Hepatic magnetic resonance T1-mapping and extracellular volume fraction compared to shear-wave elastography in pediatric Fontan-associated liver disease

Quantitative Liver Imaging in Children

ABSTRACT

In children and adults, quantitative imaging examinations determine the effectiveness of treatment for liver disease. However, pediatric liver disease differs in presentation from liver disease in adults. Children also needed to be followed for a longer period from onset and have less control of their bodies, showing more movement than adults during imaging examinations, which leads to a greater need for sedation. Thus, it is essential to appropriately tailor and accurately perform noninvasive imaging tests in these younger patients. This article is an overview of updated imaging techniques used to assess liver disease quantitatively in children. The common initial imaging study for diffuse liver disease in pediatric patients is ultrasound. In addition to preexisting echo analysis, newly developed attenuation imaging techniques have been introduced to evaluate fatty liver. Ultrasound elastography is also now actively used to evaluate liver conditions, and the broad age spectrum of the pediatric population requires caution to be taken even in the selection of probes. Magnetic resonance imaging (MRI) is another important imaging tool used to evaluate liver disease despite requiring sedation or anesthesia in young children because it allows quantitative analysis with sequences such as fat analysis and MR elastography. In addition to ultrasound and MRI, we review quantitative imaging methods specifically for fatty liver, Wilson disease, biliary atresia, hepatic fibrosis, Fontan-associated liver disease, autoimmune hepatitis, sinusoidal obstruction syndrome, and the transplanted liver. Lastly, concerns such as growth and motion that need to be addressed specifically for children are summarized.

Imaging of Fontan-Associated Liver Disease

ABSTRACT

The Fontan procedure is the definitive treatment for patients with single-ventricle physiology. Surgical advances have led to a growing number of patients surviving into adulthood. Fontan-associated liver disease (FALD) encompasses a spectrum of pathologic liver changes that occur secondary to altered physiology including congestion, fibrosis, and the development of liver masses. Assessment of FALD is difficult and relies on using imaging alongside of clinical, laboratory, and pathology information. Ultrasound, computed tomography, and magnetic resonance imaging are capable of demonstrating physiologic and hepatic parenchymal abnormalities commonly seen in FALD. Several novel imaging techniques including magnetic resonance elastography are under study for use as biomarkers for FALD progression. Imaging has a central role in detection and characterization of liver masses as benign or malignant. Benign FNH-like masses are commonly encountered; however, these can display atypical features and be mistaken for hepatocellular carcinoma (HCC). Fontan patients are at elevated risk for HCC, which is a feared complication and has a poor prognosis in this population. While imaging screening for HCC is widely advocated, no consensus has been reached regarding an optimal surveillance regimen.

Significantly elevated hepatic extracellular volume in adult patients with a Fontan circulation and its correlation with impaired functional capacity

Fontan-associated liver disease is a major concern in patients who have undergone the procedure. Regular imaging of the liver is currently recommended for Fontan patients, but not other congenital heart diseases. The extracellular volume (ECV) of the liver obtained during CMR scanning and studies can show the high liver ECV in Fontan patients. However, the correlation between the liver ECV and the functional capacity of Fontan patients has not yet been reported. This study aimed to compare the liver ECV between Fontan patients and other congenital heart diseases with significant pulmonic regurgitation (PR) or tricuspid regurgitation (TR), and to evaluate the correlation between the liver ECV in adult Fontan patients and their functional capacity as well as clinical characteristics. Retrospective analysis of cardiovascular magnetic resonance imaging from patients with history of Fontan surgery between 2017 and 2021 were conducted. The clinical characteristics and liver ECV were evaluated and compared between patients and control group. Functional capacity was evaluated using a 6-min walk distance (6MWD). The correlation between the liver ECV and functional capacity was analyzed. 35 patients were enrolled in the study, including 13 Fontan patients, 12 Ebstein's anomaly or repaired tetralogy of Fallot (rTOF) patients with significant PR or TR, and 10 patients for the control group. The liver ECV were significantly higher in Fontan patients compared with Ebstein's anomaly/rTOF and the control group (41.% in Fontan group, 33.9% in Ebstein's anomaly/rTOF, and 31.7% in control group with p = 0.01 and 0.0008 in Fontan vs. Ebstein's anomaly/rTOF and Fontan vs. control group, respectively). In Fontan patients, there was a significant correlation between the liver ECV and the liver blood biochemistry with r = 0.879, p = 0.01 for AST/ALT ratio and r = 0.65, p = 0.005 for AST. The liver ECV was inversely correlated with the six-minute walk distance (r = -0.55, p = 0.02). The liver ECV in patients who had undergone Fontan operation showed a significantly elevated and has significantly inversed correlation with their functional capacity. These findings indicated that the liver ECV may be a potentialmarker for adverse clinical outcomes. However, due to small size population, further prospective study with larger number of patients may validate this findings.

