thyroid scan (Tc-99m)

Tc-99m pertechnetate thyroid scan is a functional nuclear medicine study used to assess the thyroid gland. The uptake of the pertechnetate anion - similar in chemical-physical characteristics to the iodide ion - in the thyroid parenchyma is mediated by the NIS (Sodium-Iodide Symporter). However, unlike iodine, pertechnetate anion is not incorporated into thyroid hormones.

Technique

• patient preparation
  • fast for 4 hours prior to exam
• radiopharmaceutical
  • Tc-99m pertechnetate
• dose and route of administration
  • 111-185 MBq (3-5 mCi) IV 
• time of imaging
  • 20 minutes after Tc-99m pertechnetate administration
• equipment
  • camera: gamma camera
  • collimator: pinhole
  • window: 20% energy window centered at 140 KeV
• procedure
  • obtain anterior, LAO, and RAO views
  • mark chin, suprasternal notch, palpable nodules, and surgical scars

Interpretation

Radiotracer uptake on the thyroid scan needs to be interpreted with biochemical thyroid function tests and thyroid antibodies (e.g. antithyroglobulin, antimicrosomal, thyrotropin receptor). The combination of these results can usually distinguish between the causes of thyroid dysfunction.

Increased uptake

• Graves disease
• Hashitoxicosis

Normal uptake

• Hashimoto disease
• following I-131 therapy

Decreased uptake

• excess iodine intake
  • amiodarone
  • high iodine diet
  • iodinated contrast
• subacute thyroiditis
• struma ovarii
• Hashimoto disease

Abnormal site of uptake

• ectopic thyroid
• lingual thyroid

See also

• thyroid scan (I-123)

Siehe auch:

• Schilddrüse
• thyroid scan (I-123)
• Tc 99 Pertechnetate

und weiter:

• tc-99m pertechnetate