title: Effect of recent contrast-enhanced CT and patient age on image quality of thyroid scintigraphy.
abstract: OBJECTIVE
  When thyroid scintigraphy (TS) is performed after contrast-enhanced CT (CE-CT), tracer uptake of 99mTcO4 in the thyroid gland can be inhibited by free iodide. Currently, it is recommended to postpone TS until 4 to 8 weeks after CE-CT, but few data exist to support this recommendation. The purpose was to investigate the effect of CE-CT and other variables for the diagnostic quality of TS.
  
  
  METHODS
  This retrospective study included 196 patients subjected to TS less than 3 months after a CE-CT (median, 66 days). Patients with elevated thyroid-stimulating hormone (>4.5 mIU/L) or suspected thyroiditis were excluded. Logistic regression was used to calculate the probability of a TS of diagnostic quality with the variables days since CE-CT, age, thyroid-stimulating hormone, and kidney function (eGFR).
  
  
  RESULTS
  Days since CT and age were highly significant (P < 0.001) predictors for diagnostic TS. The probability of diagnostic quality TS after CE-CT increased with time and reached approximately 70% to 80% 6 to 8 weeks after CE-CT. Analysis of age-specific populations showed age to be a strong independent factor.
  
  
  CONCLUSIONS
  Our findings are in consensus with the currently recommended interval of 6 to 8 weeks between CE-CT and TS. However, our results indicate that patient age should be taken into account, and we suggest the following delay from CE-CT to TS: 4 weeks for patients aged younger than 50 years, 6 weeks for patients aged 50 to 60 years, and 8 weeks for patients aged older than 60 years.
authors: From the *Department of Nuclear Medicine, Aalborg University Hospital, Aalborg; †Department of Nuclear Medicine, Aarhus University Hospital, Aarhus N; and ‡Department of Clinical Medicine, University of Aalborg, Aalborg, Denmark.
authors: Trine Borup
authors: TB
authors: Andersen
authors: Ramune
authors: R
authors: Aleksyniene
authors: Lars Christian
authors: LC
authors: Gormsen
authors: Lars
authors: L
authors: Jødal
authors: Lars J
authors: LJ
authors: Petersen
mesh_terms: D000367:Age Factors; D000368:Aged; D016022:Case-Control Studies; D003287:Contrast Media; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D013670:Sodium Pertechnetate Tc 99m; D013961:Thyroid Gland / Q000000981:diagnostic imaging* / Q000254:growth & development; D013966:Thyroiditis / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D019275:Radiopharmaceuticals; D013670:Sodium Pertechnetate Tc 99m