RecruitingDiagnostic testPediatric PET/MR Image RegistryThe purpose of this study is to compare whole body magnetic resonance (MR) imaging, whole body positron emission tomography (PET)/MR imaging, and (if available) PET/Computed Tomography (CT) imaging for the diagnosis of tumors in children and young adults. Sensitivities, specificities and diagnostic accuracies of the different imaging modalities will be compared for significant differences.