Liver T1/T2 values with cardiac MRI during respiration

BACKGROUND

Assessing the hepatic status of children with CHD is very important in the post-operative period. This study aimed to assess the usefulness of paediatric liver T1/T2 values and to evaluate the impact of respiration on liver T1/T2 values.

METHODS

Liver T1/T2 values were evaluated in 69 individuals who underwent cardiac MRI. The mean age of the participants was 16.2 ± 9.8 years. Two types of imaging with different breathing methods were possible in 34 participants for liver T1 values and 10 participants for liver T2 values.

RESULTS

The normal range was set at 620-830 msec for liver T1 and 25-40 ms for liver T2 based on the data obtained from 17 healthy individuals. The liver T1/T2 values were not significantly different between breath-hold and free-breath imaging (T1: 769.4 ± 102.8 ms versus 763.2 ± 93.9 ms; p = 0.148, T2: 34.9 ± 4.0 ms versus 33.6 ± 2.4 ms; p = 0.169). Higher liver T1 values were observed in patients who had undergone Fontan operation, tetralogy of Fallot operation, or those with chronic viral hepatitis. There was a trend toward correlation between liver T1 values and liver stiffness (R = 0.65, p = 0.0004); and the liver T1 values showed a positive correlation with the shear wave velocity (R = 0.62, p = 0.0006).

CONCLUSIONS

Liver T1/T2 values were not affected by breathing patterns. Because liver T1 values tend to increase with right heart overload, evaluation of liver T1 values during routine cardiac MRI may enable early detection of future complications.

Normal Ventricular and Regional Blood Flow Volumes and Native T1 Values in Healthy Japanese Children Obtained from Comprehensive Cardiovascular Magnetic Resonance Imaging

Age-related mean and reference ranges for ventricular volumes and mass, regional blood flow measurements, and T1 values using cardiovascular magnetic resonance (CMR) imaging are yet to be established for the pediatric population. Especially in infants and toddlers, no consistent flow volume sets or T1 values have been reported. The purpose of this study was to determine the relevant normal values.Twenty-three children (aged 0.1-15.3 years) without cardiovascular diseases were included. Comprehensive CMR imaging including cine, 2-dimensional phase-contrast, and native T1 mapping, were performed. Ventricular volumes and masses, 11 sets of regional blood flow volumes, and myocardial and liver T1 values were measured. All intraclass correlation coefficient values were > 0.94, except for the right ventricular mass (0.744), myocardial (0.868) and liver T1 values (0.895), reflecting good to excellent agreement between rates.Regression analysis showed an exponential relationship between body surface area (BSA) and ventricular volumes, mass, and regional blood flow volumes (normal value = a*BSAb). Left ventricular myocardial T1 values were regressed on linear regression with age (normal value = -7.39*age + 1091), and hepatic T1 values were regressed on a quadratic function of age (normal value = 0.923*age2 -18.012*age + 613).Comparison of the 2 different methods for the same physical quantities by Bland-Altman plot showed no difference except that the right ventricular stroke volume was 1.5 mL larger than the main pulmonary trunk flow volume.This study provides the normal values for comprehensive CMR imaging in Japanese children.

