title: Defining optimal tracer activities in pediatric oncologic whole-body18F-FDG-PET/MRI.
abstract: OBJECTIVE
  To explore the feasibility of reducing administered tracer activities and to assess optimal activities for combined18F-FDG-PET/MRI in pediatric oncology.
  
  
  METHODS
  3018F-FDG-PET/MRI examinations were performed on 24 patients with known or suspected solid tumors (10 girls, 14 boys, age 12 ± 5.6 [1-18] years; PET scan duration: 4 min per bed position). Low-activity PET images were retrospectively simulated from the originally acquired data sets using randomized undersampling of list mode data. PET data of different simulated administered activities (0.25-2.5 MBq/kg body weight) were reconstructed with or without point spread function (PSF) modeling. Mean and maximum standardized uptake values (SUVmeanand SUVmax) as well as SUV variation (SUVvar) were measured in physiologic organs and focal FDG-avid lesions. Detectability of organ structures and of focal18F-FDG-avid lesions as well as the occurrence of false-positive PET lesions were assessed at different simulated tracer activities.
  
  
  RESULTS
  Subjective image quality steadily declined with decreasing tracer activities. Compared to the originally acquired data sets, mean relative deviations of SUVmeanand SUVmaxwere below 5 % at18F-FDG activities of 1.5 MBq/kg or higher. Over 95 % of anatomic structures and all pathologic focal lesions were detectable at 1.5 MBq/kg18F-FDG. Detectability of anatomic structures and focal lesions was significantly improved using PSF. No false-positive focal lesions were observed at tracer activities of 1 MBq/kg18F-FDG or higher. Administration of18F-FDG activities of 1.5 MBq/kg is, thus, feasible without obvious diagnostic shortcomings, which is equivalent to a dose reduction of more than 50 % compared to current recommendations.
  
  
  CONCLUSIONS
  Significant reduction in administered18F-FDG tracer activities is feasible in pediatric oncologic PET/MRI. Appropriate activities of18F-FDG or other tracers for specific clinical questions have to be further established in selected patient populations.
authors: Department of Radiology, Diagnostic and Interventional Radiology, University of Tübingen, Tübingen, Germany. sergios.gatidis@med.uni-tuebingen.de.|, Hoppe-Seyler-Str. 3, 72076, Tübingen, Germany. sergios.gatidis@med.uni-tuebingen.de.
authors: Sergios
authors: http://orcid.org/0000-0002-6928-4967
authors: S
authors: Gatidis
authors: Department of Radiology, Diagnostic and Interventional Radiology, University of Tübingen, Tübingen, Germany.
authors: Holger
authors: H
authors: Schmidt
authors: Department of Radiology, Nuclear Medicine, University of Tübingen, Tübingen, Germany.
authors: Christian
authors: C
authors: la Fougère
authors: Department of Radiology, Diagnostic and Interventional Radiology, University of Tübingen, Tübingen, Germany.
authors: Konstantin
authors: K
authors: Nikolaou
authors: Department of Radiology, Diagnostic and Interventional Radiology, University of Tübingen, Tübingen, Germany.
authors: Nina F
authors: NF
authors: Schwenzer
authors: Department of Radiology, Diagnostic and Interventional Radiology, University of Tübingen, Tübingen, Germany.
authors: Jürgen F
authors: JF
authors: Schäfer
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D004305:Dose-Response Relationship, Drug; D005240:Feasibility Studies; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000008:administration & dosage*; D006801:Humans; D007223:Infant; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D064847:Multimodal Imaging / Q000379:methods; D009369:Neoplasms / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography / Q000379:methods*; D011829:Radiation Dosage; D000069079:Radiation Exposure / Q000032:analysis / Q000517:prevention & control*; D011835:Radiation Protection / Q000379:methods*; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D051598:Whole Body Imaging / Q000379:methods; D014915:Whole-Body Counting / Q000379:methods
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: Children; FDG; PET/MRI; Radiation dose; Tracer dose