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Table of Contents
Northern Lincolnshire and Goole NHS Foundation Trust - Nuclear Medicine
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| SOP Code | Title | Review Date |
|---|---|---|
| REF015 | Tc99m Pertechnetate Thyroid Imaging | 2028-01-14 |
| Authorised By | Authorisation Signature (only on master paper copy) | Date Authorised |
|---|---|---|
| Prof G Avery | 2023-08-22 |
REF015 - Tc99m Pertechnetate Thyroid Imaging
Purpose
The purpose of this document is to assist clinicians in deciding on the appropriateness of the Nuclear Medicine procedure and to give guidance on the mechanism of referral.
Background
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.
| ARSAC Licence Holders |
|---|
| Prof Ged Avery |
| Dr Najeeb Ahmed |
| Nuclide | Pharmaceutical Form | Local DRL (MBq) |
|---|---|---|
| Tc99m | Pertechnetate | 80 |
| Typical Radiation Dose (mSv) | 0.5 (for 40MBq) |
|---|
Staff Permitted to Refer
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.
Referring clinicians are reminded of the requirement to avoid unnecessary exposure to ionising radiation. The investigation may already have been requested at this hospital or elsewhere and clinicians are asked to be particularly vigilant to ensure that their request is not a double request.
Acceptance of Referrals
Requests will only be accepted if the diagnostic question fulfills one of the referral criteria below. Appropriate clinical information must be supplied to allow the investigation to be justified.
It is not acceptable to simply request the investigation without appropriate clinical information.
Requests will be returned to the referrer if:
- The diagnostic question is unclear.
- The diagnostic question cannot be answered by the investigation.
- Insufficient clinical information is supplied to justify the investigation.
Requests should be submitted on the orange stripe NUCLEAR MEDICINE (ISOTOPE SCAN) request form. Patient details, Investigation required and Reason for Test/Diagnostic Question should be fully and appropriately completed and the form signed.
Note the requirement for Patient Preparation below
Referral Criteria
Sufficient clinical information must be provided to justify the investigation proceeding.
| Investigation |
|---|
| To assess functionality of thyroid nodules, To assess goitre including hyperthyroid goitre, To assess uptake function prior to radio-iodine treatment, To assess ectopic thyroid tissue, To assess suspected thyroiditis, To assess neonatal hypothyroidism. |
Contraindications
Patient Preparation
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.
References