Fontan-associated liver disease: Diagnosis, surveillance, and management

The Fontan operation is a lifesaving procedure for patients with functional single-ventricle congenital heart disease, where hypoplastic left heart syndrome is the most frequent anomaly. Hemodynamic changes following Fontan circulation creation are now increasingly recognized to cause multiorgan affection, where the development of a chronic liver disease, Fontan-associated liver disease (FALD), is one of the most important morbidities. Virtually, all patients with a Fontan circulation develop liver congestion, resulting in fibrosis and cirrhosis, and most patients experience childhood onset. FALD is a distinctive type of congestive hepatopathy, and its pathogenesis is thought to be a multifactorial process driven by increased nonpulsatile central venous pressure and decreased cardiac output, both of which are inherent in the Fontan circulation. In the advanced stage of liver injury, complications of portal hypertension often occur, and there is a risk of developing secondary liver cancer, reported at young age. However, FALD develops with few clinical symptoms, a surprisingly variable degree of severity in liver disease, and with little relation to poor cardiac function. The disease mechanisms and modifying factors of its development are still not fully understood. As one of the more important noncardiac complications of the Fontan circulation, FALD needs to be diagnosed in a timely manner with a structured monitoring scheme of disease development, early detection of malignancy, and determination of the optimal time point for transplantation. There is also a clear need for consensus on the best surveillance strategy for FALD. In this regard, imaging plays an important role together with clinical scoring systems, biochemical workups, and histology. Patients operated on with a Fontan circulation are generally followed up in cardiology units. Ultimately, the resulting multiorgan affection requires a multidisciplinary team of healthcare personnel to address the different organ complications. This article discusses the current concepts, diagnosis, and management of FALD, with special emphasis on the role of different imaging techniques in the diagnosis and monitoring of disease progression, as well as current recommendations for liver disease surveillance.

Quantitative abdominal magnetic resonance imaging in children-special considerations

The use of quantitative MRI methods for assessment of the abdomen in children has become commonplace over the past decade. Increasingly employed methods include MR elastography, chemical shift encoded (CSE) MR imaging for determination of proton density fat fraction, diffusion-weighted imaging, and a variety of relaxometry techniques, such as T1 and T2* mapping. These techniques can be used in a variety of settings to distinguish normal from abnormal tissue as well as determine the severity of disease. The performance of quantitative MRI methods in the pediatric population presents unique challenges as compared to adult populations. These challenges relate to multiple factors, including patient size, pediatric physiology, inability to breath hold, and greater physical motion during the examination. The purpose of this review article is to review quantitative MRI methods that may be used in clinical practice to assess the pediatric abdomen and to discuss special considerations when performing these techniques in children.

Efficacy Analysis of Double-Low Dynamic Contrast-Enhanced CT and Hepatic Extracellular Volume Fraction in the Diagnosis of Liver Fibrosis

Objective

The aim of the study was to analyze the efficacy of double-low dynamic contrast-enhanced CT (DCE-CT) and hepatic extracellular volume fraction (fECV) in the diagnosis of liver fibrosis (LF).

Methods

A total of 200 patients with LF and cirrhosis who underwent the histopathological examination of liver biopsy and multiphase DCE-CT of the liver at the same time in our hospital (January 2020–December 2020) were selected as the research subjects, and the degree of liver fibrosis was staged according to pathological criteria to analyze the clinical diagnostic value of double-low DCE-CT and fECV.

Results

Compared with the S2–S4 group, the S1 group had obviously higher Eaorta and HCT values (P < 0.05), a lower fECV value (P < 0.001), and lower serum IVC and LN levels (P < 0.001). Serum IVC and LN levels were positively correlated with fECV (r₁ = 0.803 and r₂ = 0.890; P < 0.001). The fECV had the highest specificity and negative predictive value in the diagnosis of S1 and had the highest sensitivity and positive predictive value in the diagnosis of S2–S4.

Conclusion

The double-low DCE-CT and fECV can provide a reliable basis for the clinical diagnosis of LF, and their results will provide a new direction for the treatment of LF and have a high application value in the clinical practice.

