Elastography to assess the stage of liver fibrosis in children: Concepts, opportunities, and challenges

T1 Mapping of the Abdomen, From the AJR "How We Do It" Special Series

By exploiting different tissues' characteristic T1 relaxation times, T1-weighted images help distinguish normal and abnormal tissues, aiding assessment of diffuse and local pathologies. However, such images do not provide quantitative T1 values. Advances in abdominal MRI techniques have enabled measurement of abdominal organs' T1 relaxation times, which can be used to create color-coded quantitative maps. T1 mapping is sensitive to tissue microenvironments including inflammation and fibrosis and has received substantial interest for noninvasive imaging of abdominal organ pathology. In particular, quantitative mapping provides a powerful tool for evaluation of diffuse disease by making apparent changes in T1 occurring across organs that may otherwise be difficult to identify. Quantitative measurement also facilitates sensitive monitoring of longitudinal T1 changes. Increased T1 in liver helps to predict parenchymal fibro-inflammation, in pancreas is associated with reduced exocrine function from chronic or autoimmune pancreatitis, and in kidney is associated with impaired renal function and aids diagnosis of chronic kidney disease. In this review, we describe the acquisition, postprocessing, and analysis of T1 maps in the abdomen and explore applications in liver, spleen, pancreas, and kidney. We highlight practical aspects of implementation and standardization, technical pitfalls and confounding factors, and areas of likely greatest clinical impact.

Technical Success and Reliability of Magnetic Resonance Elastography in Patients with Hepatic Iron Overload

RATIONALE AND OBJECTIVES

This study aimed to evaluate the technical success rate and stiffness measurement reliability of two specific hepatic magnetic resonance elastography (MRE) sequences dedicated to solving susceptibility artifacts in patients with various degrees of hepatic iron overload.

MATERIALS AND METHODS

Thirty-seven patients with iron-overloaded liver confirmed by R2* value measurement who underwent two-dimensional (2D) spin-echo (SE) MRE and 2D SE-echo-planar-imaging (EPI) MRE were reviewed retrospectively. According to four categories based on R2* value (mild, moderate, severe elevation, and extremely severe iron overload), we compared the success rate, quality score, and liver stiffness of the two sequences. In addition, Spearman's correlation was performed to evaluate the relationship between the R2* value and liver stiffness.

RESULTS

The overall success rates of SE MRE and SE-EPI MRE in patients with hepatic iron overload were 91.89% and 78.38%, respectively, and 100% and 78.57%, respectively, for severe elevation iron overload. In all patients, the MRE quality scores were 54 and 48 for SE MRE and SE-EPI MRE, respectively (P = 0.107). There were no significant differences in liver stiffness measurements between the two MRE methods in patients with mild, moderate, and severe elevation iron-overloaded livers (P > 0.6 for all), respectively. For both MRE methods, R2* value had no significant effect on the liver stiffness measurements (correlation coefficient <0.1, P >0.6 for both).

CONCLUSION

In the mild and moderate elevation iron-overloaded liver, both SE MRE and fast SE-EPI MRE can provide successful and reliable liver stiffness measurement. In severe elevation iron-overloaded livers, SE MRE may be a better choice than SE-EPI MRE.

Liver fibrosis assessment in pediatric population - can ultrasound elastography be an alternative method to liver biopsy? A systematic review

Liver diseases of various etiologies are becoming increasingly common in the pediatric population. So far, the gold diagnostic standard in these disorders is liver biopsy. This procedure is invasive, painful and requires general anesthesia in this group of patients. Due to the continuous development of new research techniques, such as liver elastography, it is necessary to evaluate them in the context of their diagnostic usefulness. Ultrasound elastography, as a quick and effective method, is being used more and more often in the assessment and monitoring of liver dysfunction in both adults and children. There are several techniques of liver elastography, such as transient elastography, shear wave elastography consisting of various subtypes such as two-dimensional shear wave elastography, acoustic radiation force impulse and point shear wave elastography, which differ in terms of the measurement technique and the achieved results. The purpose of our review was to determine whether techniques of liver elastography could replace liver biopsy. Although now, based on the analyzed papers, elastography cannot replace liver biopsy, in our opinion, the role of this tool in monitoring pediatric patients with liver diseases will grow in the coming years.

