title: SPECT/CT characterization of oral activity on radioiodine scintigraphy.
abstract: BACKGROUND
  Oral activity on radioiodine scintigraphy is commonly seen and may cause diagnostic dilemma. Determining the precise mechanism of oral uptake on radioiodine scintigraphy will increase the accuracy and confidence of interpretation and avoid possible misinterpretation.
  
  
  OBJECTIVE
  To determine the etiology of focal persistent radioiodine oral uptake seen on radioiodine scans.
  
  
  METHODS
  Retrospective sequential series at a university clinic and a phantom study experiment.
  
  
  METHODS
  Preablation iodine-131 planar and single photon emission computed tomography/computed tomography (SPECT/CT) scans of 216 patients after total thyroidectomy were reviewed. Planar images were inspected for the presence of oral activity above the salivary gland background and SPECT/CT was reviewed to determine the location and nature of oral activity. A post-hoc phantom study was designed using typodont stone models fitted with various dental materials, immersed in a diluted iodine-131 solution, and imaged with SPECT/CT to characterize radioiodine uptake by high-attenuation dental materials.
  
  
  RESULTS
  Oral activity was seen on planar images in 123 of 216 (57%) patients; 12 patients were excluded from analysis because the SPECT/CT field of view did not cover the entire oral cavity. In the remainding 111 patients SPECT/CT images demonstrated focal uptake localizing to high-attenuation dental material on the CT in 95 of 111 (86%) patients. All cases of oral activity on planar imaging were interpreted as benign etiology on SPECT/CT. The phantom study confirmed focal in vitro uptake within high-attenuation dental materials representing a range of commonly used metal alloys.
  
  
  CONCLUSIONS
  Focal oral activity on diagnostic radioiodine scans frequently localizes to high-attenuation dental material on SPECT/CT. We postulate that an affinity between negatively charged iodide ions (I(-)) in saliva and positively charged metal ions (eg, Ag(+), Hg(+), Au(2+), Pd(2+)) within the dental materials is at the basis of persistent focal radioiodine uptake in the oral cavity. This represents a new mechanism underlying benign radioiodine activity not previously described in the medical literature.
authors.affiliation: University of Michigan, B1G505G University Hospital, 1500 East Medical Center Drive, Ann Arbor, MI 48109-5028. ancaa@med.umich.edu.
authors.forename: Hatice
authors.initials: H
authors.lastname: Savas
authors.forename: Ka Kit
authors.initials: KK
authors.lastname: Wong
authors.forename: Berna
authors.initials: B
authors.lastname: Saglik
authors.forename: David
authors.initials: D
authors.lastname: Hubers
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Ackermann
authors.forename: Anca M
authors.initials: AM
authors.lastname: Avram
mesh_terms: D000284:Administration, Oral; D000328:Adult; D003764:Dental Materials; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D009055:Mouth / Q000000981:diagnostic imaging; D064847:Multimodal Imaging / Q000379:methods / Q000592:standards*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012469:Salivary Glands / Q000000981:diagnostic imaging; D012796:Sialography / Q000379:methods / Q000592:standards*; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods / Q000592:standards*; D014057:Tomography, X-Ray Computed / Q000379:methods / Q000592:standards*
chemical_list: D003764:Dental Materials; D007457:Iodine Radioisotopes