title: Diagnostic value of CT density in patients with diffusely increased FDG uptake in the thyroid gland on PET/CT images.
abstract: OBJECTIVE
  The purpose of this article is to determine the diagnostic significance of thyroid density as determined by CT in patients with a diffuse hypermetabolic thyroid on PET/CT images.
  
  
  METHODS
  One hundred twelve patients were enrolled in this study, and all underwent PET/CT and a thyroid function test between August 2007 and December 2008. The 56 study patients enrolled had visible (18)F-FDG uptake in the thyroid, whereas the 56 control subjects had no visible FDG uptake. Maximum standardized uptake values (SUV(max)), Hounsfield units, thyroid-stimulating hormone levels, free thyroxine levels, and visual assessments of thyroid CT densities (grades 0-2) were evaluated. Analyses were performed to identify variables that differed between patients and control subjects and to examine relationships between Hounsfield unit and SUV(max) values, free thyroxine level, or thyroid-stimulating hormone level.
  
  
  RESULTS
  Mean Hounsfield unit and SUV(max) values were significantly different between the two groups (p < 0.001), and SUV(max) values were found to be significantly different between grades. Free thyroxine and thyroid-stimulating hormone levels were also significantly different between thyroid density grades 0 and 2 (p < 0.001). A strongly negative relationship was found between Hounsfield units and SUV(max) values (r = 0.75), whereas Hounsfield units were found to be weakly correlated with free thyroxine level (r = 0.36) and thyroid-stimulating hormone level (r = -0.33).
  
  
  CONCLUSIONS
  CT density is closely related to FDG uptake, and low CT density coupled with high FDG uptake suggests a change in thyroid tissue composition and is probably helpful for assessing the disease process and thyroid function of patients whose thyroid show diffuse FDG uptake on FDG PET/CT.
authors.affiliation: Department of Radiology, Hallym University Hangang Sacred Heart Hospital, Yeongdeungpo-gu, Seoul, Republic of Korea. fran9704@hotmail.com <fran9704@hotmail.com>
authors.forename: You Mie
authors.initials: YM
authors.lastname: Han
authors.forename: Young Chul
authors.initials: YC
authors.lastname: Kim
authors.forename: Eun Kyung
authors.initials: EK
authors.lastname: Park
authors.forename: Jae-Gol
authors.initials: JG
authors.lastname: Choe
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18