An imaging test called thyroid scintigraphy, also known as an isotopic thyroid examination, measures how well the thyroid tissue has been able to absorb a radioactive substance that has previously been injected into the body (orally or intravenously). A unique gamma camera is used for the examination. This allows for the examination of thyroid tumors and goiters as well as the morphology of the gland and the detection of thyroid tissue outside of the organ.
The radiotracer most frequently used in thyroid scintigraphy is technetium-99m (99m Tc). Iodine-131 (131I) is used less frequently. The patient must take the I-131 capsule orally 24 hours prior to the exam, while the first is given orally or intravenously 1 hour or 15 minutes prior to the examination, respectively.
Together with thyroid scintigraphy, the assessment of iodine uptake of this gland, i.e. the degree of iodine uptake after administration of radioactive iodine to the body, is often performed .
Thyroid scintigraphy – indications for examination
Thyroid scintigraphy is performed to:
- assessment of the size and location of the thyroid gland,
- thyroid goiter assessment,
- assessment of thyroid tumor function,
- differential diagnosis of hyperthyroidism,
- diagnosis of congenital defects and thyroid disorders,
- establishing the presence of retrosternal or ectopic goiter,
- qualification for radioiodine therapy,
- in suspected thyroid cancer.
Thyroid scintigraphy: how to prepare?
There are some prerequisites for thyroid scintigraphy. The main concern is the potential impact of various variables on the thyroid gland’s ability to absorb radioiodine.
As part of preparation for thyroid scintigraphy, the patient:
- cannot take for at least 3 weeks before the thyroxine test,
- at least 5 days earlier should discontinue antithyroid drugs,
- up to 8 weeks before the examination, should not undergo a test with intravenous contrast agent with iodine,
- before the examination, he should avoid food with a high content of iodine (e.g. sea fish, algae, supplements or medicines),
- you should tell your doctor if you think you may be pregnant and if you are breast-feeding.
The process appears slightly different depending on which isotope is used. The patient must take the capsule containing radioisotope 131I 24 hours prior to the test if it is used. You will receive technetium right before the test if it’s necessary, which is more often the case. The primary imaging process lasts a short time. During this time, the patient remains motionless. You don’t need to be completely empty before the exam.
Thyroid scintigraphy: interpretation of results
The specialist can determine the cause of thyroid disorders (such as a picture typical of Graves’ disease or Hashimoto’s disease) and assess the changes based on the image of the radioisotope distribution.
It is possible to gauge the level of iodine accumulation during thyroid scintigraphy. Based on this, “hot” and “cold” focal lesions (thyroid nodules) can be distinguished. The radioisotope is more strongly captured by “hot” nodules than by other tissues. These changes are typically benign. These primarily consist of adenomas. It is crucial to note that the identified “hot” nodules turn out to be cancerous lesions in about 5% of cases.
“Cold” nodules capture the isotope poorly and may be:
- malignant tumors,
- inflammatory foci,
- lymph node.
In the case of the diagnosis of “cold” nodules during scintigraphy, it is recommended to perform additional diagnostics in the form of thyroid ultrasound as well as a thyroid biopsy .
Recommendations after the examination
You can resume your regular activities right away after the thyroid scintigraphic examination. However, it is advised to drink a lot of water (roughly 1.5 liters) right away following the test to flush out the radioisotope’s remnants.
Thyroid scintigraphy: contraindications
Thyroid scintigraphy is a safe examination, but it should not be used in pregnant and lactating women . During the scintigraphic examination, the patient is exposed to small amounts of radiation.