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.

Associations of Liver Stiffness Measured by Ultrasound Shear-Wave Elastography With Portal Hypertension and Circulatory Failure in Individuals With Fontan Circulation

BACKGROUND. The Fontan operation palliates single-ventricle congenital heart disease but causes hepatic congestion with associated progressive hepatic fibrosis. OBJECTIVE. The purpose of this study was to evaluate associations between liver stiffness measured using ultrasound (US) shear-wave elastography (SWE) in patients with Fontan palliation and the occurrence of portal hypertension and Fontan circulatory failure during follow-up. METHODS. This retrospective study included 119 individuals 10 years old or older (median age, 19.1 years; 61 female patients, 58 male patients) with Fontan circulation who underwent liver US with 2D SWE from January 1, 2015, to January 1, 2022, and had 1 year or more of clinical follow-up (unless experiencing earlier outcome-related events). Median liver stiffness from the initial US examination was documented. Varices, ascites, splenomegaly, and thrombocytopenia (VAST) scores (range, 0-4) were determined as a marker of portal hypertension on initial US examination and 1 year or more of follow-up imaging (US, CT, or MRI). Composite clinical outcome for Fontan circulatory failure (death, mechanical circulatory support, cardiac transplant, or unexpected Fontan circulation-related hospitalization) was assessed. Analysis included the Wilcoxon rank sum test, logistic regression analysis with stepwise variable selection, and ROC analysis. RESULTS. Median initial liver stiffness was 2.22 m/s. Median initial VAST score was 0 (IQR, 0-1); median follow-up VAST score was 1 (IQR, 0-2) (p = .004). Fontan circulatory failure occurred in 37 of 119 (31%) patients (median follow-up, 3.4 years). Initial liver stiffness was higher in patients with a follow-up VAST score of 1 or greater (2.37 m/s) than in those with a follow-up VAST score of 0 (2.08 m/s) (p = .005), and initial liver stiffness was higher in patients with (2.43 m/s) than without (2.10 m/s) Fontan circulatory failure during follow-up (p < .001). Initial liver stiffness was the only significant independent predictor of Fontan circulatory failure (OR = 3.76; p < .001); age, sex, Fontan operation type, dominant ventricular morphology, and initial VAST score were not independent predictors. Initial liver stiffness had an AUC of 0.70 (sensitivity, 79%; specificity, 57%; threshold, > 2.11 m/s) for predicting a follow-up VAST score of 1 or greater and an AUC of 0.74 (sensitivity, 84%; specificity, 52%; threshold, > 2.12 m/s) for predicting Fontan circulatory failure. CONCLUSION. In patients with Fontan circulation, increased initial liver stiffness was associated with portal hypertension and circulatory failure during follow-up, although it had moderate performance in predicting these outcomes. CLINICAL IMPACT. US SWE may play a role in post-Fontan surveillance, supporting tailored medical and surgical care.

Liver cirrhosis in children - the role of imaging in the diagnostic pathway

Liver cirrhosis in children is a rare disease with multifactorial causes that are distinct from those in adults. Underlying reasons include cholestatic, viral, autoimmune, hereditary, metabolic and cardiac disorders. Early detection of fibrosis is important as clinical stabilization or even reversal of fibrosis can be achieved in some disorders with adequate treatment. This article focuses on the longitudinal evaluation of children with chronic liver disease with noninvasive imaging tools, which play an important role in detecting cirrhosis, defining underlying causes, grading fibrosis and monitoring patients during follow-up. Ultrasound is the primary imaging modality and it is used in a multiparametric fashion. Magnetic resonance imaging and computed tomography are usually applied second line for refined tissue characterization, clarification of nodular lesions and full delineation of abdominal vessels, including portosystemic communications.

