Thyroid scintigraphy is a diagnostic nuclear medicine procedure that can be used for both functional and morphologic examination of the thyroid gland. The examination procedure is of particular importance in assessing the activity of nodules of the thyroid gland.
Indications (areas of application)
- Palpable or sonographically detectable nodular changes of the thyroid gland or suspicion of thyroid malignancy in the presence of a definable focal finding – in this case, thyroid scintigraphy is typically used for further diagnostic clarification. This provides information on the global and regional functional status of the thyroid gland and allows identification of hyperfunctional (hot) and hypofunctional (cold) nodules. Scintigraphically suspect (suspicious) nodes (e.g., cold nodes) are subsequently subjected to fine-needle biopsy and examined histologically (fine-tissue).
- Suspected thyroid autonomy in the presence of hyperthyroidism (hyperthyroidism) – in hyperthyroidism, there may be functional diffuse (distributed) or focal (originating from one focus) autonomy of the thyroid gland, which can be clarified by scintigraphy. Thyroid autonomy is understood as an autonomy of parts of the thyroid tissue from the thyrotropic control circuit (hypothalamus-pituitary-thyroid). This leads to a non-demand production of thyroid hormones.
- Diagnosis confirmation in unclear chronic lymphocytic thyroiditis (Hashimoto’s thyroiditis (thyroiditis); this is characterized by a diffuse or focal lymphocytic infiltration of the thyroid gland – in diagnostically unclear cases in the delineation of Graves’ disease against chronic lymphocytic thyroiditis thyroid scintigraphy is a diagnostically relevant procedure.
- Postoperative diagnostics – thyroid scintigraphy represents a method of choice when assessing the success of therapy after thyroidectomy (removal of the thyroid gland) or radioiodine therapy.
- Progressive diagnostics – thyroid scintigraphy is also important in untreated focal autonomy of the thyroid gland.
Contraindications
Relative contraindications
- Lactation phase (breastfeeding phase) – breastfeeding must be interrupted for 48 hours to prevent risk to the child.
- Repeat examination – no repeat scintigraphy should be performed within three months due to radiation exposure.
Absolute contraindications
- Gravidity (pregnancy)
Before the examination
- Preliminary examinations – before thyroid scintigraphy is performed, a palpatory examination (palpation) of the thyroid gland and thyroid sonography are usually performed.
- Discontinuation of thyroid medications – for a meaningful thyroid examination, discontinuation of thyroid hormone medication or thyrostatic medication is necessary, as the intake of these medications may affect the uptake of the radiopharmaceutical. The exception, of course, is suppression scintigraphy, where taking thyroid hormone medication is a prerequisite. Before thyroid scintigraphy is performed, triiodothyronine (T3) preparations must be discontinued ten days before the examination is performed. Levothyroxine (T4) preparations must be discontinued even four weeks before the examination. Furthermore, it should be noted that after exposure to iodine (eg contrast agent) or blockade of iodine uptake by perchlorate thyroid scintigraphy is not possible (due toiodine blockade of the thyroid gland; the radiopharmaceutical can thus no longer be absorbed!).
- Application of the radiopharmaceutical – the most commonly used radiopharmaceutical for performing thyroid scintigraphy is 99mTechnetium pertechnetate, which is applied intravenously before scintigraphy.
The procedure
The basic principle of thyroid scintigraphy is based on the detection of γ-radiation released by the radiopharmaceutical using a γ-camera. The previously intravenously applied radiopharmaceutical 99mTechnetium-pertechnetate is taken up by the thyroid gland via a sodium–iodide symporter (special transport mechanism) after a distribution phase lasting a few minutes. After transport, the decay rate can thus be calculated.This requires the creation of a scintigram using the γ-camera. To assess functional changes in the thyroid gland, a so-called “region of interest” is defined and the radioactive decay in this area is plotted against time. The decay rate determined in this way is then compared with the decay rate of the radiopharmaceutical before intravenous injection. With the help of this procedure, functional changes can be sensitively detected. This provides information on the global and regional functional status of the thyroid gland and allows identification of hyperfunctional (hot) and hypofunctional (cold) nodes or districts. The scintigram must be obtained within 20 minutes of injection to avoid reducing the validity of the procedure. The measurement itself takes approximately five minutes.
After the examination
The measures to be taken after scintigraphy has been performed depend on the results of the examination. If the findings are negative, no post-examination measures are usually required. Because of the rapid elimination of 99mTechnetium pertechnetate, no special measures are required afterward. In thyroid scintigraphy, radiation exposure from the applied radiopharmaceutical does not pose a risk of complications.
Possible complications
- Intravenous application of radiopharmaceutical may result in local vascular and nerve lesions (injuries).
- Radiation exposure from the radionuclide used is rather low. Nevertheless, the theoretical risk of radiation-induced late malignancy (leukemia or carcinoma) is increased, so that a risk-benefit assessment should be performed.
- Suppression scintigraphy – thyroid scintigraphy is generally free of complications. However, in the course of suppression scintigraphy, the administration of thyroid hormone medication may cause circulatory-associated complications, but these are very rare.
