPa for 56%. ICC values between the two power amplitudes were 0.33-0.51 for the ROI area and the maximum, minimum and standard deviation values of liver stiffness. The ICC value for liver stiffness was 0.857 (95% confidence interval, 0.760-0.915).

CONCLUSION

Liver stiffness with two driver power amplitudes on MRE showed good reliability in pediatric patients. Driver power amplitudes need to be optimized according to the pediatric liver size.

Quantitative MRI Assessment of Pancreatic Steatosis Using Proton Density Fat Fraction in Pediatric Obesity

Objective

To assess the feasibility of quantitatively assessing pancreatic steatosis using magnetic resonance imaging (MRI) and its correlation with obesity and metabolic risk factors in pediatric patients.

Materials and Methods

Pediatric patients (≤ 18 years) who underwent liver fat quantification MRI between January 2016 and June 2019 were retrospectively included and divided into the obesity and control groups. Pancreatic proton density fat fraction (P-PDFF) was measured as the average value for three circular regions of interest (ROIs) drawn in the pancreatic head, body, and tail. Age, weight, laboratory results, and mean liver MRI values including liver PDFF (L-PDFF), stiffness on MR elastography, and T2^* values were assessed for their correlation with P-PDFF using linear regression analysis. The associations between P-PDFF and metabolic risk factors, including obesity, hypertension, diabetes mellitus (DM), and dyslipidemia, were assessed using logistic regression analysis.

Results

A total of 172 patients (male:female = 125:47; mean ± standard deviation [SD], 13.2 ± 3.1 years) were included. The mean P-PDFF was significantly higher in the obesity group than in the control group (mean ± SD, 4.2 ± 2.5% vs. 3.4 ± 2.4%; p = 0.037). L-PDFF and liver stiffness values showed no significant correlation with P-PDFF (p = 0.235 and p = 0.567, respectively). P-PDFF was significantly associated with obesity (odds ratio 1.146, 95% confidence interval 1.006–1.307, p = 0.041), but there was no significant association with hypertension, DM, and dyslipidemia.

Conclusion

MRI can be used to quantitatively measure pancreatic steatosis in children. P-PDFF is significantly associated with obesity in pediatric patients.

Diagnostic Performance of Noninvasive Methods for Liver Biopsy by Fibroscan in Pediatric

Liver biopsy is the gold standard for the diagnosis and management of various liver diseases; however, noninvasive diagnostic modalities may help prevent adverse effects of anesthesia, prolonged hospitalization, sampling error, and other serious complications, particularly in pediatric patients. The aim of this study is to compare the results of liver biopsy and fibroscan in children with chronic liver diseases. All patients presenting chronic liver disease admitted in the ward or clinic of Tehran's Children Medical Center were enrolled in the study. Required laboratory tests were performed to diagnose the disease, followed by elastography using fibroscan 402 (M-probe) Echosens machine and liver biopsy using Menghini technique. Samples were scored by using METAVIR scoring system. Thirty-two patients were reported (68.8%, female) with autoimmune hepatitis (18.8%), Wilson disease (12.5%), and glycogen storage disease (12.5%). The most common pathologic stage and fibroscan result was stage III and F0 (46.9%), respectively. Association between pathology and fibroscan results was not significant. Nonetheless, age and diagnosis, age and Fibroscan score, and pathology and liver function test were significantly associated with each other. Fibroscan cannot be used as an alternative to liver biopsy; however, it can be a useful accessory tool.

A noninvasive index to predict liver cirrhosis in biliary atresia

BACKGROUND

Biliary atresia is a progressive obliterative cholangiopathy affecting both extrahepatic and intrahepatic biliary trees, resulting in fibrous obliteration of the biliary tract and subsequent development of cirrhosis.

OBJECTIVE

The aim of this study was to find noninvasive indices to predict the status of hepatic fibrosis in children with biliary atresia.

