From the Guidelines
A thyroid radioactive uptake and scan should be performed using Iodine-123 (I-123) due to its superior imaging quality, as stated in the study by 1. The protocol for this procedure involves the patient ingesting a small dose of radioactive iodine, typically 200-400 μCi for I-123, in capsule or liquid form. Patients must fast for 2-4 hours before and after ingestion and discontinue medications that affect thyroid function, including levothyroxine and antithyroid medications like methimazole, as well as avoid iodine-containing foods, supplements, and contrast media for 2-4 weeks. The uptake portion measures the percentage of radioactive iodine absorbed by the thyroid at specific intervals, usually 4-6 hours and 24 hours after ingestion, using a gamma probe placed over the neck. The scan portion involves imaging the thyroid with a gamma camera to visualize the distribution of the radiotracer, typically performed 24 hours after ingestion. According to the study by 1, this procedure is usually appropriate for the initial imaging of thyrotoxicosis, and the nuclear medicine studies are equivalent alternatives and complementary with US. Some key points to consider when performing a thyroid radioactive uptake and scan include:
- The use of I-123 is preferred over I-131 due to its superior imaging quality 1
- The procedure is painless and exposes patients to minimal radiation
- Results help diagnose conditions like hyperthyroidism, hypothyroidism, thyroiditis, and nodules by showing how actively the thyroid absorbs iodine and revealing structural abnormalities
- The procedure should be performed in conjunction with other imaging modalities, such as US, to provide a comprehensive evaluation of the thyroid gland 1.
From the Research
Protocol for Thyroid Radioactive Uptake and Scan
The protocol for a thyroid radioactive uptake and scan involves several steps and considerations, including:
- The use of radioiodine uptake (RAIU) testing with 123I or 131I to evaluate and quantify iodine uptake and kinetics within thyroid cells 2
- Scintigraphic evaluation with 123I or 99mTc-pertechnetate (99mTc04-) to provide the topographic distribution of thyroid cell activity and detect ectopic thyroid tissue 2
- The choice of radionuclide for the tests, with 123I and 131I being commonly used 3
- Factors that can alter uptake results, such as exogenous iodine overload, and the need to exclude these factors before testing 2, 3
- The use of thyroid scintiscanning to identify normal and ectopic thyroid tissue, diagnose the cause of hyperthyroidism, and evaluate thyroid nodules 3
- The measurement of thyroid uptake using a gamma camera-based method, which can be accurate and reproducible 4
- The use of a collar detection device, such as the Collar Therapy Indicator (COTI), to provide real-time quantitation of thyroidal radioiodine uptake in thyroid disease 5
Clinical Applications
The thyroid radioactive uptake and scan has several clinical applications, including:
- Differentiating between destructive and productive thyrotoxicosis 2
- Diagnosing the cause of hyperthyroidism and selecting the appropriate treatment 2, 3
- Evaluating thyroid nodules and informing clinical decision making 2, 3
- Calculating the administered therapeutic activity of 131I to treat hyperthyroidism and euthyroid multinodular goiter 2
- Monitoring the effectiveness of treatment and adjusting the dose as needed 5
Special Considerations
There are several special considerations to keep in mind when performing a thyroid radioactive uptake and scan, including:
- The need to exclude exogenous iodine overload before testing 2
- The potential for false negatives or false positives due to various factors, such as thyroid disease or other medical conditions 3
- The importance of using a reliable and accurate method for measuring thyroid uptake, such as a gamma camera-based method 4
- The potential benefits and limitations of using a collar detection device, such as the COTI, to provide real-time quantitation of thyroidal radioiodine uptake 5