PARATHYROID IMAGING USING SIMULTANEOUS DOUBLE-WINDOW RECORDING OF TECHNETIUM-99M-SESTAMIBI AND I-123

Technetium-99m-sestamibi represents an important advance in the scinti graphic location of parathyroid neoplasms. However, the optimal proced ure for Tc-99m-sestamibi parathyroid scanning has not been defined. Th e first objective of this work was to optimize the technical aspects o f subtraction scanning, using simultaneous double-window recording of Tc-99m-sestamibi and I-123 instead of successive image recording. The second objective was to compare two protocols for detecting abnormal p arathyroid glands: subtraction scanning and single-tracer double-phase scanning. Methods: Thirty patients referred for first surgery of prim ary hyperparathyroidism had both subtraction scanning and double-phase scanning in the same imaging Session. Images of Tc-99m-sestamibi and I-123 were recorded simultaneously in nonoverlapping windows and then subtracted. For double-phase scanning, images of Tc-99m sestamibi, acq uired 15 min and 120 min after tracer injection, were visually compare d. Surgery disclosed a solitary adenoma in 27 patients, bilateral aden omata in 2 patients and 3 hyperplastic glands in the last patient. No patient had persistent hypercalcemia. Results: Preoperative Tc-99m-ses tamibi/I-123 subtraction scanning located 25 of 27 solitary adenomas, the bilateral adenomata and 3 of 3 hyperplastic glands. The overall se nsitivity for enlarged parathyroids was 94%, and the false-positive im age rate was 3%. The Tc-99m-sestamibi single-tracer technique located 22 of 27 solitary adenomas, the bilateral adenomata and 1 of 3 hyperpl astic glands. Overall sensitivity was 79% and the false-positive image rate was 10%. The gamma camera imaging time was 30 min for the subtra ction technique and 50 min for the single-tracer double-phase study. A n ectopic adenoma in the sheath of the right carotid artery was detect ed by both techniques. Conclusion: These results, together with other data in the literature, indicate that Tc-99m-sestamibi/I-123 subtracti on imaging is accurate in locating enlarged parathyroids. Classical di fficulties of this technique (motion artifacts and prolonged immobiliz ation) were avoided by using simultaneous recording of the two isotope s. In this series subtraction imaging was more rapid and more sensitiv e (p < 0.04) than the single-tracer technique.