A comparative study of 99mTc and 131I in thyroid scanning

Area of Science:

• Nuclear Medicine
• Radiology
• Endocrinology

Background:

• Thyroid nodules are common, and accurate diagnostic imaging is crucial for management.
• Traditionally, both 99mTc pertechnetate (99mTcO4) and radioactive iodine (131I) have been used for thyroid scintigraphy.
• Determining the optimal imaging agent for evaluating palpable thyroid nodules is essential.

Purpose of the Study:

• To compare the diagnostic utility of 99mTcO4 and 131I thyroid scans in patients with palpable thyroid nodules.
• To assess whether 131I scanning remains a necessary procedure in the diagnostic workup of thyroid nodules.
• To evaluate the role of 99mTcO4 scintigraphy as a primary imaging modality.

Main Methods:

• A comparative study involving 46 patients with palpable thyroid nodules.
• Thyroid scintigraphy was performed using both 99mTcO4 and 131I in all participants.
• Discrepancies between the two imaging modalities were analyzed, and findings were correlated with surgical pathology.

Main Results:

• A discrepancy between 99mTcO4 and 131I scans was observed in only three patients (6.5%).
• One case of malignancy was detected where the nodule showed 99mTcO4 uptake but not 131I uptake.
• In two cases, nodules 'cold' on 99mTcO4 were 'hot' on 131I and proven benign.
• 99mTcO4 offers a lower radiation dose and greater convenience compared to 131I.

Conclusions:

• 99mTc pertechnetate (99mTcO4) scintigraphy is recommended as the initial imaging modality for palpable thyroid nodules due to its safety profile and convenience.
• Radioactive iodine (131I) scanning may be reserved for cases where 99mTcO4 scans show nodules with equal function to surrounding tissue, to further evaluate for potential malignancy.
• This approach can optimize diagnostic accuracy while minimizing radiation exposure.