Liver and spleen volume and stiffness in patients post-Fontan procedure and patients with ARPKD compared to normal controls

PURPOSE

Both congestive (patients post-Fontan hepatopathy) and congenital (patients with ARPKD) disease can lead to hepatic fibrosis and portal hypertension with eventual development of splenomegaly. We investigated liver and spleen stiffness as measured by MRE between post-Fontan, ARPKD patients and controls independent of organ volume.

METHODS

Our study included 122 subjects (70 Fontan patients, 14 ARPKD patients, and 38 controls). The mean MRE liver and spleen stiffness values of Fontan patients and patients with ARPKD were compared to controls. Similarly, the liver and spleen volumes of the Fontan patients and patients with ARPKD were then compared to the volumes of controls.

RESULTS

Post-Fontan and ARPKD patients, mean liver stiffness, mean liver volume as well as mean spleen stiffness and mean spleen volume were higher than mean liver stiffness, mean liver volume, mean spleen stiffness, and mean spleen volume of controls. While liver stiffness correlated to liver volume in controls, we found no correlation between stiffness and volume in either Fontan or ARPKD patients, which indicates MRE's ability to act as an independent biomarker. However, these findings are not true in the spleen, where there is significant association between volume and stiffness in patients with ARPKD, but not in Fontan patients or controls.

CONCLUSION

Liver and spleen stiffness and volumes are significantly different among Fontan patients, ARPKD patients, and controls. Our findings suggest that beyond diagnosing fibrosis, MRE cut-off values could be disease-specific since not only the severity but the underlying pathology causing organ congestion or fibrosis influences MRE results.

Basics of magnetic resonance imaging and quantitative parameters T1, T2, T2*, T1rho and diffusion-weighted imaging

Magnetic resonance imaging is widely available and accepted as the imaging method of choice for many pediatric body imaging applications. Traditionally, it has been used in a qualitative way, where the images are reported non-numerically by radiologists. But now MRI machines have built-in post-processing software connected to the scanner and the database of MR images. This setting enables and encourages simple quantitative analysis of MR images. In this paper, the author reviews the fundamentals of MRI and discusses the most common quantitative MRI techniques for body imaging: T1, T2, T2*, T1rho and diffusion-weighted imaging (DWI). For each quantitative imaging method, this article reviews the technique, its measurement mechanism, and selected clinical applications to body imaging.

Machine Learning Evaluation of Biliary Atresia Patients to Predict Long-Term Outcome after the Kasai Procedure

Kasai portoenterostomy (KP) represents the first-line treatment for biliary atresia (BA). The purpose was to compare the accuracy of quantitative parameters extracted from laboratory tests, US imaging, and MR imaging studies using machine learning (ML) algorithms to predict the long-term medical outcome in native liver survivor BA patients after KP. Twenty-four patients were evaluated according to clinical and laboratory data at initial evaluation (median follow-up = 9.7 years) after KP as having ideal (n = 15) or non-ideal (n = 9) medical outcomes. Patients were re-evaluated after an additional 4 years and classified in group 1 (n = 12) as stable and group 2 (n = 12) as non-stable in the disease course. Laboratory and quantitative imaging parameters were merged to test ML algorithms. Total and direct bilirubin (TB and DB), as laboratory parameters, and US stiffness, as an imaging parameter, were the only statistically significant parameters between the groups. The best algorithm in terms of accuracy, sensitivity, specificity, and AUCROC was naive Bayes algorithm, selecting only laboratory parameters (TB and DB). This preliminary ML analysis confirms the fundamental role of TB and DB values in predicting the long-term medical outcome for BA patients after KP, even though their values may be within the normal range. Physicians should be alert when TB and DB values change slightly.

What is the impact of methotrexate on liver in patients with juvenile idiopathic arthritis? Results of liver SWE performed in a single centre

OBJECTIVES

Long-term therapy with low-dose methotrexate (MTX) is widely used in treatment of rheumatic diseases, in children. The purpose of this study was to evaluate liver elasticity in patients with juvenile idiopathic arthritis (JIA) who received MTX and compare the results with control group.

METHODS

Liver elasticity was evaluated with shear wave elastography (SWE) technique in 25 patients aged 3-17 years who were followed up with JIA and received MTX and compared with 25 healthy controls of the same age and weight. Factors that had an effect on liver elasticity were examined.

