MR and Ultrasound for Liver Fat Assessment in Children: Techniques and Supporting Evidence.

Hepatic steatosis is a common imaging finding that can be a sign of chronic liver disease, most often associated with metabolic dysfunction-associated steatotic liver disease (MASLD). Imaging techniques for evaluating steatosis range from basic qualitative assessments to advanced and highly accurate quantitative metrics. Among these, MRI-based proton density fat fraction (PDFF) is widely regarded as a reliable and precise imaging biomarker for quantifying liver steatosis. Additionally, multiple ultrasound platforms now offer quantitative assessments of hepatic steatosis. These methods include attenuation coefficient, speed of sound, backscatter, or other multiparametric approaches such as ultrasound-derived fat fraction (UDFF) which combines attenuation and backscatter quantification. Newer and upcoming quantitative ultrasound methods include acoustic structure quantification (ASQ) and tissue scatter distribution imaging (TSI). Therefore, ultrasound-based liver fat measurements could potentially serve as an effective screening tool in certain clinical settings, such as suspected MASLD. In this review, we describe how, why, and when to use MRI- and ultrasound-based fat quantification techniques for assessing liver steatosis in children. We discuss practical strategies for adapting and optimizing these methods in pediatric settings, considering clinical indications, patient preparation, equipment needs, acquisition techniques, potential pitfalls, and confounding factors. Additionally, guidance is provided for interpretation and reporting, along with illustrative case examples. Evidence Level: N/A Technical Efficacy: Stage 5.