MRI and ultrasound for hepatic fat quantification:relationships to clinical and metabolic characteristics of pediatric nonalcoholic fatty liver disease

Abstract

The aims of this study were to evaluate hepatic steatosis severity in a series of obese children through both magnetic resonance imaging (MRI) and ultrasound, and to correlate imaging findings to clinical and metabolic characteristics of the study population. Fifty obese children presenting hepatomegaly and/or elevated aminotransferases were candidates for assessment of hepatic fat fraction (HFF) by MRI. All subjects underwent dual energy X-ray absorptiometry scan measurement, and liver ultrasound scanning. Fasting blood samples were taken for the estimation of serum concentrations of glucose, insulin, leptin, aminotransferases and serum lipid profile. A diagnosis of fatty liver was established by MRI in 20 (40%) children; of these, 12 had HFF of 9-18%, while the remaining ones had HFF of 19% or higher. HFF was not correlated to age, SDS-BMI, pubertal status and fat mass. HFF was positively associated with serum concentrations of alanine aminotransferase (ALT; r=0.62; p<0.0001) and AST (r=0.39; p=0.006), as well as with insulin (r=0.44; p=0.001) and insulin resistance (r=0.49; p<0.0001). Overall, ultrasound correlated well with MRI (p<0.0001). However, HFF ranged greatly in subjects with moderate (2-37%) as well as with severe (11-25%) degree of ultrasound hepatic steatosis. In fact, the mean hepatic fat fraction in children with severe steatosis was not statistically different from that found in patients with moderate steatosis (p=0.98). In multiple regression analysis, the most powerful predictors of elevated ALT, after correction for age, gender, BMI and pubertal status, were insulin resistance (p<0.01) and MRI HFF (p<0.0001). Unlike sonography, an operator-dependent procedure, MRI is not subject to interpretation or inter-observer variation, and may be more useful than ultrasound for the monitoring of young patients with hepatic steatosis.