RESULTS

The mean SWE value of patients was 2.64 ± 2.13 m/s and 24.10 ± 18.50 kPa, whereas 1.83 ± 0.16 m/s and 10.09 ± 1.83 kPa in control group. There was a significant difference in liver elasticity in the patient and control groups. When the patients were evaluated as Group 1 (< 1000 mg) and Group 2 (≥ 1000 mg) according to the cumulative MTX dose, no significant difference was obtained. There was positive correlation between liver elasticity and weekly MTX dose and age.

CONCLUSIONS

Our study revealed that liver elasticity significantly decreased in patients who received MTX when compared with the control group. The elastography technique will be understood better over time and used safely in many areas.

Imaging prediction with ultrasound and MRI of long-term medical outcome in native liver survivor patients with biliary atresia after kasai portoenterostomy: a pilot study

PURPOSE

To comparatively assess the role of abdominal ultrasound (US) and magnetic resonance imaging (MRI) in predicting long-term medical outcome in native liver survivor patients with biliary atresia (BA) after Kasai portoenterostomy (KP).

METHODS

Twenty-four retrospectively enrolled patients were divided in two groups according to clinical and laboratory data at initial evaluation after KP (median follow-up = 9.7 years; range = 5-25 years) as with ideal (Group 1; n = 15) or non-ideal (Group 2; n = 9) medical outcome. All patients were re-evaluated for a period of additional 4 years using clinical and laboratory indices. US and MRI studies were qualitatively analyzed assessing imaging signs suggestive of chronic liver disease (CLD).

RESULTS

At re-evaluation, 6 patients (40%) of Group 1 changed their medical outcome in non-ideal (Group 1A); the other 9 patients (60%) remained stable (Group 1B); the mean time to change the medical outcome in non-ideal status at re-evaluation was 43.5 ± 2.3 months. The area under the ROC curve was 0.84 and 0.87 for US and MRI scores to predict long-term medical outcome with the best cut-off value score > 4 for both modalities (p = 0.89). In Group 2, 6 (67%) patients showed a clinical progression (Group 2A) with a mean time of 39.8 ± 3.8 months; in the other 3 (33%) patients, no clinical progression was observed (Group 2B).

CONCLUSION

In BA patients with ideal medical outcome after KP, US and MRI may both predict long-term outcome. US, non-invasive and widely available technique, should be preferred.

The evaluation of the use of 2D shear-wave ultrasound elastography in differentiation of clinically insignificant and significant liver fibrosis in pediatric age group

OBJECTIVE

To determine the accuracy of 2D shear-wave elastography (2D-SWE) in pediatric age group patients in differentiating clinically insignificant and significant liver fibrosis using METAVIR fibrosis scoring system as the gold standard.

INTRODUCTION

Liver biopsy has long been the gold standard in liver fibrosis diagnosis. However, due to probable complications and sampling variabilities, the need for more accurate and non-invasive techniques has increased. 2D-SWE is a non-invasive technique used in the evaluation of liver stiffness and utilized more and more in routine clinical practice with recent advances and researches.

MATERIALS AND METHODS

In this retrospective single-center study, we included 46 pediatric age group patients who had a liver parenchymal biopsy and 2D-SWE evaluation regardless of etiology. For 2D-SWE, the LOGIQ E9 system (GE Medical Systems, Wisconsin, USA) and, for histopathological evaluation, METAVIR fibrosis scoring system were utilized. Patients were further subgrouped as clinically insignificant (METAVIR Score F0-1) and significant (METAVIR Score F2-4). The Kolmogorov-Smirnov and Mann-Whitney U tests were employed for statistical analysis. The diagnostic accuracy of 2D-SWE was assessed, and cutoff values were set by ROC curve analysis.

RESULTS

kPa values were statistically different between clinically significant and insignificant fibrosis patient groups (p < 0.001). kPa value of 8.92 was designated as the best cutoff value according to the Youden Index.

