title: Incidence and intensity of F-18 FDG uptake after vaccination with H1N1 vaccine.
abstract: OBJECTIVE
  To analyze the effect of H1N1 influenza A virus vaccination in patients referred for staging or follow-up F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) for different malignant tumors.
  
  
  METHODS
  Medical history of all patients scheduled for FDG PET/CT during the national vaccination campaign against H1N1 was evaluated for recent vaccination. Site of injection and time between PET/CT and the date of vaccination (dTime) was determined. A difference in the maximum SUV between ipsi- and contralateral deltoid muscle or axillary lymph node of more than 0.5 was determined as positive reaction. The best cut-off dTime for still visible reaction was calculated. All patients with positive ipsilateral lymph node were clinically followed. Institutional Review Board approval was waived.
  
  
  RESULTS
  Of 269 patients, 58 (21.5%) were vaccinated for the H1N1 within 4 weeks prior to PET/CT (mean, 14.5 ± 8.7 days). Of them, 17 (29.3%) patients had FDG-positive lymph nodes (mean SUV, 1.43 ± 1.06), with a dTime range from 1 to 14 days. Only 2 of them had no increased FDG uptake in the ipsilateral deltoid muscle. The area under the receiver operator characteristic curve revealed a strong relation between time delay (dTime) and axillary activity (AUC, 0.9; 95% confidence interval, 0.816-0.983) with a cutoff at 8 days (Youden Index). At follow-up (mean, 183 days; range, 173-196 days), no patient was found to have required treatment or signs of axillary lymphadenopathy.
  
  
  CONCLUSIONS
  H1N1 vaccination can cause false-positive FDG PET/CT findings, when administered less than 14 days before the test, with the highest probability if the vaccination was administered less than 8 days ago. Increased FDG activity in the ipsilateral deltoid muscle is a key finding for accurate interpretation of increased FDG activity in axillary lymph nodes.
authors: Division of Nuclear Medicine, Department Medical Radiology, University Hospital of Zurich, Zurich, Switzerland. Irene.burger@usz.ch
authors: Irene A
authors: IA
authors: Burger
authors: Lars
authors: L
authors: Husmann
authors: Thomas F
authors: TF
authors: Hany
authors: Daniel T
authors: DT
authors: Schmid
authors: Niklaus G
authors: NG
authors: Schaefer
mesh_terms: D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D008198:Lymph Nodes / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D012372:ROC Curve; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D014611:Vaccination
chemical_list: D019788:Fluorodeoxyglucose F18