Thyroid Scan

A thyroid scan is a nuclear medicine imaging test used to evaluate the structure and function of the thyroid gland. It helps diagnose various thyroid disorders, including nodules, goiter, hyperthyroidism, and thyroid cancer.

Types of Thyroid Scans:

1. Radioactive Iodine (I-123 or I-131) Scan

   • Uses radioactive iodine, which is taken up by the thyroid gland.

   • Helps assess thyroid function and detect conditions like Graves’ disease, thyroid nodules, and thyroid cancer.

   • Used in radioactive iodine uptake (RAIU) test to measure how much iodine the thyroid absorbs.

2. Technetium-99m Pertechnetate Scan

   • Uses Tc-99m pertechnetate, which is also absorbed by thyroid tissue but not incorporated into thyroid hormones.

   • Provides quicker imaging compared to iodine scans.

   • Commonly used in hyperthyroidism evaluation.

Indications for a Thyroid Scan:

• Differentiating between hot (overactive) and cold (non-functioning) nodules.

• Diagnosing Graves’ disease (diffusely increased uptake).

• Detecting thyroid cancer metastases (especially post-thyroidectomy).

• Evaluating thyroid inflammation (thyroiditis).

Procedure:

1. A small dose of radioactive iodine (I-123) or technetium-99m is given orally or intravenously.

2. After a waiting period (usually 20 minutes to 6 hours), a gamma camera takes images of the thyroid gland.

3. The results show areas of increased uptake (hyperfunctioning) or decreased uptake (hypofunctioning).

Normal vs. Abnormal Findings:

• Normal: Uniform uptake of tracer throughout the thyroid.

• Hyperfunctioning (“hot” nodules): Areas of increased uptake, often benign (e.g., toxic adenoma).

• Non-functioning (“cold” nodules): Areas with no uptake, potentially malignant (require further biopsy).