Effect of Iron Deposition on Native T1 Mapping and Blood Oxygen Level Dependent for the Assessment of Liver Fibrosis in Rabbits With Carbon Tetrachloride Intoxication

RATIONALE AND OBJECTIVES

This study aimed to explore the effect of iron deposition on native T1 mapping and blood oxygen level-dependent (BOLD) imaging in detecting liver fibrosis (LF) in a rabbit model.

MATERIALS AND METHODS

An LF group (n = 100) was established by subcutaneously injecting 50% carbon tetrachloride (CCl₄) oil solution, and 20 normal rabbits composed a control group. Native T1 mapping and BOLD were performed, and the T1_native and R₂* quantitative parameters were analyzed by receiver operating characteristic (ROC) and multiple logistic regression analyses, with histopathological results and liver iron content (LIC) serving as reference standards.

RESULTS

In total, 18, 17, 16, 18, and 15 rabbits were histopathologically diagnosed with LF stages F0, F1, F2, F3, and F4, respectively. T1_native (r = 0.47), R₂* (r = 0.75) and LIC (r = 0.61) increased with LF stage progression (p < 0.001). Compared to T1_native values, R₂* performed better in diagnosing the LF stage, especially for distinguishing F1-F2 from F3-F4 (AUC = 0.66 vs. 0.91, p = 0.01). Combined with the LIC, both T1_native and R₂* showed improved diagnostic value in comparison to the individual imaging techniques, particularly for diagnosing F0 vs. F1-F2 and F0 vs. F1-F4, with AUC values of 0.90 vs. 0.70 (p = 0.01) and 0.93 vs. 0.77 (p = 0.01) for T1_native + LIC vs. LIC, respectively.

CONCLUSION

BOLD imaging performed better than native T1 mapping in predicting and diagnosing LF stage progression. The decrease in diagnostic accuracy caused by the deposition of liver iron is a potential pitfall in the assessment of LF with BOLD imaging and native T1 mapping.

4D flow cardiovascular magnetic resonance derived energetics in the Fontan circulation correlate with exercise capacity and CMR-derived liver fibrosis/congestion

AIM

This study explores the relationship between in vivo 4D flow cardiovascular magnetic resonance (CMR) derived blood flow energetics in the total cavopulmonary connection (TCPC), exercise capacity and CMR-derived liver fibrosis/congestion.

BACKGROUND

The Fontan circulation, in which both caval veins are directly connected with the pulmonary arteries (i.e. the TCPC) is the palliative approach for single ventricle patients. Blood flow efficiency in the TCPC has been associated with exercise capacity and liver fibrosis using computational fluid dynamic modelling. 4D flow CMR allows for assessment of in vivo blood flow energetics, including kinetic energy (KE) and viscous energy loss rate (EL).

METHODS

Fontan patients were prospectively evaluated between 2018 and 2021 using a comprehensive cardiovascular and liver CMR protocol, including 4D flow imaging of the TCPC. Peak oxygen consumption (VO2) was determined using cardiopulmonary exercise testing (CPET). Iron-corrected whole liver T1 (cT1) mapping was performed as a marker of liver fibrosis/congestion. KE and EL in the TCPC were computed from 4D flow CMR and normalized for inflow. Furthermore, blood flow energetics were compared between standardized segments of the TCPC.

RESULTS

Sixty-two Fontan patients were included (53% male, 17.3 ± 5.1 years). Maximal effort CPET was obtained in 50 patients (peak VO2 27.1 ± 6.2 ml/kg/min, 56 ± 12% of predicted). Both KE and EL in the entire TCPC (n = 28) were significantly correlated with cT1 (r = 0.50, p = 0.006 and r = 0.39, p = 0.04, respectively), peak VO2 (r = - 0.61, p = 0.003 and r = - 0.54, p = 0.009, respectively) and % predicted peak VO2 (r = - 0.44, p = 0.04 and r = - 0.46, p = 0.03, respectively). Segmental analysis indicated that the most adverse flow energetics were found in the Fontan tunnel and left pulmonary artery.

