Thyroid scan

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Uptake and Scan


  • Taken up and oranified
  • Oral dose 200-600 uCi (1.5 mCi for thyroid cancer scans)
  • Normal 4 hour uptake is 15%
  • Normal 24 hour uptake is 30%
  • No background uptake differentiates from Tc99m

Tc99m pertechnetate

  • Can also be used but not organified
  • Lower patient dose


Graves Disease - aka diffuse toxic goiter, autoimmune disease caused by autoantibodies to the TSH receptor (aka Thyroid Stimulating Immunoglobulin TSI).

Toxic nodular goiter - Plummer's disease, functionally autonomous nodules, emerges insidiously from multinodular goiter.


  • Chronic (Hasimoto's) - may mimic graves early on and multinodular goiter later, the thyroid gland is gradually destroyed by a variety of cell and antibody mediated immune processes.
  • Acute Bacterial or Subacute Viral - more of a clinical diagnosis, decreased uptake (less than 1% at 24hr), elevated T4 (clinical hyperthyroid).

Cold Nodule - most commonly a colloid cyst, but may represent neoplasm, correlate with US

Hot Nodule - most are benign autonomous adenomas

Multinodular Goiter - enlarged gland with multiple hot and cold nodule giving a patchy appearance. These cold nodules do not have the same risk of cancer as a single cold nodule.

Decreased Uptake

  • Antithyroid drugs (I123 only bc organified)
  • Iodine load (CT contrast)
  • Subacute thyroiditis (viral and painful)
  • Silent thyroiditis (non-tender)

See Also

I 131 therapy