MR and Ultrasound Elastography for Fibrosis Assessment in Children: Practical Implementation and Supporting Evidence-AJR Expert Panel Narrative Review.

Quantitative MRI and ultrasound biomarkers of liver fibrosis have become important tools in the diagnosis and clinical management of children with chronic liver disease (CLD). In particular, MR elastography (MRE) is now routinely performed in clinical practice to evaluate the liver for fibrosis. Ultrasound shear-wave elastography has also become widely performed for this purpose, especially in young children. These noninvasive methods are increasingly used to replace liver biopsy for the diagnosis, quantitative staging, and treatment monitoring of patients with CLD. Although ultrasound has advantages of portability and lower equipment cost, available evidence indicates that MRI may have greater reliability and accuracy in liver fibrosis evaluation. In this AJR Expert Panel Narrative Review, we describe how, why, and when to use MRI- and ultrasound-based elastography methods for liver fibrosis assessment in children. Practical approaches are discussed for adapting and optimizing these methods in children, with consideration of clinical indications, patient preparation, equipment requirements, acquisition technique, as well as pitfalls and confounding factors. Guidance is provided for interpretation and reporting, and representative case examples are presented.

Imaging of non-neuronopathic Gaucher disease: recent advances in quantitative imaging and comprehensive assessment of disease involvement.

Gaucher disease is an inherited metabolic disorder resulting in deficiency of lysosomal enzyme ß-glucocerebrosidase causing the accumulation of abnormal macrophages ("Gaucher cells") within multiple organs, most conspicuously affecting the liver, spleen, and bone marrow. As the most common glycolipid metabolism disorder, it is important for radiologists encountering these patients to be familiar with advances in imaging of organ and bone marrow involvement and understand the role of imaging in clinical decision-making. The recent advent of commercially available, reliable, and reproducible quantitative MRI acquisitions to measure fat fractions prompts revisiting the role of quantitative assessment of bone marrow involvement. This manuscript reviews the diverse imaging manifestations of Gaucher disease and discusses more optimal quantitative approaches to ascertain solid organ and bone marrow involvement with an emphasis on future applications of other quantitative methods including elastography.

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.

Protocol optimization for cardiac and liver iron content assessment using MRI: What sequence should I use?

OBJECTIVE: To determine the optimal MRI protocol and sequences for liver and cardiac iron estimation in children. METHODS: We evaluated patients ≤18 years with cardiac and liver MRIs for iron content estimation. Liver T2 was determined by a third-party company. Cardiac and Liver T2* values were measured by an observer. Liver T2* values were calculated using the available liver parenchyma in the cardiac MRI. Linear correlations and Bland-Altman plots were run between liver T2 and T2*, cardiac T2* values; and liver T2* on dedicated cardiac and liver MRIs. RESULTS: 139 patients were included. Mean liver T2 and T2* values were 8.6 ±â€¯5.4 ms and 4.5 ±â€¯4.1 ms, respectively. A strong correlation between liver T2 and T2* values was observed (r = 0.96, p < 0.001) with a bias (+4.1 ms). Mean cardiac bright- and dark-blood T2* values were 26.5 ±â€¯12.9 ms and 27.2 ±â€¯11.9 ms, respectively. Cardiac T2* values showed a strong correlation (r = 0.81, p < 0.001) with a low bias (-1.0 ms). The mean liver T2* on liver and cardiac MRIs were 4.9 ±â€¯4.7 ms and 4.6 ±â€¯3.9 ms, respectively. A strong correlation between T2* values was observed (r = 0.96, p < 0.001) with a small bias (-0.2 ms). CONCLUSION: MRI protocols for iron concentration in the liver and the heart can be simplified to avoid redundant information and reduce scan time. In most patients, a single breath-hold GRE sequence can be used to evaluate the iron concentration in both the liver and heart.

Prospective Assessment of Normal Pancreatic Secretory Function Measured by MRI in a Cohort of Healthy Children.