CONCLUSIONS

Adverse 4D flow CMR derived KE and EL in the TCPC correlate with decreased exercise capacity and increased levels of liver fibrosis/congestion. 4D flow CMR is promising as a non-invasive screening tool for identification of patients with adverse TCPC flow efficiency.

Non-contrast enhanced magnetic resonance imaging for characterization of Fontan associated liver disease

OBJECTIVES

To evaluate the ability of non-contrast enhanced magnetic resonance imaging (MRI) techniques to characterize Fontan associated liver disease (FALD) in adolescent and adult Fontan patients.

METHODS

Fontan patients (n = 29) and healthy controls (n = 13) underwent an MRI protocol with T₁, T₂ and Apparent Diffusion Coefficient (ADC) mapping. Routine FALD screening included abdominal ultrasound and laboratory testing.

RESULTS

Median follow-up after Fontan operation was 15.1 (IQR 12.0-16.8) years. Distinct differences in tissue characteristics were visualized. T₁ and T₂ relaxation times were prolonged in Fontan patients, particularly of the right lobe (T₁: 745 (IQR 715-784) ms vs. 586 (IQR 555-602) ms, p < 0.001; T₂: 63 (IQR 59-64) ms vs. 58 (IQR 56-60) ms, p = 0.002). Left lobe ADC was lower in Fontan patients (1.10 (IQR 1.06-1.18) x 10^-3 mm²/s vs. 1.23 (IQR 1.19-1.29) x 10^-3 mm²/s, p < 0.001). T₂ mapping was able to differentiate between controls and Fontan patients with different FALD severity. Right lobe T₂ was higher in patients with moderate or severe in comparison to those with no or mild changes and healthy controls (64 (IQR 61-67) ms vs. 60 (IQR 59-63) ms vs. 58 (IQR 56-60) ms, p = 0.001).

CONCLUSIONS

Non-contrast enhanced MRI methods are able to visualize regional differences in liver tissue characteristics. T₁ and T₂ relaxation times were prolonged in Fontan patients suggestive of fibrosis or congestive hepatopathy, while reduced ADC might reflect impaired microperfusion. These methods have promising clinical potential for detection of liver abnormalities in Fontan patients. The usefulness of T₂ mapping to grade FALD severity merits further investigation.

Spectrum of Fontan-associated liver disease assessed by MRI and US in young adolescents

Purpose

Patients with Fontan circulation are at risk of developing hepatic fibrosis/cirrhosis. The mechanisms and disease development are unclear and early secondary liver cancer is a concern. This study will describe hepatic imaging findings in a national cohort of adolescents with Fontan circulation.

Methods

The patients prospectively underwent abdominal contrast enhanced magnetic resonance imaging (MRI) including diffusion-weighted imaging. Images were assessed for criteria of fibrosis/cirrhosis including characterization of hepatic nodules. These nodules were in addition, assessed by ultrasonography (US). Nodules ≥ 1 cm were investigated and monitored to evaluate malignant transformation. Clinical and hepatic serological data were recorded.

Results

Forty-six patients, median age of 16.5 years (15.4–17.9 years) were enrolled. All patients underwent US examination and MRI was performed in 35/46 patients. On MRI, 60% had hepatomegaly and 37% had signs of fibrosis/cirrhosis. Seven patients had together 13 nodules ≥ 1 cm in diameter. Only 4/13 (17%) where seen on US. Nodules had variable MRI signal characteristics including hepatobiliary contrast enhancement and two nodules revealed portal venous phase ‘wash-out’ on the first examination. No further imaging signs of malignancy were revealed during the follow-up period of median 24.4 (7–42) months.

Conclusion

The majority of adolescents with Fontan circulation had imaging findings of fibrosis/cirrhosis of varying severity. US had low detection rate of hepatic nodules compared to MRI. The imaging work-up before transition to adult cardiology care did not reveal findings suggestive of malignancy. However, the high prevalence of Fontan-associated liver disease calls for surveillance strategies even in childhood.

Supplementary Information

The online version of this article (10.1007/s00261-021-02994-0) contains supplementary material, which is available to authorized users.