This is a detailed testing protocol for a Pertechnetate thyroid scintigaphy test for patients with suspected thyroid and parathyroid pathology.
Radiopharmaceutical
Technetium-99m pertechnetate (Tc-99m Pt)
Concept
Tc-99m Pt is absorbed from the bloodstream into the thyroid gland without organification. The principle of pertechnetate (Tc-99m Pt) absorption by thyroid cells is based on the thyroid gland's active uptake and transport of iodide. The thyroid gland has a unique ability to concentrate iodide, an essential process for synthesizing thyroid hormones. This property of the thyroid gland is exploited in thyroid scintigraphy using Tc-99m pertechnetate.
Technetium-99m pertechnetate is a radioactive tracer that behaves similarly to iodide in the body. The thyroid gland absorbs it, but unlike iodide, Tc-99m Pt does not undergo organification (incorporating iodide into thyroid hormones). This difference means that Tc-99m Pt is only trapped by the thyroid gland and not used in hormone synthesis.
The process of pertechnetate absorption by thyroid cells involves the sodium-iodide symporter (NIS), a membrane protein located on the basolateral surface of thyroid follicular cells. NIS transports iodide (and pertechnetate) from the bloodstream into the thyroid cells against a concentration gradient. This active transport is driven by the sodium gradient maintained by the Na+/K+ ATPase pump.
Mitochondria play a crucial role in thyroid cells' overall function and energy metabolism, but their role in the pertechnetate uptake process is indirect. Mitochondria generate ATP (adenosine triphosphate), the primary energy source for various cellular processes, including the activity of the Na+/K+ ATPase pump. The Na+/K+ ATPase pump maintains the sodium gradient, essential for properly functioning the sodium-iodide symporter (NIS). Thus, mitochondria are essential for providing the energy needed for the active transport of iodide and pertechnetate into the thyroid cells.
Methodology
Patient Preparation
No specific preparation required.
- No fasting necessary
- No thyroid hormone withdrawal required
- Minimal impact from other medications
- Unaffected by recent iodine contrast procedures
- Special considerations for breastfeeding patients, children, and potential fetal exposure
Dosage
Administer 74–200–370 MBq/patient of Tc-99m Pt, obtained from a Tc-99m generator, following quality control regulations.
Dose Calibration: Ensure proper dose calibration.
Injection: Administer intravenously (IV).
Wait Time
Allow 15–30 minutes post-injection before imaging.
Patient Positioning: Place the patient supine with a slight neck extension.
Gamma Camera
- Ensure daily calibration and valid quality control tests
- Use a small-field rectangular/pinhole collimator or a low-energy high-resolution (LEHR) collimator
Image Acquisition: Capture anterior-posterior (AP) images over the patient's neck, as close as possible to avoid resolution interference due to inadequate distance. A distance of 10 cm from the neck provides a magnification factor of 2–2.5.
Image Processing: No specialized PC programs are needed. Additional software may be used to analyze counts in different regions of interest (ROI). Image interpretation criteria are detailed below.
Clinical Applications
- Diagnosing hyperthyroidism in various conditions
- Diagnosing hypothyroidism in primary and secondary forms
- Detecting thyroid cancer (cold nodule)
- Identifying thyroiditis, cysts, and other nodule causes
- Assessing thyroid anatomical variations
Additional Examinations that may be required (supportive findings)
- Clinical examination
- Thyroid ultrasound
- Blood tests (e.g., TSH, FT4, FT3, anti-TPO antibodies, anti-Tg, calcitonin, thyroglobulin, TRab, etc.)
- Fine needle aspiration biopsy (FNAB)
Considerations
Thyroid scintigraphy is well-established in evaluating thyroid diseases, particularly thyroid nodules, as evidenced by national and international diagnostic and treatment algorithms.
Reporting
The report should include patient identification data, institutional information, and physician details. It should also contain technical data on the radiopharmaceutical, dosage, gamma camera, and acquisition data. The estimated absorbed dose from the examination should be noted.
The report will describe the thyroid's shape, position, size, contour, presence or absence of nodules, and distribution of radiotracer in the gland, lobes, and nodules. Any unusual findings on scintigraphy will also be mentioned.
Interpretation of Thyroid Scintigraphy
The normal thyroid scan with Tc-99m Pt will reveal the following characteristics:
- The typical "butterfly" shape of the thyroid gland.
- Normal dimensions that adhere to laboratory standards, taking into account area-specific particularities and age-related variations.
- Positioning in the anterior neck area, above the sternal notch and in the region of the thyroid cartilage.
- Regular contour without any interruptions or mismatches.
- Homogeneous distribution of the radiotracer, with intense color in the center of each lobe corresponding to the thickness of the thyroid tissue. The margins will display a less intense color due to the decreasing amount of thyroid tissue.
- Absence of nodules with different metabolic activities.
- Note that it is normal for the right lobe of the thyroid gland to be larger than the left one. The salivary glands may also be visible on the scan.
Abnormal Thyroid Scans
Scintigraphy can help identify various thyroid conditions based on the characteristics observed in the scan. These may include:
- Hyperthyroidism: Increased radiotracer uptake in the thyroid gland, suggesting overactive thyroid function.
- Hypothyroidism: Decreased radiotracer uptake in the thyroid gland, indicating underactive thyroid function.
- Thyroid nodules: Presence of nodules with varying radiotracer uptake, which may be classified as "hot" (hyperfunctioning) or "cold" (hypofunctioning) nodules.
- Thyroiditis: Heterogeneous radiotracer distribution and possible areas of decreased uptake, reflecting inflammation.
- Thyroid cancer: A "cold" nodule suggests a non-functioning area within the thyroid gland that may be malignant.
- Thyroid anatomical variations: Scintigraphy can reveal retrosternal goiter, sublingual thyroid, lateral-cervical thyroid, accessory lobe (Lalouette's pyramid), and agenesis of a lobe or the entire gland.
Conclusion
Thyroid scintigraphy using Tc-99m Pt gamma camera is a valuable tool in diagnosing and evaluating various thyroid conditions, including hyperthyroidism, hypothyroidism, thyroid nodules, and anatomical variations. It is essential to conduct additional examinations, such as clinical evaluations, thyroid ultrasounds, and blood tests, to corroborate scintigraphy findings and ensure a comprehensive assessment of the patient's thyroid health.
Reference
Ramos CD, Zantut Wittmann DE, Etchebehere EC, Tambascia MA, Silva CA, Camargo EE. Thyroid uptake and scintigraphy using 99mTc pertechnetate: standardization in normal individuals. Sao Paulo Med J. 2002 Mar 7;120(2):45-8. doi: 10.1590/s1516-31802002000200004. PMID: 11994772.
Kindly Let Us Know If This Was helpful? Thank You!