MATERIALS AND METHODS

We retrospectively measured the volume of the hepatic lobes and spleen from MR images, obtained biochemical data and analyzed the relationship between the imaging and biochemical indices, and the pathological status of hepatic fibrosis in 35 children with biliary atresia.

RESULTS

A combined index was obtained by logistic regression: logit (likelihood of cirrhosis) = 0.00043 x age at MR examination + 1.67 x aspartate aminotransferase and platelet ratio index (APRI) + 0.0029 x body-surface-area-adjusted left liver lobe volume (BSA adLLV) - 6.57 (log-likelihood chi-square P<0.05, pseudo-R²=0.59). The area under the receiver operator characteristic curve of age at MR examination, APRI, BSA adLLV and the combined index for prediction of cirrhosis were 0.91, 0.86, 0.83 and 0.94, respectively. The optimal cut-off value (sensitivity and specificity) of age at MR examination, APRI, BSA adLLV and combined index were 132 (86% and 92%), 1.3 (91% and 85%), 855.5 (96% and 62%) and 0.689 (91% and 92%). The accuracy of age at MR examination, APRI, BSA adLLV and combined index were 89%, 89%, 83% and 91%, respectively.

CONCLUSION

A combined noninvasive index of age, aspartate aminotransferase and platelet ratio index, and the body-surface-area-adjusted left liver lobe volume measured from MR images is a potential marker of liver cirrhosis in children with biliary atresia.

Validation and feasibility of liver T1 mapping using free breathing MOLLI sequence in children and young adults

We investigated the feasibility of free-breathing modified Look-Locker inversion recovery (MOLLI) sequence for measuring hepatic T1 values in children and young adults. To investigate the accuracy and the reproducibility of the T1 maps, a phantom study was performed with 12 different gadoterate meglumine concentrations and the T1 relaxation times of phantoms measured with the MOLLI sequence were compared against those measured with three different sequences: spin-echo inversion recovery, variable flip angle (VFA), and VFA with B1 correction. To evaluate the feasibility of free-breathing MOLLI sequence, hepatic T1 relaxation times obtained by free-breathing and breath-hold technique in twenty patients were compared. The phantom study revealed the excellent accuracy and reproducibility of MOLLI. In twenty patients, the mean value of hepatic T1 values obtained by free-breathing (606.7 ± 64.5 ms) and breath-hold (609.8 ± 64.0 ms) techniques showed no significant difference (p > 0.05). The Bland–Altman plot between the free-breathing and breath-hold revealed that the mean difference of T1 values was − 3.0 ms (− 0.5%). Therefore, T1 relaxation times obtained by MOLLI were comparable to the values obtained using the standard inversion recovery method. The hepatic T1 relaxation times measured by MOLLI technique with free-breathing were comparable to those obtained with breath-hold in children and young adults.

Quantitative Imaging in Pediatric Hepatobiliary Disease

Pediatric hepatobiliary imaging is important for evaluation of not only congenital or structural disease but also metabolic or diffuse parenchymal disease and tumors. A variety of ultrasonography and magnetic resonance imaging (MRI) techniques can be used for these assessments. In ultrasonography, conventional ultrasound imaging as well as vascular imaging, elastography, and contrast-enhanced ultrasonography can be used, while in MRI, fat quantification, T2/T2^* mapping, diffusion-weighted imaging, magnetic resonance elastography, and dynamic contrast-enhanced MRI can be performed. These techniques may be helpful for evaluation of biliary atresia, hepatic fibrosis, nonalcoholic fatty liver disease, sinusoidal obstruction syndrome, and hepatic masses in children. In this review, we discuss each tool in the context of management of hepatobiliary disease in children, and cover various imaging techniques in the context of the relevant physics and their clinical applications for patient care.

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.

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.

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).

