Thyroid
In this newsletter, we focus on thyroid scintigraphy. Thyroid function tests, ultrasound and scintigraphy form the basis for investigation of thyroid disease.
Technetium-99m pertechnetate is administered intravenously and is taken up into the thyroid tissue by the Na/I symporter and allows imaging of thyroid function.
Figure 1: Normal thyroid scan. Note the normal symmetric uptake in both lobes of thyroid (arrow). Mild normal uptake in submandibular salivary glands superiorly.
Indications:
Assessment of thyrotoxicosis Differentiates between Graves’ disease (Fig. 2), thyroiditis and toxic adenomas (Fig.3) Assessment of thyroid nodules Not used for surveillance of thyroid cancer (I-123/I-131 are used)
Figure 2: Graves’ disease: There is intensely increased tracer uptake throughout both lobes of the thyroid gland.
Preparation:
No intravenous X-ray contrast for 6 weeks prior to the test Avoid iodine loading for at least 6 weeks e.g. supplements or medications with a high iodine content Withhold anti- thyroid medications for at least 3 days prior to the test The thyroid scan is usually not performed on hypothyroid patients on thyroid hormone replacement, however if required please contact NMI.
Figure 3: Toxic adenoma: A rounded focus of intense tracer uptake in the mid and lower pole of the left lobe of thyroid with complete suppression of tracer uptake in the remainder of the thyroid.