**Northern Lincolnshire and Goole NHS Foundation Trust - Nuclear Medicine** 

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[[sqlite:unused:unused:unused:/home/heynmorg/public_html/wikifarm/nlag/data/meta/sops/database.db|
SELECT sop AS "SOP Code",title AS "Title",reviewdate AS "Review Date" FROM sops WHERE sop='REF007'|0]] 
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^  Authorised By  ^  Authorising Role  ^  Authorisation Signature \\  (only on master paper copy)  ^  Date Authorised  |
|  Prof G Avery  |  ARSAC Licence Holder  |    |  2025-01-14  |

====== REF007 - Thyroid Imaging and Uptake Measurement with I-123 ======
See [[referral_criteria:ref000-how_to_refer_to_nlagnm|REF000 - Referring to Nuclear Medicine (NLAG)]] for details on how to refer. 

=====  Description =====
The main functions of the thyroid gland are to concentrate and organify inorganic iodine, to store these iodinated compounds and then to release them as active hormones into the circulation. Functioning thyroid tissue is best identified using nuclear medicine techniques.

In most nuclear medicine studies the radiopharmaceutical Tc<sup>99m</sup> pertechnetate is used. Thyroid tissue concentrates Tc<sup>99m</sup> but does not organify it into thyroid hormones. A thyroid scan with Tc<sup>99m</sup> essentially provides a display of the functioning trapping mechanism of the thyroid gland. A thyroid scan with I<sup>123</sup> is a more prolonged study but further shows the organification of I<sup>123</sup> into thyroid hormones by the functioning thyroid tissue. This type of scan is therefore useful in particular cases. Some thyroid cancers merely trap but do not organify iodine. In this case there would be increased uptake on a Tc<sup>99m</sup> pertechnetate scan but reduced uptake on an I<sup>123</sup> scan.

I<sup>123</sup>is not readily available, it is expensive and it gives a higher radiation dose to the patient than Tc<sup>99m</sup> pertechnetate.  The investigation is more prolonged as the I<sup>123</sup> is organified slowly by the thyroid gland. A typical uptake of 30% I<sup>123</sup> at 24 hours following administration is expected.  

I<sup>123</sup> thyroid imaging is therefore restricted to specific cases where the diagnostic question relates to the presence or absence of organifying thyroid tissue.  

[[sqlite:unused:unused:unused:/home/heynmorg/public_html/wikifarm/nlag/data/meta/arsac/database2019.db|SELECT fullname AS "ARSAC Licence Holders" FROM practitionerlicences  INNER JOIN practitioners,procedurecodes,praclicproc,nuclides,chemicalforms ON practitionerlicences.practitioner=practitioners.id AND praclicproc.plicid=practitionerlicences.id AND praclicproc.procid=procedurecodes.id AND procedurecodes.nuclide_id=nuclides.id AND procedurecodes.chemicalform_id=chemicalforms.id AND practitionerlicences.certificateactive='Y' WHERE procedure_code='123I-93-142'  AND date('now')<=expirydate  ORDER BY expirydate|0]]

[[sqlite:unused:unused:unused:/home/heynmorg/public_html/wikifarm/nlag/data/meta/employers_procedures/drl_database.db|
SELECT nuclide AS Nuclide, pharmaceutical_form AS "Pharmaceutical Form",  
local_drl AS "Local DRL (MBq)" FROM drls INNER JOIN nuclides ON drls.nuclide_id=nuclides.id 
WHERE drls.id=29|0]]


^Typical Radiation Dose (mSv)  | 6.1 (for 20MBq) | 

===== Staff Entitled to Refer =====
  * Any clinician holding a current valid medical qualification currently employed in secondary care.
  * Referrals from primary care will be accepted if the investigation has been suggested by a Consultant Radiologist in a report from a previous investigation or following discussion with a secondary care specialist.  Details of such suggestions or discussions should be included on the request form.

===== Supplementary Drugs =====
  * Sodium chloride for parenteral use (0.9% w/v).

===== Contraindications =====
^Patient Demographics  | Pregnancy [([[https://link.springer.com/article/10.1007/s00259-019-04472-8|EANM practice guideline/SNMMI procedure standard for RAIU and thyroid scintigraphy. European Journal of Nuclear Medicine and Molecular Imaging volume 46, 2514–2525(2019)]])]  \\  Breast Feeding - Express milk in advance. Cease feeding for a minimum of 42 hours post administration. Milk expressed during this period should be dicarded [([[https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1018160/ARSAC_Notes_for_guidance_on_the_clinical_administration_of_radiopharmaceuticals_and_use_of_sealed_radioactive_sources.pdf|ARSAC Notes for Guidance on the Clinical Administration of Radiopharmaceuticals and Use of Sealed Radioactive Sources Sept 2021]])]   |
^Allergies  | NB: Suspected "iodine allergy" is **NOT** a contraindication[([[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3965283/|Puchalski AR & Chopra IJ. Radioiodine treatment of differentiated thyroid cancer despite history of ‘iodine allergy’. Endocrinol Diabetes Metab Case Rep. 2014; 2014: 130084]])] |

===== Patient Preparation =====

  * Follow a low iodine diet for 2 weeks prior to imaging.[(#1)]

== Iodinated Substances ==

  * Patients taking Amiodarone may need to withdraw this for 3-6 months prior to imaging.[(#1)] If the patient is taking Amiodarone, this must be discussed with the referring clinician and/or cardiology and the ARSAC licence holder prior to the patient being appointed for imaging.
  * Avoid iodinated intravenous contrast media (as used in CT and X-ray procedures) for at least 8 weeks prior to imaging.[(#1)]
  * Avoid medications containing iodine (e.g. iodinated contrast agents, antiseptics, eye drops, iodinated multivitamins or mineral supplements, kelp, Lugol's solution, potassium iodide and expectorants) for at least 4 weeks prior to imaging.[(#1)]

== Thyroid Medications ==

  * Stop thyroxine (T4) for four weeks prior to imaging. This may be replaced with triiodothyronine (T3) for two weeks.[(#1)]
  * **Stop tri-iodothyronine (T3) - whether prescribed to replace the T4 or as a stand alone medication - two weeks before the imaging.**[(#1)]
  * Stop anti-thyroid medication (methimazole, carbimazole, propylthiouracil) for a minimum of 7 days before the test[(#1)][([[http://snmmi.files.cms-plus.com/docs/Thyroid_Scintigraphy_1382732120053_10.pdf|ACR–SNM–SPR Practice Guideline for the Performance of
Thyroid Scintigraphy and Uptake Measurements]])] . These may be restarted following the scan.
  
  *  Ask the patient to remove chains and/or necklaces from their neck prior to imaging.




===== Clinical Indications =====
^  Investigation  ^
|Localisation and assessment of residual thyroid tissue following resection or partial resection  |
|Localisation and assessment of residual thyroid tissue following radioiodine treatment  |
|Localisation and assessment of ectopic thyroid tissue including struma ovarii  |
|Localisation and assessment of retro-sternal thyroid tissue  |
|To assess neonatal hypothyroidism  |





~~DISCUSSION~~