Signal intensity patterns in health and disease: basics of abdominal magnetic resonance imaging in children

Magnetic resonance imaging (MRI) is playing an increasing role in pediatric abdominal imaging, especially in the evaluation of diffuse parenchymal disease where other imaging modalities might be less sensitive. While quantitative imaging is slowly being incorporated into clinical imaging, qualitative assessment of visceral signal intensity should be part of the routine clinical workflow of all radiologists. Based on their T1 and T2 weighting, the liver, spleen, kidneys and pancreas have characteristic signal intensity patterns with respect to one another and to skeletal muscle. It is important to recognize normal signal intensity patterns of viscera and their evolution with patient age to be able to identify age-related variations and accurately identify diffuse parenchymal disease. Knowledge of normal signal intensity patterns can also help identify ectopic locations of normal tissue such as splenic rests and splenosis. In this review, we discuss normal signal intensity patterns of upper abdominal viscera and their variations on commonly used sequences in pediatric abdominal MRI. We also review normal variations in the perinatal period. Knowledge of these patterns can help pediatric radiologists become more astute in their interpretation of diffuse parenchymal disease in the abdomen.