False-Positive Radioiodine Scintigrams of Differentiated Thyroid Cancer

A description of the physiology and biodistribution of radioiodine along with examples of radioiodine scintigrams to aid in proper differentiation of a false positive finding from a true metastasis in patients with differentiated thyroid cancer.

Course ID: Q00525 Category:
Modalities: , ,


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Targeted CE per ARRT’s Discipline, Category, and Subcategory classification for enrollments starting after January 30, 2024:

Nuclear Medicine Technology: 2.50
Procedures: 2.50
Endocrine and Oncology Procedures: 2.50


  1. Introduction
  2. Radioiodine Physiology and Biodistribution
  3. Radioiodine Imaging Protocol
  4. Functional Radioiodine Uptake Caused by Sodium-Iodide Symporter Expression
  5. Radioiodine Retention
  6. Radioiodine Uptake in Nonthyroid Neoplasms
  7. Radioiodine Uptake from Inflammatory or Infectious Causes
  8. Radioiodine Contamination
  9. Unknown Causes with Clinical Follow-up and Hypothesis
  10. Conclusion


Upon completion of this course, students will:

  1. describe radioiodine concentration in remnant thyroid tissue and differentiated thyroid cancer cells
  2. list what must be known before entertaining 131I therapy
  3. understand thyroid cancer histopathologic results
  4. describe how SPECT/CT can reduce the incidence of false positive findings
  5. identify the mechanisms of radioiodine uptake that lead to false positive findings
  6. explain why thyroid hormone is important
  7. understand the various routes of ingested radioiodine excretion
  8. describe the biochemical processes of iodine uptake
  9. explain how coupling of iodotyrosines produces T3 and T4
  10. describe the physical properties of 131I
  11. describe the physical properties of 123I
  12. explain the different methods of TSH elevation
  13. identify required information for 131I dose selection
  14. be familiar with the process of thyroid embryogenesis
  15. know the various nonthyroid structures that use the sodium-iodide symporter for concentrating radioiodine
  16. recognize what technical imaging considerations could be employed to reduce false positive interpretation in a lactating patient
  17. describe how salivary glands concentrate radioiodine
  18. explain the image pattern associated with thymus gland uptake of radioiodine and what patient population this affects
  19. describe additional imaging techniques that can reduce the false positive interpretation of thymic radioiodine uptake
  20. describe an imaging artifact associated with swallowed saliva and refluxed gastric secretions
  21. list the various gastrointestinal anomalies that can cause false positive findings
  22. understand the physiologic excretion of radioiodine from the colon
  23. know what can lead to blood pool stasis and how it can create false positive uptake on radioiodine scintigraphy
  24. describe how false positive findings can result from urinary retention within the renal collecting system
  25. describe how distal bowel activity could be identified as metastatic disease
  26. explain how dental restoration materials can be problematic on radioiodine imaging
  27. describe the proposed mechanisms of radioiodine uptake associated with nonthyroid neoplasms
  28. describe how a Warthin tumor concentrates radioiodine
  29. know the mechanisms associated with radioiodine uptake in inflammatory conditions
  30. know how to differentiate pulmonary metastases from pulmonary inflammation
  31. understand how perspiration can lead to false positive findings
  32. describe what can be done when contamination on radioiodine imaging is suspected
  33. recognize how bilateral lower extremity radioiodine uptake could be mistaken for metastatic disease
  34. know how to reduce false positive findings when radioiodine uptake is visualized in areas not associated with any proposed mechanism of uptake
  35. understand the variety of confounding false positive findings and what can be done to reduce image misinterpretation