Static and dynamic liver stiffness: An ex vivo porcine liver study using MR elastography

Magnetic resonance elastography (MRE) is an MRI-based noninvasive technique for quantitatively assessing tissue stiffness. The hypothesis of this study is that stiffness increases with portal pressure. We further hypothesized that the rate of stiffness change with pressure would be larger in liver tissue treated to simulate the stiffening effects of fibrosis. In agreement with our hypothesis, the formalin-treated livers were stiffer than the untreated livers, and in both groups the liver stiffness increased with portal venous pressure. The rate of stiffness change with portal pressure was significantly greater after formalin treatment. In this study, we have developed an ex vivo liver model incorporating portal venous pressure variations and observed significant changes in liver stiffness due to portal pressure. This model could be useful for understanding and investigating the changes in the static and dynamic components of liver stiffness.

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.

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.

MRI of paediatric liver tumours: How we review and report

Liver tumours are fortunately rare in children. Benign tumours such as haemangiomas and cystic mesenchymal hamartomas are typically seen in infancy, often before 6 months of age. After that age, malignant hepatic tumours increase in frequency. The differentiation of a malignant from benign lesion on imaging can often negate the need for biopsy. Ultrasound is currently the main screening tool for suspected liver pathology, and is ideally suited for evaluation of hepatic lesions in children due to their generally small size. With increasing research, public awareness and parental anxiety regarding radiation dosage from CT imaging, MRI is now unquestionably the modality of choice for further characterisation of hepatic mass lesions.

Nevertheless the cost, length of imaging time and perceived complexity of a paediatric liver MR study can be intimidating to the general radiologist and referring clinician. This article outlines standard MR sequences utilised, reasons for their utilisation, types of mixed hepatocyte specific/extracellular contrast agents employed and imaging features that aid the interpretation of paediatric liver lesions. The two commonest paediatric liver malignancies, namely hepatoblastoma and hepatocellular carcinoma are described. Differentiation of primary hepatic malignancies with metastatic disease and mimickers of malignancy such as focal nodular hyperplasia (FNH) and hepatic adenomas are also featured in this review..

Imaging should aim to clarify the presence of a lesion, the likelihood of malignancy and potential for complete surgical resection. Reviewing and reporting the studies should address these issues in a systematic fashion whilst also commenting upon background liver parenchymal appearances. Clinical information and adequate patient preparation prior to MR imaging studies help enhance the diagnostic yield.

White Paper on P4 Concepts for Pediatric Imaging

Over the past decade, innovations in the field of pediatric imaging have been based largely on single-center and retrospective studies, which provided limited advances for the benefit of pediatric patients. To identify opportunities for potential "quantum-leap" progress in the field of pediatric imaging, the ACR-Pediatric Imaging Research (PIR) Committee has identified high-impact research directions related to the P4 concept of predictive, preventive, personalized, and participatory diagnosis and intervention. Input from 237 members of the Society for Pediatric Radiology was clustered around 10 priority areas, which are discussed in this article. Needs within each priority area have been analyzed in detail by ACR-PIR experts on these topics. By facilitating work in these priority areas, we hope to revolutionize the care of children by shifting our efforts from unilateral reaction to clinical symptoms, to interactive maintenance of child health.

Ultrasound Elastography and MR Elastography for Assessing Liver Fibrosis: Part 2, Diagnostic Performance, Confounders, and Future Directions

OBJECTIVE

The purpose of the article is to review the diagnostic performance of ultra-sound and MR elastography techniques for detection and staging of liver fibrosis, the main current clinical applications of elastography in the abdomen.

CONCLUSION

Technical and instrument-related factors and biologic and patient-related factors may constitute potential confounders of stiffness measurements for assessment of liver fibrosis. Future developments may expand the scope of elastography for monitoring liver fibrosis and predict complications of chronic liver disease.

