Comparison of ^99mTc Pertechnetate Thyroid Uptake Rates by Gamma Probe and Gamma Camera Methods for Differentiating Graves' Disease and Thyroiditis

Background: Technetium-99 m (^99mTc) pertechnetate thyroid uptake rate can be measured with a gamma probe or gamma camera. This study was performed to compare their diagnostic accuracy for evaluating patients with thyrotoxicosis.

Methods: We retrospectively reviewed ^99mTc pertechnetate thyroid uptake rate records of patients by both gamma probe and camera methods at a tertiary center in Korea from November 2019 to June 2020. We determined the normal reference ranges of thyroid uptake rate by two methods and compared both methods for differentiating Graves' disease and thyroiditis in patients with thyrotoxicosis by receiver operating characteristic curve analysis.

Results: A total of 371 patients (euthyroid 89, Graves 167, and thyroiditis 115) were included. The normal reference range for thyroid uptake rate in euthyroid patients was 0.3-1.9% and 2.0-4.7% for the camera and probe methods, respectively. For differentiating Graves' disease and thyroiditis, the area under the curve of the camera method (0.988) was significantly greater than that (0.975) of the probe method (p = 0.030). The sensitivity and specificity for the probe method were 92.2% and 91.3%, respectively, with a cut-off value of 3.0%. Those for the camera method were 93.4% and 94.8%, respectively, with a cut-off value of 0.7%.

Conclusion: ^99mTc pertechnetate thyroid uptake rate measured by the camera method had higher diagnostic accuracy than the probe method for evaluating patients with thyrotoxicosis. Considering the diagnostic accuracy and patient convenience, the thyroid uptake rate measured by the camera method would be a good substitute for the probe method.