CONCLUSION

2D-SWE is one of the non-invasive techniques in the evaluation of liver fibrosis. Our findings suggest that 2D-SWE accurately differentiate clinically insignificant and significant liver fibrosis.

Microscope-Based Automated Quantification of Liver Fibrosis in Mice Using a Deep Learning Algorithm

In preclinical studies that involve animal models for hepatic fibrosis, accurate quantification of the fibrosis is of utmost importance. The use of digital image analysis based on deep learning artificial intelligence (AI) algorithms can facilitate accurate evaluation of liver fibrosis in these models. In the present study, we compared the quantitative evaluation of collagen proportionate area in the carbon tetrachloride model of liver fibrosis in the mouse by a newly developed AI algorithm to the semiquantitative assessment of liver fibrosis performed by a board-certified toxicologic pathologist. We found an excellent correlation between the 2 methods of assessment, most evident in the higher magnification (×40) as compared to the lower magnification (×10). These findings strengthen the confidence of using digital tools in the toxicologic pathology field as an adjunct to an expert toxicologic pathologist.

Magnetic resonance elastography to quantify liver disease severity in autosomal recessive polycystic kidney disease

OBJECTIVES

To evaluate whether liver and spleen magnetic resonance elastography (MRE) can measure the severity of congenital hepatic fibrosis (CHF) and portal hypertension (pHTN) in individuals with autosomal recessive polycystic kidney disease (ARPKD), and to examine correlations between liver MRE and ultrasound (US) elastography.

METHODS

Cross-sectional study of nine individuals with ARPKD and 14 healthy controls. MRE was performed to measure mean liver and spleen stiffness (kPa); US elastography was performed to measure point shear wave speed (SWS) in both liver lobes. We compared: (1) MRE liver and spleen stiffness between controls vs. ARPKD; and (2) MRE liver stiffness between participants with ARPKD without vs. with pHTN, and examined correlations between MRE liver stiffness, spleen length, platelet counts, and US elastography SWS. Receiver operating characteristic (ROC) analysis was performed to examine diagnostic accuracy of liver MRE.

RESULTS

Participants with ARPKD (median age 16.8 [IQR 13.3, 18.9] years) had higher median MRE liver stiffness than controls (median age 14.7 [IQR 9.7, 16.7 years) (2.55 vs. 1.92 kPa, p = 0.008), but MRE spleen stiffness did not differ. ARPKD participants with pHTN had higher median MRE liver stiffness than those without (3.60 kPa vs 2.49 kPa, p = 0.05). Liver MRE and US elastography measurements were strongly correlated. To distinguish ARPKD vs. control groups, liver MRE had 78% sensitivity and 93% specificity at a proposed cut-off of 2.48 kPa [ROC area 0.83 (95% CI 0.63-1.00)].

CONCLUSION

Liver MRE may be a useful quantitative method to measure the severity of CHF and pHTN in individuals with ARPKD.

MR Elastography of the Abdomen: Basic Concepts

Magnetic resonance elastography (MRE) is an emerging imaging modality that maps the elastic properties of tissue such as the shear modulus. It allows for noninvasive assessment of stiffness, which is a surrogate for fibrosis. MRE has been shown to accurately distinguish absent or low stage fibrosis from high stage fibrosis, primarily in the liver. Like other elasticity imaging modalities, it follows the general steps of elastography: (1) apply a known cyclic mechanical vibration to the tissue; (2) measure the internal tissue displacements caused by the mechanical wave using magnetic resonance phase encoding method; and (3) infer the mechanical properties from the measured mechanical response (displacement), by generating a simplified displacement map. The generated map is called an elastogram.While the key interest of MRE has traditionally been in its application to liver, where in humans it is FDA approved and commercially available for clinical use to noninvasively assess degree of fibrosis, this is an area of active research and there are novel upcoming applications in brain, kidney, pancreas, spleen, heart, lungs, and so on. A detailed review of all the efforts is beyond the scope of this chapter, but a few specific examples are provided. Recent application of MRE for noninvasive evaluation of renal fibrosis has great potential for noninvasive assessment in patients with chronic kidney diseases. Development and applications of MRE in preclinical models is necessary primarily to validate the measurement against "gold-standard" invasive methods, to better understand physiology and pathophysiology, and to evaluate novel interventions. Application of MRE acquisitions in preclinical settings involves challenges in terms of available hardware, logistics, and data acquisition. This chapter will introduce the concepts of MRE and provide some illustrative applications.This publication is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This introduction chapter is complemented by another separate chapter describing the experimental protocol and data analysis.

