PEDIATRIC IMAGING 1517 Liver MR Imaging in Children: Current Concepts and Technique 1 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 characteriza- tion. 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 compo- nent of liver examination to characterize focal lesions and involves capturing snapshots of the passage of contrast material in the arteri- al, portal venous, equilibrium, and sometimes hepatobiliary phases, generally by using T1-weighted three-dimensional gradient-echo se- quences. 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 micro- vasculature 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 hepatobili- ary contrast agent administration are increasingly used to charac- terize 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, de- tection 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 pediat- ric liver MR imaging is important for high diagnostic yield. © RSNA, 2016฀•฀radiographics.rsna.org Govind B. Chavhan, MD Susan Shelmerdine, MD Kartik Jhaveri, MD, FRCPC Paul S. Babyn, MD Abbreviations: FNH = focal nodular hyperpla- sia, FSE = fast spin echo, HCC = hepatocel- lular carcinoma, OATP8 = organic anion trans- porter polypeptide 8, SNR = signal-to-noise ratio, SSFP = steady-state free precession RadioGraphics 2016; 36:1517–1532 Published online 10.1148/rg.2016160017 Content Codes: 1 From the Department of Diagnostic Imaging, The Hospital for Sick Children, 555 University Ave, Toronto, ON, Canada M5G 1X8 (G.B.C., S.S.); Department of Medical Imaging, Uni- versity of Toronto, Toronto, Ontario, Canada (G.B.C., S.S., K.J.); Joint Department of Medical Imaging (University Health Network, Mt Sinai Hospital, and Women’s College Hospital), To- ronto, Ontario, Canada (K.J.); and Department of Medical Imaging, Royal University Hospital, Saskatoon, Saskatchewan, Canada (P.S.B.). Pre- sented as an education exhibit at the 2015 RSNA Annual Meeting. Received February 12, 2016; revision requested March 31 and received April 13; accepted April 20. For this journal-based SA- CME activity, K.J. has provided disclosures (see end of article); all other authors, the editor, and the reviewers have disclosed no relevant relation- ships. Address correspondence to G.B.C. (e-mail: drgovindchavhan@yahoo.com). © RSNA, 2016 After completing this journal-based SA-CME activity, participants will be able to: ■ Discuss key concepts pertinent to liver MR imaging in children. ■ Describe technical aspects of liver MR imaging, including sedation, ra- diofrequency coils, sequences, dynamic imaging, contrast media, and diffusion- weighted imaging. ■ List principles of image interpretation related to focal liver lesions in children. See www.rsna.org/education/search/RG. SA-CME LEARNING OBJECTIVES Introduction Magnetic resonance (MR) imaging is increasingly being used for comprehensive evaluation of liver diseases in children. With the rapid evolution of MR imaging, various technical options are now available to compensate for breathing and other motion during the examina- tion, better assess contrast material passage through the circulation during different phases of enhancement, and better characterize tissues and lesions. Understanding the appropriate technique, pulse sequences, and contrast material to use when performing pediatric liver MR imaging is important for high diagnostic yield. This copy is for personal use only. To order printed copies, contact reprints@rsna.org