99mTc-thyroid scan

The 99mTc-Thyroid Scan, also known as thyroid scintigraphy or pertechnetate scan, is a specialized nuclear medicine imaging technique used to assess the structure and function of the thyroid gland. This functional scan is non-invasive and highly effective in diagnosing and differentiating thyroid disorders, particularly in patients presenting with abnormal thyroid hormone levels, thyroid enlargement, or nodules. The scan uses Technetium-99m pertechnetate (99mTc), a radiotracer that is selectively taken up by active thyroid tissue. The uptake and distribution of this tracer in the thyroid help visualize functional abnormalities such as hyperfunctioning ("hot") nodules, non-functioning ("cold") nodules, and diffuse increased uptake, which can point to specific thyroid conditions such as Graves’ disease or toxic nodular goitre. 

This diagnostic test plays a crucial role in the evaluation of hyperthyroidism, thyroid nodules, ectopic thyroid tissue, substernal goitre, and congenital thyroid dysfunction. It is also helpful in distinguishing between different causes of thyroiditis, such as viral or autoimmune thyroid inflammation.

What is a 99mTc-Thyroid Scan?

The 99mTc-Thyroid Scan is a nuclear medicine imaging procedure that evaluates the functional status of the thyroid gland.

It involves the intravenous injection of Technetium-99m pertechnetate, a radioactive tracer taken up by the thyroid in a manner similar to iodine.

The scan provides detailed images that reveal areas of increased, decreased, or absent activity, correlating with thyroid function and pathology.

It is often used alongside thyroid function tests (T3, T4, TSH) and ultrasound imaging for a comprehensive thyroid evaluation.

Indications for a 99mTc-Thyroid Scan

This test is particularly recommended in the following clinical scenarios:

• Differentiation of hyperthyroidism causes, such as distinguishing Graves’ disease from toxic nodular goitre
• Evaluation of thyroid nodules and determining whether they are hot, cold, or warm
• Localization of ectopic thyroid tissue, including lingual or mediastinal thyroid
• Investigation of substernal or neck masses suspected to be thyroid in origin
• Assessment of congenital hypothyroidism, particularly in neonates
• Evaluation of thyroiditis – including viral, autoimmune, or subacute types
• Correlation of palpable thyroid enlargement or masses with functional activity
• Preoperative planning for thyroid surgeries or radioactive iodine therapy
• Post-surgical or post-treatment residual thyroid tissue detection

How is the 99mTc-Thyroid Scan Performed?

Preparation:

• Patients may be asked to avoid iodine-containing medications or contrast agents for several days prior to the test.
• Fasting is usually not required, but you should follow any specific instructions from your healthcare provider.
• Inform the technologist if you are pregnant or breastfeeding.

Procedure Steps:

Radiotracer Injection

• A small amount of Technetium-99m pertechnetate is injected into a vein, typically in the arm.

Uptake Phase

• The patient waits for approximately 15–30 minutes to allow the radiotracer to concentrate in the thyroid gland.

Imaging

• The patient lies still while a gamma camera captures images of the thyroid from multiple angles.
• The scan typically takes 15–20 minutes to complete.

Post-procedure

• Normal activities can be resumed immediately.
• Drinking plenty of fluids is encouraged to help flush the tracer from the body.

Understanding the Scan Results

The thyroid scan images provide vital functional data:

• Diffuse increased uptake – Often associated with Graves’ disease
• Focal increased uptake – Suggests a toxic (hyperfunctioning) nodule
• Cold (non-functioning) nodules – Could be benign or malignant and usually require further investigation (e.g., biopsy)
• Reduced or patchy uptake – May indicate thyroiditis, inflammation, or post-therapy changes
• Absent uptake in expected thyroid area – May suggest ectopic thyroid tissue or thyroid agenesis

Benefits of 99mTc-Thyroid Scan

• Non-invasive and painless imaging procedure
• Provides functional assessment of the thyroid gland, not just structural details
• Helps in early and accurate diagnosis of thyroid disorders
• Assists in distinguishing between different types of hyperthyroidism
• Useful for pre-surgical planning and evaluating the need for radioactive iodine treatment
• Identifies ectopic thyroid tissue or developmental thyroid anomalies
• Aids in the monitoring of previously treated thyroid disease

Is the Test Safe?

The 99mTc-Thyroid Scan is very safe and widely used in clinical practice:

• The amount of radioactive tracer used is minimal and well within safe limits.
• Side effects are rare and usually mild.
• The test is quick, non-invasive, and requires no anesthesia.
• Patients can resume normal activities immediately after the scan.
• As with all nuclear medicine procedures, pregnant or breastfeeding women should consult their physician before undergoing the scan.

Conclusion

The 99mTc-Thyroid Scan, or thyroid scintigraphy, is a highly effective nuclear medicine imaging tool that offers crucial insights into thyroid function and pathology. By utilizing the radiotracer Technetium-99m pertechnetate, this scan highlights the metabolic activity of thyroid tissues, enabling clinicians to detect hyperfunctioning nodules, thyroiditis, Graves’ disease, and ectopic thyroid glands with remarkable accuracy. This functional scan complements structural imaging such as thyroid ultrasound and is essential in evaluating thyroid abnormalities, guiding treatment decisions, and planning surgical or radioactive iodine therapy. As a safe, efficient, and informative test, the 99mTc-Thyroid Scan remains a cornerstone in the diagnosis and management of thyroid diseases.