Nuclear Medicine Thyroid Scan

Authors: Cr Chian Chang*
Dr Dee Nandurkar *

What is a thyroid scan?

Thyroid scanning or scintigraphy is a procedure to image the thyroid gland.
99m-Tc pertechenetate is the radiopharmaceutical administered intravenously and imaged on a gamma camera.

What are the generally accepted indications for a thyroid scan?

Common indications for a thyroid scan include:

• to differentiate causes of primary hyperthyroidism;
• to evaluate functionality of a thyroid lesion found on clinical examination;
• to evaluate functionality of a nodule/s found on other imaging tests;
• to evaluate functionality of a nodule/s found on other imaging tests;

For further information and advice please contact your nuclear medicine department.

What are the prerequisites for having a thyroid scan done?

• Previous investigations confirming thyroid pathology by either:
  1. abnormal thyroid function tests (TSH, T4 and T3, thyroglobulin, TSI, TPOAb);
     and/or
  2. ultrasound study of the thyroid gland showing single or multiple nodules.
     (For further information see Diagnositic Imaging Pathways: Endocrine).
• Ensuring that no previous radiological procedure requiring the injection of iodine contrast medium has been carried out 8 weeks before the thyroid scan.
• Ensuring cessation of iodine-containing foods, vitamin supplements and medicines before the scan for a minimum of 1–2 weeks.
• Ensuring cessation of the following drugs before the scan:
  • Thyroxine (at least 1 week);
  • Liothyronine – needs to be ceased for 5 days;
  • Carbimazole;
  • Propylthiouracil;
  • Amiodarone – an antiarrhythmic, contains high-dose iodine. This will affect scan results if used in the 3 months before the scan;
  • Lithium – affects uptake of the radiopharmaceutical. Cessation of lithium will depend on the clinical condition of the patient and risk versus benefit of carrying out the scan.

What are the absolute contraindications for a thyroid scan?

This study may not be suitable for pregnant women. The benefit versus risk should be discussed with the nuclear medicine specialist.

What are the relative contraindications for a thyroid scan?

Radioisotope is secreted in breast milk. Women who are breast-feeding need to make special preparations after the test to stop breastfeeding for 24 hours. Expressing breast milk before the scan is an alternative option. For further information, see InsideRadiology: Nuclear Medicine.

There is no requirement to avoid close contact with small children after a thyroid scan.

What are the adverse effects of a thyroid scan?

There are no known associated risks, but the patient will be receiving a dose of ionising radiation (see InsideRadiology: Radiation risk of medical imaging for adults and children).

Is there any specific post procedural care following a thyroid scan?

There are no post-procedural care requirements.

Are there any alternative imaging tests, interventions or surgical procedures to a thyroid scan?

Ultrasound is routinely used in the characterisation of thyroid nodules and thyroid gland size.

CT or MRI gives additional information regarding retro-sternal extent and anatomical effects on adjacent structures.

*The author has no conflict of interest with this topic.

Page last modified on 14/5/2018.