Suraj D. Serai

Use of Magnetic Resonance Elastography to Assess Hepatic Fibrosis in Children with Chronic Liver Disease

Management of pediatric chronic liver disease is limited by lack of validated noninvasive biomarkers of histologic severity. We demonstrate that magnetic resonance elastography is feasible and accurate in detecting significant hepatic fibrosis in a case series of 35 children with chronic liver disease, including severely obese children.

Characterization of pediatric liver lesions with gadoxetate disodium.

Gadoxetate disodium (Gd-EOB-DTPA) is a relatively new hepatobiliary MRI contrast agent. It is increasingly used in adults to characterize hepatic masses, but there is little published describing its use in children. The purpose of this paper is to describe our pediatric MRI protocol as well as the imaging appearance of pediatric liver lesions using gadoxetate disodium. As a hepatocyte-specific MRI contrast agent, Gd-EOB-DTPA has the potential to improve characterization and provide a more specific diagnosis of pediatric liver masses.

Pediatric Liver MR Elastography

IntroductionMany 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 MaterialsPediatric MRE techniques were developed and applied to over 45 patients scanned with our new protocol.ConclusionLiver MRE is a safe, non-invasive method for assessing hepatic fibrosis in pediatric patients.

Relationship of MR elastography determined liver stiffness with cardiac function after Fontan palliation

To use MR elastography to assess liver stiffness in patients with congenital heart disease palliated with the Fontan procedure and correlate findings with cardiac index and other functional parameters obtained during cardiac MRI.

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 Imaging of Pediatric Muscular Disorders Recent Advances and Clinical Applications

This review describes various quantitative magnetic resonance imaging techniques that can be used to objectively analyze the composition (T2 relaxation time mapping, Dixon imaging, and diffusion-weighted imaging), architecture (diffusion tensor imaging), mechanical properties (magnetic resonance elastography), and function (magnetic resonance spectroscopy) of normal and pathologic skeletal muscle in the pediatric population.

Linearity, Bias, and Precision of Hepatic Proton Density Fat Fraction Measurements by Using MR Imaging: A Meta-Analysis

Purpose To determine the linearity, bias, and precision of hepatic proton density fat fraction (PDFF) measurements by using magnetic resonance (MR) imaging across different field strengths, imager manufacturers, and reconstruction methods. Materials and Methods This meta-analysis was performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A systematic literature search identified studies that evaluated the linearity and/or bias of hepatic PDFF measurements by using MR imaging (hereafter, MR imaging-PDFF) against PDFF measurements by using colocalized MR spectroscopy (hereafter, MR spectroscopy-PDFF) or the precision of MR imaging-PDFF. The quality of each study was evaluated by using the Quality Assessment of Studies of Diagnostic Accuracy 2 tool. De-identified original data sets from the selected studies were pooled. Linearity was evaluated by using linear regression between MR imaging-PDFF and MR spectroscopy-PDFF measurements. Bias, defined as the mean difference between MR imaging-PDFF and MR spectroscopy-PDFF measurements, was evaluated by using Bland-Altman analysis. Precision, defined as the agreement between repeated MR imaging-PDFF measurements, was evaluated by using a linear mixed-effects model, with field strength, imager manufacturer, reconstruction method, and region of interest as random effects. Results Twenty-three studies (1679 participants) were selected for linearity and bias analyses and 11 studies (425 participants) were selected for precision analyses. MR imaging-PDFF was linear with MR spectroscopy-PDFF (R2 = 0.96). Regression slope (0.97; P < .001) and mean Bland-Altman bias (-0.13%; 95% limits of agreement: -3.95%, 3.40%) indicated minimal underestimation by using MR imaging-PDFF. MR imaging-PDFF was precise at the region-of-interest level, with repeatability and reproducibility coefficients of 2.99% and 4.12%, respectively. Field strength, imager manufacturer, and reconstruction method each had minimal effects on reproducibility. Conclusion MR imaging-PDFF has excellent linearity, bias, and precision across different field strengths, imager manufacturers, and reconstruction methods.

Breathe In... Breathe Out... Stop Breathing: Does Phase of Respiration Affect the Haller Index in Patients With Pectus Excavatum?

