Thyroid scintigraphy
The thyroid scintigraphy is a nuclear medicine technique that the functional- examination of the thyroid is applied. It is particularly suitable for differentiating between cold and hot nodes and for assessing the morphology or tissue structure.
principle
The follicle cells of the thyroid gland need iodine for the synthesis of the iodine-containing thyroid hormones. This is used in thyroid scintigraphy. Certain radionuclides are used whose chemical properties are identical to or similar to stable iodine.
The radionuclide is injected into the patient's vein and accumulates in the thyroid gland after about 10 to 20 minutes.
The radiation emitted by the incorporated radionuclides is recorded by a special camera ( gamma camera ) so that the thyroid gland can be displayed and the thyroid function can be assessed. In the case of thyroid autonomy, for example, more radionuclide accumulates in autonomous thyroid cells than in "normal" follicle cells. In addition, the biological half-life of iodine degradation can be measured with several recordings at time intervals and conclusions can be drawn from this for an abnormally increased or decreased activity of the thyroid gland.
Radiopharmaceuticals
In thyroid scintigraphy, radionuclides, so-called radiopharmaceuticals, are used. Sodium - 99m technetium pertechnetate (Na 99m TcO 4 ) is routinely used as a radiopharmaceutical . For special questions, 123 iodine ( 123 I) is also used, and 131 iodine as part of a radioiodine test .
When 99m Tc is a pure gamma emitter with a relatively low effective half-life . In comparison, 131 I is also a beta emitter, and the half-life is longer than that of 99m Tc. 123 I reacts by electron capture (EC) and is a gamma emitter like 99m Tc, but is more expensive and has a half- life that is twice as long as 99m Tc.
Due to the lower radiation exposure for the patient and lower costs, the preferred use of thyroid scintigraphy is 99m Tc. The use of 123 I is reserved for specific questions, for example when it comes to the question of dystopic thyroid tissue or, rarely, the radioiodine test.
Indications
A: normal thyroid B: Graves disease C: autonomous adenoma D: toxic adenoma E: thyroiditis
A thyroid scintigraphy is usually preceded by a palpation of the thyroid, a laboratory medical examination of thyroid parameters and an ultrasound examination (sonography). If, based on these examinations, there is a suspicion of functional changes in the thyroid, in particular functional thyroid autonomy or thyroid cancer , a thyroid scintigraphy may be indicated for further clarification.
With the 99m Tc scintigraphy, statements can be made about the functional significance of morphological changes and a quantitative assessment of the functional changes can be made. In addition, as with ultrasound, statements about the position and size are possible. It is primarily possible to detect cold , warm and hot nodes as well as diffuse additional storage.
interpretation
With the ROI technology, the so-called global and regional 99m Tc uptake , i.e. H. the amount of radionuclide absorbed into the follicular epithelial cells can be determined. Knowledge of the current thyroid parameters ( thyroid hormones ) is required for an adequate interpretation of a thyroid scintigram .
Picture gallery
Thyroid scintigram for a goiter with four autonomous adenomas of different sizes
Scintigraphy of a thyroid with uptake and size in the upper normal range. Above the SD are the submandibular glands to recognize.
Scintigram of the thyroid gland with 131 iodine in preparation for radioiodine therapy .
The image taken with a pinhole collimator is not to scale.
Scintigraphy of an autonomic adenoma
Dystopic goiter on the base of the tongue. Scintigraphy with 123 iodine, view from the side.
literature
- S1 guideline thyroid scintigraphy of the German Society for Nuclear Medicine (DGN). In: AWMF online (as of 2014)
Web links
Information for patients:
Additional information:
- Diagnosis of thyroid diseases . (PDF; 1.5 MB) Springer-Verlag
