REF015 - Tc99m Pertechnetate Thyroid Imaging

See REF000 - Referring to Nuclear Medicine (NLAG) for details on how to refer.

The main function of the thyroid gland is to concentrate and organify inorganic iodine, to store the iodinated compounds and then release them as active hormones into the circulation. Although Ultrasound, CT and MRI may define thyroid anatomy, functional characteristics of the gland and of any nodules present are best identified using Nuclear Medicine techniques.

Technetium-99m pertechnetate is concentrated by the thyroid but is not organified into the thyroid hormones. When thyroid imaging is performed with technetium-99m, the scan appearances essentially provide a display of tracer uptake which is dependent on the trapping mechanism of the thyroid gland. In practice, it is possible to obtain the same information as with an iodine radiopharmaceutical, with a few exceptions. The principal exception occurs in some thyroid cancers which trap but do not bind iodine and could appear hot on a pertechnetate scan but cold when using an iodine radiopharmaceutical.

• The referrer may be any UK registered medical practitioner currently employed in Secondary Care.
• Referrals from Primary Care will be accepted if the investigation has been suggested by a a Secondary Care Specialist or a Consultant Radiologist in a report from a previous investigation; or following discussion with a Consultant Radiologist. Details of such suggestions or discussions should be included on the request form.

• Sodium chloride for parenteral use (0.9% w/v).

Follow a low iodine diet for 2 weeks prior to imaging^[2]

• Stop antithyroid medications (e.g. Carbimazole or propylthiouracil(PTU)) for 7 days before the appointment^[2]. These can be restarted following the scan.
• Avoid medications containing iodine for at least 4 weeks prior to imaging (e.g. vitamin and mineral supplements, kelp, Lugol's solution, potassium iodide, and expectorants)^[2]
• Avoid iodinated contrast media (as used in CT and X-ray procedures) for at least 8 weeks prior to imaging^[2]
• Stop thyroxine (T4) 4 weeks prior to imaging. This may be replaced with triiodothyronine (T3) for 2 weeks^[2]
• T3 - whether prescribed to replace the T4 or as a stand alone medication - should be stopped two weeks before the imaging^[2]
• Patients taking Amiodarone may need to withdraw this for 3-6 months prior to imaging. If the patient is taking Amiodarone, discuss the withdrawal of this with the ARSAC Licence holder prior to the patient being appointed for imaging.