Rotraud K Saurenmann1, Christian J Kellenberger2. 1. Division of Rheumatology, Zurich University Children's Hospital; and Department of Pediatrics, Cantonal Hospital Winterthur, Winterthur; traudel.saurenmann@kispi.uzh.ch. 2. Diagnostic Imaging, Zurich University Children's Hospital, Zurich, Switzerland.