PET-MRI in Diagnosing Patients With Cancer, Cardiac Diseases, or Neurologic Diseases

Inclusion Criteria: * Clinically indicated PET/PET-CT (with or without clinically indicated diagnostic MRI) * Presenting with one of the four conditions specified below * Fludeoxyglucose F 18 (FDG) avid cancers * Cardiac disease (cardiac viability assessment) * Neurologic disorders (dementia) * Inflammatory disease (for example fever of unknown origin, vasculitis, osteomyelitis) Exclusion Criteria: * Pregnancy and lactation * Contraindications to undergo MRI * Cardiac pacemaker and metal devices (as specified in a separate MRI Informed consent) * Claustrophobia or inability to tolerate MRI examination (lay still for approximately 1 hour and hold breath intermittently) * Previously known allergies against MRI contrast agents (exclusion criterion only for contrast enhanced MRI) * Renal insufficiency: glomerular filtration rate (GFR) \< 40ml/min/1.73m\^2 and following European Society of Urogenital Radiology (ESUR) guidelines (exclusion criterion only for contrast enhanced MRI) * Individuals who are not willing or capable of giving informed consent or assent (with legal guardian consent)