Keywords: 18F-FDG PET/CT, 18F-fluorodeoxyglucose positron emission tomography/computed tomography; CMR, cardiac magnetic resonance; ECD, Erdheim-Chester disease; Erdheim-Chester disease; LCH, Langerhans cell histiocytosis; RA, right atrial; RDD, Rosai-Dorfman disease; cardio-oncology; pericardial disease.