Comparison of 99mTc and 123I for thyroid imaging

Area of Science:

• Nuclear Medicine
• Diagnostic Imaging

Background:

• Prior radiotherapy increases the risk of thyroid neoplasms.
• Effective imaging techniques are crucial for early detection in high-risk populations.

Purpose of the Study:

• To compare the diagnostic utility of technetium-99m (99mTc) and iodine-123 (123I) for thyroid imaging in patients with a history of radiotherapy.
• To evaluate the advantages and disadvantages of each radionuclide for routine and specific clinical scenarios.

Main Methods:

• Thyroid imaging was performed on 85 patients using both 99mTc and 123I with a scintillation camera and pinhole collimator.
• Patients were selected from a larger cohort with a history of radiotherapy and predisposition to thyroid neoplasms.
• Image comparison focused on information content, contrast, focal abnormalities, and imaging time.

Main Results:

• 99mTc and 123I provided similar diagnostic information in 66 out of 85 patients.
• Disparities were observed in 19 patients, with 11 showing increased 99mTc uptake not visible with 123I.
• 123I offered slightly better contrast but required longer imaging times; 99mTc sometimes detected abnormalities more readily.

Conclusions:

• Currently, 123I does not offer significant advantages over 99mTc for routine thyroid imaging.
• 123I is recommended for patients with very poor thyroid function or suspected retrosternal thyroid tissue.
• Areas of increased 99mTc uptake warrant further investigation with 123I.