Abstract

Introduction and objective: Pinhole has been the main standard collimator to be used for thyroid imaging. There has been a gradually increasing trend to replace pinhole with the use of high-resolution low-energy parallel-hole collimator with zoom in thyroid imaging. The objective of this study is to compare parallel-hole collimator acquisition of thyroid gland with that obtained by pinhole collimator to find the effect on the diagnostic information in nodular thyroid disease.

Material and methods: A total of 29 patients, 24 women and 5 men, aged 18 to 70 years who were routinely referred for thyroid imaging for the assessment of nodular disease were studied. Each patient was injected with 185 MBq (5 mCi) of Tc-99m sodium pertechnetate intravenously. After 20 minutes, acquisition using pinhole followed by parallel-hole collimators was obtained. For pinhole acquisition, a 3-mm insert was used, and 3 images were obtained in the anterior and anterior oblique projections. For parallel-hole acquisition, anterior view was obtained for 250 K. The collimator was placed as close as possible to the patient. The image quality, number, and definition of nodules were evaluated by 2 independent, qualified nuclear medicine physicians. Differences were resolved by consensus.

Results: There were 14 patients who had nodular patterns and 15 had no apparent nodules. There were 40 nodules of different sizes detected by pinhole imaging. Only 10 (25%) of these nodules were observed on parallel-hole images.

Conclusion: Pinhole imaging must be used for thyroid imaging particularly in patients suspected of having nodular disease.