Liver MR Imaging in Children: Current Concepts and Technique.

Magnetic resonance (MR) imaging is increasingly being used for comprehensive evaluation of liver diseases in children because of the lack of radiation and better lesion detection and characterization. Liver examination involves routine sequences such as T2-weighted, balanced steady-state free precession, and in-phase and out-of-phase sequences. Dynamic imaging is an essential component of liver examination to characterize focal lesions and involves capturing snapshots of the passage of contrast material in the arterial, portal venous, equilibrium, and sometimes hepatobiliary phases, generally by using T1-weighted three-dimensional gradient-echo sequences. Optimal arterial phase imaging is important for detection and characterization of hypervascular lesions. In the equilibrium phase, the concentration of contrast material is similar in the microvasculature and the extracellular interstitial space. Some superficial, spreading, inflammatory lesions are better seen on equilibrium phase images. Meticulous attention to intravenous access and use of an appropriate timing method are critical for successful dynamic imaging. Commonly used contrast media for liver imaging include gadolinium-based extracellular contrast agents and hepatobiliary contrast agents. A portion of hepatobiliary contrast agents such as gadoxetate and gadobenate is taken up by hepatocytes and excreted through bile. Hepatobiliary phase images acquired after hepatobiliary contrast agent administration are increasingly used to characterize liver lesions in children, such as focal nodular hyperplasia. Interpretation of liver MR images involves synthesis of information acquired from evaluation of background hepatic parenchyma, detection of lesions, and evaluation of signal intensity characteristics on images obtained with various sequences to arrive at a diagnosis or reasonable differential diagnoses. Understanding the appropriate technique, sequences, and contrast media when performing pediatric liver MR imaging is important for high diagnostic yield. (©)RSNA, 2016.