Cirrhosis in children and adolescents: An overview

Several conditions, especially chronic liver diseases, can lead to cirrhosis in children and adolescents. Most cases in clinical practice are caused by similar etiologies. In infants, cirrhosis is most often caused by biliary atresia and genetic-metabolic diseases, while in older children, it tends to result from autoimmune hepatitis, Wilson's disease, alpha-1-antitrypsin deficiency and primary sclerosing cholangitis. The symptoms of cirrhosis in children and adolescents are similar to those of adults. However, in pediatric patients, the first sign of cirrhosis is often poor weight gain. The complications of pediatric cirrhosis are similar to those observed in adult patients, and include gastrointestinal bleeding caused by gastroesophageal varices, ascites and spontaneous bacterial peritonitis. In pediatric patients, special attention should be paid to the nutritional alterations caused by cirrhosis, since children and adolescents have higher nutritional requirements for growth and development. Children and adolescents with chronic cholestasis are at risk for several nutritional deficiencies. Malnutrition can have severe consequences for both pre- and post-liver transplant patients. The treatment of cirrhosis-induced portal hypertension in children and adolescents is mostly based on methods developed for adults. The present article will review the diagnostic and differential diagnostic aspects of end-stage liver disease in children, as well as the major treatment options for this condition.

Superficial ultrasound shear wave speed measurements in soft and hard elasticity phantoms: repeatability and reproducibility using two ultrasound systems

BACKGROUND

There is a paucity of data available regarding the repeatability and reproducibility of superficial shear wave speed (SWS) measurements at imaging depths relevant to the pediatric population.

OBJECTIVE

To assess the repeatability and reproducibility of superficial shear wave speed measurements acquired from elasticity phantoms at varying imaging depths using three imaging methods, two US systems and multiple operators.

MATERIALS AND METHODS

Soft and hard elasticity phantoms manufactured by Computerized Imaging Reference Systems Inc. (Norfolk, VA) were utilized for our investigation. Institution No. 1 used an Acuson S3000 US system (Siemens Medical Solutions USA, Malvern, PA) and three shear wave imaging method/transducer combinations, while institution No. 2 used an Aixplorer US system (SuperSonic Imagine, Bothell, WA) and two different transducers. Ten stiffness measurements were acquired from each phantom at three depths (1.0 cm, 2.5 cm and 4.0 cm) by four operators at each institution. Student's t-test was used to compare SWS measurements between imaging techniques, while SWS measurement agreement was assessed with two-way random effects single-measure intra-class correlation coefficients (ICCs) and coefficients of variation. Mixed model regression analysis determined the effect of predictor variables on SWS measurements.

RESULTS

For the soft phantom, the average of mean SWS measurements across the various imaging methods and depths was 0.84 ± 0.04 m/s (mean ± standard deviation) for the Acuson S3000 system and 0.90 ± 0.02 m/s for the Aixplorer system (P = 0.003). For the hard phantom, the average of mean SWS measurements across the various imaging methods and depths was 2.14 ± 0.08 m/s for the Acuson S3000 system and 2.07 ± 0.03 m/s Aixplorer system (P > 0.05). The coefficients of variation were low (0.5-6.8%), and interoperator agreement was near-perfect (ICCs ≥ 0.99). Shear wave imaging method and imaging depth significantly affected measured SWS (P < 0.0001).

CONCLUSION

Superficial shear wave speed measurements in elasticity phantoms demonstrate minimal variability across imaging method/transducer combinations, imaging depths and operators. The exact clinical significance of this variation is uncertain and may change according to organ and specific disease state.

