Comparison of 99mTc and 131I scans in thyroid function studies.

Thyroid function was studied in 170 patients, using technetium-99m (99Tc) and oral radio-iodine (131I); 110 patients had normal thyroid function, and 60 had hyperthyroidism. The 20-minute 99mTc uptake gave an accurate assessment of thyroid function in 95% of patients, and the 24-hour 131I uptake was accurate in 92%. One hundred 99mTc and 131I scintiscans were compared by 3 observers. Scans obtained with each isotope were of comparable quality, and in only 1 patient were both scans of poor quality. 99mTc is as good as 131I for assessing thyroid function and morphology, but has several advantages over 131I.