Ultrasound, shear-wave elastography, and magnetic resonance imaging in native liver survivor patients with biliary atresia after Kasai portoenterostomy: correlation with medical outcome after treatment

BACKGROUND

Biliary atresia (BA) is a rare obliterative cholangiopathy and Kasai portoenterostomy (KP) represents its first-line treatment; clinical and laboratory parameters together with abdominal ultrasound (US) are usually performed during the follow-up. Shear-wave elastography (SWE) is able to evaluate liver parenchyma stiffness; magnetic resonance imaging (MRI) has also been proposed to study these patients.

PURPOSE

To correlate US, SWE, and MRI imaging findings with medical outcome in patients with BA who are native liver survivors after KP.

MATERIAL AND METHODS

We retrospectively enrolled 24 patients. They were divided in two groups based on "ideal" (n = 15) or "non-ideal" (n = 9) medical outcome. US, SWE, and MRI exams were analyzed qualitatively and quantitatively for imaging signs suggestive of chronic liver disease (CLD).

RESULTS

Significant differences were found in terms of liver surface (P = 0.007) and morphology (P = 0.013), portal vein diameter (P = 0.012) and spleen size (P = 0.002) by US, liver signal intensity (P = 0.013), portal vein diameter (P = 0.010), presence of portosystemic collaterals (P = 0.042), and spleen size (P = 0.001) by MRI. The evaluation of portal vein diameter (moderate, κ = 0.44), of portosystemic collaterals (good, κ = 0.78), and spleen size (very good, κ = 0.92) showed the best agreement between US and MRI. A significant (P = 0.01) difference in liver parenchyma stiffness by SWE was also found between the two groups (cut-off = 9.6 kPa, sensitivity = 55.6%, specificity = 100%, area under the ROC curve = 0.82).

CONCLUSION

US, SWE, and MRI findings correlate with the medical outcome in native liver survivor patients with BA treated with KP.

Comparison of liver T1 relaxation times without and with iron correction in pediatric autoimmune liver disease

BACKGROUND

Magnetic resonance imaging (MRI) T1 relaxometry (mapping) has been reported as a quantitative biomarker of liver injury due to inflammation and fibrosis.

OBJECTIVE

To assess the relationship between liver MRI T1 relaxometry measurements obtained using a modified Look-Locker inversion recovery (MOLLI) pulse sequence without and with iron (T2*) correction (cT1) in pediatric autoimmune liver disease.

MATERIALS AND METHODS

This cross-sectional study was institutional review board-approved, with informed consent obtained. MRI was acquired at 1.5 T in patients participating in an autoimmune liver disease registry. T1 relaxometry was performed using a MOLLI sequence with a 5(3)3-s acquisition strategy. A multi-echo gradient echo sequence was used to measure liver T2*. Non-iron-corrected native T1 (ms), calculated as the mean of four slices through the mid-liver, was measured using T1 parametric maps generated off-line. A proprietary T2* correction (Perspectum Diagnostics, Oxford, UK), blinded to native T1 values, calculated cT1 values. The relationship between native T1 and cT1 measurements was assessed using Spearman rank correlation and Bland-Altman analyses.

RESULTS

Forty-eight patients with a mean (standard deviation [SD]) age of 15.2 (4.1) years were included. Mean (SD) liver native T1 was 651.2 (123.9) ms and mean (SD) cT1 was 919.5 (86.8) ms, with excellent positive correlation between values (r=0.91 [95% confidence interval (CI): 0.85-0.95]; P<0.0001). Mean bias between native T1 and cT1 measurements was 268.3 ms (95% limits of agreement: 131.9-404.7 ms).