Value of hepatic diffusion-weighted magnetic resonance imaging in evaluating liver fibrosis following transarterial chemoembolization with low doses of chemotherapy

The aim of the present study was to investigate the value of apparent diffusion coefficients (ADCs) measured with magnetic resonance (MR) diffusion-weighted imaging (DWI) in evaluating liver fibrosis and curative effects on hepatocellular carcinoma (HCC) following transcatheter arterial chemoembolization (TACE) with low doses of chemotherapy. In total, 84 patients with HCC not recommended for surgical resection underwent TACE. The patients were divided into small dose (n=46) and conventional dose (n=38) chemotherapy groups, and underwent MR-DWI prior to and following TACE. Examination of the four liver fibrosis indexes, hyaluronate, laminin, human procollagen type-III and collagen type-IV, as well as ADC values (b=600 sec/mm²), was conducted in the two groups. With small dose chemotherapy, the ADC values were not significantly different preoperatively and postoperatively (P>0.05). By contrast, with a conventional dose, statistically significant differences were observed between the preoperative and postoperative ADC values (P<0.01). ADC values in the small and conventional dose chemotherapy groups prior to the first cycle of TACE were 1.613±0.133×10⁻³ and 1.488±0.248×10⁻³ mm²/sec, respectively, while following four cycles of TACE, the ADC values were 1.598±0.147×10⁻³ and 1.206±0.222×10⁻³ mm²/sec, respectively. With regard to chemotherapy, the ADC values before and after TACE were significantly different (P<0.05). A significant negative correlation was observed between the ADC values and the fibrosis stage (P<0.05). Therefore, hepatic MR-DWI plays a key role in evaluating liver fibrosis following TACE with low doses of chemotherapy, resulting in improved curative effects of TACE.

Real-time tissue elastography (RTE) for noninvasive evaluation of fibrosis in liver diseases in children in comparison to liver biopsy

PURPOSE

To determine the value of real-time tissue elastography (RTE) in pediatric liver diseases in comparison to liver biopsy.

METHODS

RTE was performed on 34 patients (♀, n = 17; ♂, n = 17; range 0-21 years) with various acute and chronic liver diseases: autoimmune hepatitis (n = 5), liver transplantation (n = 5), Wilson's disease (n = 4), hepatopathy of unknown origin (n = 4), unclear cholestatic hepatitis (n = 2), thalassemia major (n = 2), glycogenosis (n = 2), hereditary fructose intolerance (n = 1), alpha-1-antitrypsin deficiency (n = 1), diabetes mellitus type 1 (n = 1), chronic intestinal pseudo-obstruction (n = 1), primary sclerosing cholangitis (n = 1), hepatitis B (n = 1), cirrhosis of unknown origin (n = 1), drug-induced hepatopathy (n = 1), unexplained transaminase elevation (n = 1), and nonalcoholic steatohepatitis (n = 1). Included children were biopsied. RTE was performed on a control group (n = 30; ♀, n = 15; ♂, n = 15). The mean value of strain (MEAN) in arbitrary units and the ratio of blue color-coded harder tissue (AREA) were calculated based on an elasticity histogram of the selected region of interest in liver parenchyma. They were compared with the histologically defined grade of liver fibrosis.

RESULTS

In comparison to the scoring systems, a moderate correlation was observed for MEAN and AREA by excluding the F0 patients [MEAN r = -0.575 to -0.645, AREA r = 0.545-0.607 (p < 0.05)]. Differentiation of the control group and low-grade fibrosis (F1) from high-grade fibrosis (F2-4) was significantly possible (p values <0.001 at 5 % significance level).

CONCLUSION

RTE parameters enable a possible differentiation of high fibrosis; however, their correlation with fibrosis stage was moderate. RTE seems to be a promising method in liver fibrosis grading in children.

Apparent diffusion coefficient value of hepatic fibrosis and inflammation in children with chronic hepatitis

PURPOSE

This study was done to prospectively evaluate the usefulness of apparent diffusion coefficient (ADC) in the diagnosis and grading of hepatic fibrosis and inflammation in children with chronic hepatitis.

MATERIALS AND METHODS

Institutional Review Board approval was obtained. This prospective study was carried out on 50 children with chronic hepatitis (mean age 8.3 ± 3.2 years; 33 boys and 17 girls) and 20 age- and sex-matched healthy control children. The children underwent diffusion-weighted magnetic resonance imaging of the liver. The ADC value of the liver was calculated. The hepatic fibrosis stages (F1-F6) and necroinflammatory activity grades (A1-A4) were calculated. The ADC values of different stages of hepatic fibrosis and grades of necroinflammatory activity were calculated.

