Gravar-mail: Functional Imaging of SDHx-Related Head and Neck Paragangliomas: Comparison of (18)F-Fluorodihydroxyphenylalanine, (18)F-Fluorodopamine, (18)F-Fluoro-2-Deoxy-d-Glucose PET, (123)I-Metaiodobenzylguanidine Scintigraphy, and (111)In-Pentetreotide Scintigraphy