Thyroid scanning is a non-invasive imaging technique that observes the morphology and function of thyroid tissue using radioactive isotopes or ultrasound technology. It is primarily used to assess the benign or malignant nature of thyroid nodules, diagnose hyperthyroidism, and monitor treatment effectiveness. This examination can simultaneously provide information on anatomical structure and metabolic activity, making it an essential tool in thyroid disease diagnosis.
The procedure is generally divided into two categories: "Radioactive Isotope Scanning" and "Ultrasound Scanning," selected based on clinical needs. Radioactive isotope scanning requires injection of a small amount of radioactive material, while ultrasound scanning involves no radiation exposure. Each has different clinical applications.
Radioactive isotope scanning uses tracers such as Technetium-99m or Iodine-123. After intravenous injection, the tracer is absorbed by thyroid cells. Gamma cameras track the distribution of radiation to evaluate tissue metabolic activity. Areas of high concentration may indicate hot nodules, while areas of low concentration indicate cold nodules, aiding in lesion characterization.
Ultrasound scanning employs high-frequency sound waves reflected to produce images, allowing detailed visualization of the thyroid’s shape, size, and nodule structure. Combining real-time imaging with ultrasound-guided biopsy enables assessment of cystic versus solid components and surrounding tissue invasion. These two techniques are often used together to improve diagnostic accuracy.
Primarily used for evaluating hyperthyroidism (such as Graves’ disease), benign or malignant thyroid nodules, and postoperative follow-up of thyroid cancer. When blood tests show abnormal TSH levels or palpable enlargement, scanning provides functional tissue information to assist diagnosis.
For patients suspected of having autonomous hyperfunctioning nodules (such as toxic multinodular goiter), scanning can localize the lesion. Additionally, for those on long-term antithyroid medication, scanning can evaluate the medication’s effect on thyroid tissue.
Fasting for 4 hours before radioactive isotope scanning is required, and iodine-containing medications should be discontinued 2 weeks prior. After tracer injection, patients rest for 30 minutes, then lie down for about 20 minutes of scanning. The dose is controlled within safe medical limits, with a single scan dose equivalent to about three X-ray exposures.
Ultrasound scanning requires no special preparation, taking approximately 15-30 minutes. The physician uses a high-resolution probe to scan the neck, and elastography or fine-needle aspiration may be performed if necessary. Both thyroid lobes and cervical lymph nodes are included in the scan range.
The main advantage is the simultaneous assessment of structure and function, such as differentiating hot and cold nodules based on metabolic features. Radioactive isotope scanning is particularly effective for detecting metastatic thyroid cancer, while ultrasound can precisely measure nodule size and morphological changes.
The side effects of radioactive isotope scanning are extremely low, with possible redness or swelling at the injection site (<1%). Long-term follow-up studies show that the cancer risk from a single scan is negligible. Pregnant women are generally advised against this procedure due to fetal radiation sensitivity.
Ultrasound scanning is completely risk-free but should be performed by experienced physicians to avoid false negatives caused by technical errors. Those allergic to radioactive substances should opt for non-radioactive alternatives.
Contraindications include pregnancy, breastfeeding, and allergy to radioactive drugs. Iodine-containing agents (such as seaweed products) and antithyroid medications should be discontinued 2 weeks before the scan. After radioactive isotope administration, contact with children should be minimized to reduce secondary radiation exposure.
Patients with severe renal impairment may experience prolonged radioactive substance metabolism and should have adjusted examination intervals. It is important to inform the physician if prior radioactive treatments or scans have been performed to avoid excessive cumulative dose.
Radioactive isotope scanning may affect thyroid function tests, with TSH levels potentially abnormal within one week post-examination. Patients should inform other healthcare providers to prevent misdiagnosis. The interval between iodine-131 therapy and scanning should be at least 6 weeks to ensure tracer clearance.
Ultrasound does not interact with other imaging modalities, but scan order should be coordinated. If biopsy is required, it should be performed immediately after the scan to ensure accurate localization.
Multiple studies confirm that radioactive isotope scanning has over 90% accuracy in identifying metastatic thyroid lesions, while the ultrasound-based Thyroid Nodule Risk Stratification System (such as ATA guidelines) can accurately assess malignancy risk. Combining both methods can increase diagnostic sensitivity to 95%.
For hyperthyroid patients, scan results can guide treatment strategies: hot nodules are suitable for radioactive iodine therapy, while cold nodules are often recommended for surgical removal. Long-term follow-up studies show this approach can reduce misdiagnosis rates by 20%.
If patients cannot undergo radioactive scans, high-resolution ultrasound combined with elastography can be used. Blood tests such as TSH and TgAb can assist in functional assessment but cannot replace imaging for anatomical details.
Positron Emission Tomography (PET-CT) can be used in specific cases for thyroid cancer follow-up, though it is more expensive and involves higher radiation doses. MRI offers advantages in assessing extrathyroidal extension but requires longer examination times.
Yes, it is generally necessary to avoid iodine-rich foods (such as seaweed) and certain medications (like iodine-based contrast agents) before the thyroid scan. The physician will provide a 7 to 14-day preparation plan based on the type of tracer used to ensure clear and accurate imaging. Patients should inform their doctor of all medications they are taking before the scan to determine if any should be temporarily discontinued.
Will the procedure cause discomfort or high radiation exposure risk?The procedure is painless, requiring only lying still for gamma camera scanning for about 20-60 minutes. The radiation dose used is very low, posing no health risk to adults, but pregnant or breastfeeding women should avoid this examination. If anxiety occurs after tracer injection, patients can discuss calming measures with staff beforehand.
Are there special precautions or recovery steps after the scan?There is no need for special recovery; however, after injection of radioactive medication, it is recommended to drink plenty of water within 24 hours to promote metabolism and excretion, and to avoid close contact with pregnant women or infants. If neck swelling, fever, or other abnormal symptoms occur, immediate medical evaluation is advised.
What is the difference between thyroid scan results and ultrasound findings?Thyroid scans (nuclear medicine) reveal the metabolic activity of the thyroid, useful for determining benign or malignant tumors or abnormal metabolic regions. Ultrasound provides structural information, and both are often used together for comprehensive assessment. The physician will choose the most appropriate combination based on symptoms.
What factors might affect the accuracy of the scan?Recent high iodine intake (such as kelp or iodine-containing lozenges), use of antithyroid drugs, or prior radioactive treatments can interfere with scan results. Full disclosure of medical history and medications before the scan is essential to ensure reliable outcomes.
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