RESULTS

The mean ADC value of the liver parenchyma was 1.53 ± 0.17 × 10(-3) mm(2)/s in children with chronic hepatitis and 1.74 ± 0.16 × 10(-3) mm(2)/s in controls. The ADC value was significantly lower in children with hepatic fibrosis compared to controls (p = 0.001). There was a significant difference (p = 0.001) in ADC between mild (F1-F3) and advanced (F4-F6) stages of fibrosis. There was a significant difference (p = 0.004) in ADC between mild (A1-A2) and advanced (A3-A4) grades of necroinflammation. The cut-off ADC values used to differentiate mild from advanced fibrosis and necroinflammation were 1.62 and 1.64 mm(2)/s with an area under the curve of 0.898 and 0.807, respectively. The ADC value negatively correlated with stages of hepatic fibrosis (r = -0.799, p = 0.001) and necroinflammatory activity grade (r = -0.468, p = 0.001).

CONCLUSIONS

We conclude that ADC value is an effective noninvasive parameter for the diagnosis and grading of hepatic fibrosis and inflammation in children with chronic hepatitis.

Magnetic resonance elastography of liver: clinical applications

Magnetic resonance elastography (MRE) has been successfully implemented in the assessment of diffuse liver diseases. Currently, MRE is the most accurate noninvasive technique for detection and staging of liver fibrosis with a potential to replace liver biopsy. Magnetic resonance elastography is able to differentiate isolated fatty liver disease from steatohepatitis with or without fibrosis. Potential clinical applications include the differentiation of benign and malignant focal liver masses and the assessment of treatment response in diffuse liver diseases.

Pediatric hepatobiliary magnetic resonance imaging

Magnetic resonance (MR) imaging is an effective and noninvasive modality for evaluating hepatobiliary pathologic conditions. This article provides an up-to-date review of anatomy, indications, and imaging goals and protocols, including patient preparation, pulse sequences, and contrast agents used in pediatric MR hepatobiliary imaging. This article also highlights some of the common MR features of pediatric liver pathologic conditions, including tumors, congenital biliary ductal plate malformations, trauma, fibrosis, and infection.

Magnetic resonance imaging of the pediatric liver: imaging of steatosis, iron deposition, and fibrosis

Traditionally, many diffuse diseases of the liver could only be diagnosed by liver biopsy. Although still considered the gold standard, liver biopsy is limited by its small sample size, invasive nature, and subjectivity of interpretation. There have been significant advances in functional magnetic resonance (MR) imaging of the liver. These advances now provide radiologists with the tools to evaluate the liver at the molecular level, allowing quantification of hepatic fat and iron, and enabling the identification of liver fibrosis at its earliest stages. These methods provide objective measures of diffuse liver processes and aid hepatologists in the diagnosis and management of liver disease.

Magnetic resonance elastography in the diagnosis of hepatic fibrosis

Liver fibrosis is a common feature of many chronic liver diseases, and can ultimately progress to cirrhosis. Conventional imaging is insensitive to liver fibrosis, necessitating a liver biopsy for diagnosis and monitoring of progression. However, liver biopsy risks complications, and is an imperfect gold standard in view of sampling error and intraobserver or interobserver variation. Magnetic resonance elastography (MRE) is a noninvasive method for assessing the mechanical properties of tissues and is gaining credence as a method of assessment for hepatic fibrosis. The aim of this review is to describe how MRE is performed, to review the present literature on the subject, to compare MRE with other noninvasive techniques used to assess for liver fibrosis, and to highlight areas of future research.

