Some comparative studies using 99mTc and 131I in thyroid scanning

Area of Science:

• Nuclear Medicine
• Endocrinology
• Radiopharmacology

Background:

• Thyroid scintigraphy is crucial for evaluating goiter and nodules.
• Technetium-99m (99mTc) and iodine-131 (131I) are commonly used radioisotopes for thyroid imaging.
• Discrepancies in imaging findings can impact patient diagnosis and management.

Purpose of the Study:

• To compare the diagnostic accuracy of thyroid scans using 99mTc and 131I.
• To identify and analyze discrepancies between 99mTc and 131I thyroid scintigraphy in euthyroid goiter patients.
• To determine the clinical utility of 99mTc scintigraphy compared to 131I.

Main Methods:

• Retrospective analysis of thyroid scans from 40 euthyroid goiter patients.
• Comparison of scintigraphic findings obtained with 99mTc and 131I radioisotopes.
• Evaluation of nodule characteristics (e.g., "warm" vs. "cold") between the two imaging modalities.

Main Results:

• Significant discrepancies in thyroid scan interpretations were observed in 20% of patients.
• Examples include "warm" nodules on 99mTc scans appearing "cold" on 131I scans, and vice versa.
• Discrepancies are attributed to differences in radioisotope metabolism and imaging timing.

Conclusions:

• Routine use of 99mTc thyroid scintigraphy in adults is not recommended due to potential discrepancies.
• 99mTc scans may be useful only when 131I scans are illegible.
• "Cold" nodules identified on 99mTc scans warrant re-evaluation, potentially after T3 stimulation.