Tc-99m diphosphonate imaging in the differential diagnosis of thyroid nodules

Early Tc-99m diphosphonate (DP) imaging was performed in 122 patients with cold thyroid nodules in an effort to differentiate benign nodules from malignant. Immediately upon completion of the routine 24-hour I-123 uptake and multiview pinhole imaging, Tc-99m DP was injected intravenously and three serial 3-minute anterior images of the thyroid gland were obtained. Follow-up information was available in 85 patients. All cystic lesions had less Tc-99m uptake as compared with the uptake in the normal parts of the thyroid. However, 48 of 50 solid nodules had Tc-99m DP uptake to the same or greater degree than did the normal gland. The other two had mixed pattern on ultrasound examination. Most of the carcinomas (8 of 10) and benign adenomas (15 of 22) had identical appearance on Tc-99m scans, i.e., uptake in the lesion being the same as in the normal thyroid. It appears that by using this technique it is possible to separate solid nodules from cystic, but not benign from malignant.