Normal values of liver elasticity measured by real-time tissue elastography (RTE) in healthy infants and children

PURPOSE

To define normal values of liver elasticity measured by real-time tissue elastography (RTE) in healthy infants and children.

METHODS

RTE was performed on 91 children and adolescents by two experienced observers (female, n = 43; male, n = 48) and in two age groups (0-10 years, n = 45; 11-20 years, n = 46). Hepatopathies were excluded clinically by extensive laboratory testing and by ultrasound. RTE provides a histogram from a region of interest (ROI) in the liver representing the degree of stiffness of the liver. The distribution of the colors in the histogram corresponds to organ elasticity. By calculating the mean of stiffness values, a numerical value is expressed in arbitrary units (a.u.) representing the mean elasticity of the liver (MEAN). Additionally, the percentage values of relatively stiffer areas (color coded in blue) in the ROI can be calculated (%AREA). A Mann-Whitney U test was performed for these two parameters according to gender. The reproducibility of these values was determined with an intraclass correlation coefficient (ICC) test on another group of 18 healthy volunteers.

RESULTS

The median elasticity was 106 a.u. Gender did not have an influence on the parameters (MEAN: p = 0.052; %AREA: p = 0.051). Age-specific analyses did not yield any significant difference between the two age groups for either of the two analyzed parameters (MEAN: p = 0.059; %AREA: p = 0.058). The ICC test demonstrated a moderate agreement for MEAN (ICC = 0.582) and %AREA (ICC = 0.659).

CONCLUSION

Real-time elastography is a new sonography-based method and may be used as a supportive analysis to assess liver parenchyma elasticity in children, especially when fibrosis is suspected. We measured RTE normal values in children as reference data.

Noninvasive diagnosis of pediatric nonalcoholic fatty liver disease

Because nonalcoholic steatohepatitis can progress towards cirrhosis even in children, early detection of hepatic fibrosis and accurate diagnosis of nonalcoholic fatty liver disease (NAFLD) are important. Although liver biopsy is regarded as the gold standard of diagnosis, its clinical application is somewhat limited in children due to its invasiveness. Noninvasive diagnostic methods, including imaging studies, biomarkers of inflammation, oxidative stress, hepatic apoptosis, hepatic fibrosis, and noninvasive hepatic fibrosis scores have recently been developed for diagnosing the spectrum of NAFLD, particularly the severity of hepatic fibrosis. Although data and validation are still lacking for these noninvasive modalities in the pediatric population, these methods may be applicable for pediatric NAFLD. Therefore, noninvasive imaging studies, biomarkers, and hepatic fibrosis scoring systems may be useful in the detection of hepatic steatosis and the prediction of hepatic fibrosis, even in children with NAFLD.

Magnetic resonance elastography noninvasively detects in vivo renal medullary fibrosis secondary to swine renal artery stenosis

OBJECTIVES

Magnetic resonance elastography (MRE) can noninvasively sample tissue stiffness in vivo. Renal fibrosis secondary to renal artery stenosis (RAS), which is aggravated in atherosclerotic RAS (ARAS), may increase its stiffness. An increase in cortical stiffness in vivo can be masked by intrinsic hemodynamic determinants, whereas renal medullary stiffness is less dependent on renal hemodynamics. Therefore, this study tested the hypothesis that MRE-determined medullary stiffness would correspond to the histological degree of medullary fibrosis in stenotic kidneys in RAS and detect its exacerbation in ARAS.

MATERIALS AND METHODS

Seventeen pigs were studied 10 weeks after induction of unilateral RAS (n = 6), ARAS (n = 5), or sham (n = 6). Stiffness of the cortex and the medulla was determined through 3-dimensional MRE, and renal perfusion and function were determined using multidetector computed tomography. Kidney fibrosis was subsequently assessed ex vivo using the Masson trichrome staining.