OBJECTIVES: Magnetic resonance imaging (MRI) with secretin stimulation promises to allow non-invasive testing for exocrine pancreatic insufficiency but normal data do not exist for children. The purpose of this study was to define, in healthy children, normal pancreatic secreted fluid volume and secretion rate, measured by MRI, in response to secretin. METHODS: In this Institutional Review Board-approved, prospective, cross-sectional study, 50 healthy children ages 6 to <16 years underwent MRI with secretin stimulation. Images were obtained before and at 1, 5, 10 and 15 min after secretin administration to calculate total secreted fluid volume and secretion rate based on image segmentation. Regression was used to define the relationship between secretory function and participant size measures, and linear quantile regression was used to define normal secretory values based on size measures. RESULTS: Median total secreted fluid volume post secretin was 79 mL (range: 32-162 mL; 5th and 95th percentiles: 43 and 123 mL) and median secretion rate was 5.1 mL/min (range: 2-9.4 mL/min; 5th and 95th percentiles: 2.3 and 7.7 mL/min). Secreted volume and secretion rate had the strongest correlation with body surface area (BSA) (r = 0.54 and 0.59, respectively) and multiple regression defined BSA as the only significant predictor of secretory function. Each 1 m2 increase in BSA was associated with a 38 mL increase in secreted fluid volume. CONCLUSIONS: In children, pancreatic secretory response to secretin, measured by MRI, depends on participant size, particularly BSA. Secreted volume <43 mL or a secretion rate <2.3 mL/min (5th percentile values) can be considered abnormal for children.

Spin-echo Echo-planar Imaging MR Elastography versus Gradient-echo MR Elastography for Assessment of Liver Stiffness in Children and Young Adults Suspected of Having Liver Disease.

Purpose To compare two-dimensional (2D) gradient-recalled echo (GRE) and 2D spin-echo (SE) echo-planar imaging (EPI) magnetic resonance (MR) elastography for measurement of hepatic stiffness in pediatric and young adult patients suspected of having liver disease. Materials and Methods In this institutional review board-approved, HIPAA-compliant study, 58 patients underwent both 2D GRE and 2D SE-EPI MR elastography at 1.5 T during separate breath holds. Liver stiffness (mean of means; in kilopascals) was measured by five blinded reviewers. Pooled mean liver stiffness and region-of-interest (ROI) size were compared by using paired t tests. Intraclass correlation coefficients (ICCs) were used to assess agreement between techniques. Respiratory motion artifacts were compared across sequences by using the Fisher exact test. Results Mean patient age was 14.7 years ± 5.2 (standard deviation; age range, 0.7-20.5 years), and 55.2% (32 of 58) of patients were male. Mean liver stiffness was 2.92 kPa ± 1.29 measured at GRE MR elastography and 2.76 kPa ± 1.39 at SE-EPI MR elastography (n = 290; P = .15). Mean ROI sizes were 8495 mm2 ± 4482 for 2D GRE MR elastography and 15 176 mm2 ± 7609 for 2D SE-EPI MR elastography (n = 290; P < .001). Agreement was excellent for measured stiffness between five reviewers for both 2D GRE (ICC, 0.97; 95% confidence interval: 0.95, 0.98) and 2D SE-EPI (ICC, 0.98; 95% confidence interval: 0.96, 0.99). Mean ICC (n = 5) for agreement between 2D GRE and 2D SE-EPI MR elastography was 0.93 (range, 0.91-0.95). Moderate or severe breathing artifacts were observed on 27.5% (16 of 58) of 2D GRE images versus 0% 2D SE-EPI images (P < .001). Conclusion There is excellent agreement on measured hepatic stiffness between 2D GRE and 2D SE-EPI MR elastography across multiple reviewers. SE-EPI MR elastography allowed for stiffness measurement across larger areas of the liver and can be performed in a single breath hold. © RSNA, 2016.

Brain imaging with synthetic MR in children: clinical quality assessment.

INTRODUCTION: Synthetic magnetic resonance imaging is a quantitative imaging technique that measures inherent T1-relaxation, T2-relaxation, and proton density. These inherent tissue properties allow synthesis of various imaging sequences from a single acquisition. Clinical use of synthetic MR imaging has been described in adult populations. However, use of synthetic MR imaging has not been previously reported in children. The purpose of this study is to report our assessment of diagnostic image quality using synthetic MR imaging in children. METHODS: Synthetic MR acquisition was obtained in a sample of children undergoing brain MR imaging. Image quality assessments were performed on conventional and synthetic T1-weighted, T2-weighted, and FLAIR images. Standardized linear measurements were performed on conventional and synthetic T2 images. Estimates of patient age based upon myelination patterns were also performed. RESULTS: Conventional and synthetic MR images were evaluated on 30 children. Using a 4-point assessment scale, conventional imaging performed better than synthetic imaging for T1-weighted, T2-weighted, and FLAIR images. When the assessment was simplified to a dichotomized scale, the conventional and synthetic T1-weighted and T2-weighted images performed similarly. However, the superiority of conventional FLAIR images persisted in the dichotomized assessment. There were no statistically significant differences between linear measurements made on T2-weighted images. Estimates of patient age based upon pattern of myelination were also similar between conventional and synthetic techniques. CONCLUSION: Synthetic MR imaging may be acceptable for clinical use in children. However, users should be aware of current limitations that could impact clinical utility in the software version used in this study.

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.