OBJECTIVE The purpose of this article is to determine whether the phase of respiration at the time of imaging affects chest wall measurements and compression of internal structures in patients with pectus excavatum. MATERIALS AND METHODS Forty-seven patients (median age, 14 years) imaged for preoperative pectus excavatum underwent limited axial balanced steady-state free precession MRI of the chest at inspiration, expiration, and stop quiet breathing. Two radiologists, who were blinded to prior measurements, independently calculated the Haller index, asymmetry index, and sternal tilt in each phase of respiration. Compression of internal structures was recorded. Statistical comparison was performed. RESULTS The Haller index was significantly lower at inspiration, compared with stop quiet breathing and expiration, with medians (interquartile ranges) of 3.96 (3.27-4.61), 5.16 (4.02-6.48), and 5.09 (4.14-6.63), respectively (p < 0.0001 for both). No significant difference in Haller indexes was observed between expiration and stop quiet breathing (p = 0.1171). Of 11 patients with a Haller index less than 3.25 at inspiration, eight (72.7%) had an index greater than 3.25 on expiration and stop quiet breathing, which accounted for 17% (8/47) of all patients imaged. Compression of the liver or vascular structures was present in 24 (51%) patients. There was no significant difference in the asymmetry index, sternal tilt, or right heart compression between phases of respiration. CONCLUSION Obtaining the Haller Index at inspiration may result in a value significantly lower than that at expiration, potentially affecting surgical and financial decision making. Compression of the liver and vascular structures was observed in 51% of patients, but additional research is needed to determine the clinical significance of this finding.

Limited, fast magnetic resonance imaging as an alternative for preoperative evaluation of pectus excavatum: a feasibility study.

Objective: The purpose of this study was to determine the reliability, feasibility, and image quality of a limited, fast magnetic resonance imaging (MRI) protocol for preoperative evaluation of pectus excavatum in a pediatric population referred for presurgical imaging. Materials and Methods: A total of 47 patients, median age 14 years, referred for preoperative imaging of pectus excavatum, underwent axial balanced steady-state free precession MRI of the chest, with a limited patient charge. Two pediatric radiologists independently conducted a blinded retrospective study. The Haller and asymmetry indices were calculated at the level of greatest anterior-posterior chest narrowing. In addition, right heart compression and image quality were subjectively assessed, and scan duration was determined. Results: Intraclass correlation coefficient reliability was between 0.85 and 0.98, indicating almost perfect agreement for quantitative measurements. Subjective evaluation of right heart compression and image quality showed moderate interreader agreement. Image quality was graded as good or excellent by both readers for all studies. No difference in the Haller index was observed between modalities in 3 patients on both computed tomographic scan and MRI (P=0.2697). The median scan duration was 8 minutes. Conclusions: Limited MRI is a reliable and cost-effective alternative for preoperative assessment of pectus excavatum. It is fast, free of ionizing radiation, and there is excellent interreader reliability for measurements of chest wall deformity.

Quantitative Skeletal Muscle MRI: Part 2, MR Spectroscopy and T2 Relaxation Time Mapping—Comparison Between Boys With Duchenne Muscular Dystrophy and Healthy Boys

OBJECTIVE The purpose of this study is to validate the use of MR spectroscopy (MRS) in measuring muscular fat and to compare it with T2 maps in differentiating boys with Duchenne muscular dystrophy (DMD) from healthy boys. SUBJECTS AND METHODS Forty-two boys with DMD and 31 healthy boys were evaluated with MRI with (1)H-MRS and T2 maps. Grading of muscle fat and edema on conventional images, calculation of fat fractions ([fat / fat] + water) on MRS, and calculation of T2 fat values on T2 maps of the gluteus maximus and vastus lateralis muscles were performed. Group comparisons were made. The 95% reference interval (RI) of fat fraction for the control group was applied and compared with T2 map results. RESULTS Minimal fat on T1-weighted images was seen in 90.3% (gluteus maximus) and 71.0% (vastus lateralis) of healthy boys, versus 33.3% (gluteus maximus) and 52.4% (vastus lateralis) of boys with DMD. Muscle edema was seen in none of the healthy boys versus 52.4% (gluteus maximus) and 57.1% (vastus lateralis) of the boys with DMD. Fat fractions were higher in the DMD group (52.7%, gluteus maximus; 27.3%, vastus lateralis) than in the control group (12.8%, gluteus maximus; 13.7%, vastus lateralis) (p < 0.001). The 95% RI for gluteus maximus (38.7%) resulted in 61.9% sensitivity and 100% specificity for differentiating boys with DMD from healthy boys, whereas the value for vastus lateralis (17.8%) resulted in 76.2% sensitivity and 100% specificity; both had lower accuracy than did T2 maps (100% sensitivity and specificity). There was a positive correlation between T2 fat values and fat fractions (p < 0.0001). CONCLUSION In differentiation of the two groups, T2 maps were more accurate than MRS. Fat fractions can underestimate the actual amount of fat because of coexisting muscle edema in DMD.