RESULTS

Renal stenotic cortex and medulla were significantly more fibrotic in RAS and ARAS compared with healthy kidney. However, MRE detected increased stiffness in RAS compared with the healthy kidney (12.7 ± 0.41 kPa vs 10.7 ± 0.18 kPa; P = 0.004) only in the medulla, which was further increased in ARAS (16.6 ± 1.3 kPa; P = 0.017 vs RAS). Magnetic resonance elastography-derived medullary, but not cortical, stiffness significantly correlated with histological degree of fibrosis, although cortical and medullary fibroses were correlated. Renal blood flow and function were similarly decreased in RAS and ARAS compared with the healthy kidney.

CONCLUSIONS

Noninvasive 3-dimensional MRE detects increased renal medullary stiffness in RAS and ARAS in vivo, which correlates with its fibrosis ex vivo and may also reflect cortical fibrosis. Hence, MRE-derived medullary stiffness can be potentially useful in detecting renal fibrosis and track disease progression.

Transient elastography is a useful noninvasive tool for the evaluation of fibrosis in paediatric chronic liver disease

BACKGROUND

Outcome of liver disease in children is mainly determined by severity and progression of liver fibrosis. Liver biopsy is the accepted standard for evaluating fibrosis but is limited by the need for sedation in children, sampling error, and risks including bleeding. The aim of the present study was to compare tools for noninvasive assessment of liver fibrosis in a paediatric cohort.

METHODS

Children undergoing liver biopsy for chronic liver disease were recruited and underwent transient elastography (TE). Liver biopsies were scored by a hepatohistopathologist from F0 (no fibrosis) to F4 (cirrhosis). TE was compared with biopsy score.

RESULTS

During the study period, 104 children (62 boys) were enrolled (median age 13.6 years). Diagnosis was autoimmune liver disease in 27; nonalcoholic fatty liver disease in 37; posttransplant in 16; hepatitis B/C in 8; Wilson disease in 5; and the remainder, miscellaneous. TE was successful in all but 7 patients and was a good discriminator of significant fibrosis (≥ F2) (P < 0.001), severe fibrosis (≥ F3) (P < 0.001), and cirrhosis (F4) (P = 0.003). The area under the receiver operating characteristic curve for the prediction of ≥ F2, ≥ F3, and F4 using TE was 0.78, 0.79, and 0.96, respectively. TE performed best in children with autoimmune liver disease and in those posttransplant.

CONCLUSIONS

The present study demonstrates that TE is a reliable tool in distinguishing different stages of liver fibrosis in paediatric patients. Thus, TE may serve as a useful adjunct to liver biopsy for diagnostic purposes providing a reliable method of noninvasively monitoring liver disease progression in children.

Pediatric liver MR elastography

INTRODUCTION

Many chronic pediatric liver disorders are complicated by the development of fibrosis and ultimately cirrhosis. Although hepatic fibrogenesis progresses along a common pathway irrespective of the specific etiology, fibrosis in pediatric liver diseases has different histopathological patterns than in adults. In pediatric liver disease, as in adults, management choices may depend upon the stage of fibrosis at diagnosis. With early intervention, the progression of hepatic fibrosis can be slowed or halted, and in some situations, reversed. While liver biopsy is the gold standard for diagnosing and assessing the presence and degree of fibrosis, it has several disadvantages including the potential for sampling error, the risk of complications, the relatively high cost, and general poor acceptance by pediatric patients and their parents. MR elastography (MRE) is a relatively new imaging technique with the potential for allowing a safe, rapid, cost-effective, and non-invasive evaluation of a wide variety of hepatic diseases by quantitatively evaluating the stiffness of the liver parenchyma. The purpose of this article is to present our initial clinical experience and illustrate our modified technique for the application of liver MRE in pediatric patients at our medical center.

METHODS AND MATERIALS

Pediatric MRE techniques were developed and applied to over 45 patients scanned with our new protocol.

CONCLUSION

Liver MRE is a safe, non-invasive method for assessing hepatic fibrosis in pediatric patients.