CONCLUSION

There is excellent positive correlation between liver native T1 and cT1 measurements in pediatric patients with autoimmune liver disease. This relationship brings into question the need to perform T1 iron correction in this patient population. T1 and cT1 measurements are not interchangeable, however, due to considerable systematic bias with cT1 values being considerably higher.

Significance of progressive liver fibrosis in pediatric liver transplants: A review of current evidence

This article reviews the current evidence and knowledge of progressive liver fibrosis after pediatric liver transplantation. This often-silent histologic finding is common in long-term survivors and may lead to allograft dysfunction in advanced stages. Surveillance through protocolized liver allograft biopsy remains the gold standard for diagnosis, and recent evidence suggests that chronic inflammation precedes fibrosis.

Newly Developed Methods for Reducing Motion Artifacts in Pediatric Abdominal MRI: Tips and Pearls

OBJECTIVE. The purpose of this article is to review established and emerging methods for reducing motion artifacts in pediatric abdominal MRI. CONCLUSION. Clearly understanding the strengths and limitations of motion reduction methods can enable practitioners of pediatric abdominal MRI to select and combine the appropriate techniques and potentially reduce the need for sedation and anesthesia.

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.

3D MR elastography of the pancreas in children

PURPOSE

Early diagnosis of chronic pancreatitis (CP) remains elusive. Preliminary data suggest that MR elastography (MRE) may have diagnostic value in the identification of CP. We sought to measure pancreas stiffness by MRE in healthy children and to compare measured values to stiffness values in pediatric patients with acute recurrent pancreatitis (ARP) or CP.

METHODS

Under IRB approval, 49 healthy controls volunteered to be included, and 14 patients with ARP or CP that underwent 3D MRE on a 1.5T MR scanner were included in the study. A soft passive driver was utilized and vibrated at 40 Hz. Regions of interest for measurement of pancreatic stiffness were drawn by two blinded readers and statistical analysis were performed for comparisons between the two groups.

RESULTS

Mean age of the healthy controls was 11 ± 2.7 years and mean pancreas stiffness was 1.7 ± 0.3 (Reader 1) and 1.7 ± 0.3 (Reader 2) kPa. For patients with ARP or CP, mean age was 12.6 ± 4.4 years and mean pancreas stiffness was 0.9 ± 0.2 (Reader 1) and 1.1 ± 0.3 (Reader 2) kPa. Pancreas stiffness was significantly lower in patients with ARP and CP as compared to healthy controls (p < 0.001). Between readers, there was a strong and statistically significant agreement on measured pancreas stiffness (r = 0.81; p < 0.001). Bland-Altman difference analysis showed a mean bias of only 0.05 kPa (95% limits of agreement: - 0.49 to + 0.58) CONCLUSION: MRE of the pancreas can be performed in pediatric patients. Through this study, we have defined normal pancreas stiffness for children and have shown decreases in measured stiffness in patients with ARP or CP compared to healthy controls.

CLINICAL RELEVANCE

3D MRE of the pancreas offers a novel approach for detecting pancreatic disease based on changes in tissue mechanical properties.

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.

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.

Ultrasound Shear Wave Elastography as a Measure of Porcine Hepatic Disease in Right Heart Dysfunction: A Pilot Study

Patients with congenital heart disease with a pressure-overloaded right ventricle can develop liver disease and would benefit from non-invasive diagnostic modalities such as ultrasound shear wave elastography (US SWE). We sought to investigate the ability of US SWE to measure dynamic changes in liver stiffness with an acute fluid bolus in an animal model. Three piglets underwent surgical intervention to create a pressure-overloaded right ventricle and, 12 wk later, underwent US SWE, both pre- and post-intravenous infusion of a saline bolus. Ultrasound measures of shear modulus, velocity and attenuation were taken to characterize hepatic mechanical properties. Liver stiffness exhibited a dynamic component that increased after fluid bolus, although not reaching statistical significance with our small sample size, and these changes were greater in more diseased livers. US SWE may provide a promising non-invasive method for assessing dynamic changes in hydration status and degree of liver disease.

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.

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.

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.