Parathyroid imaging using simultaneous double-window recording of technetium-99m-sestamibi and iodine-123

Technetium-99m-sestamibi represents an important advance in the scintigraphic location of parathyroid neoplasms. However, the optimal procedure for 99mTc-sestamibi parathyroid scanning has not been defined. The first objective of this work was to optimize the technical aspects of subtraction scanning, using simultaneous double-window recording of 99mTc-sestamibi and 1231 instead of successive image recording. The second objective was to compare two protocols for detecting abnormal parathyroid glands: subtraction scanning and single-tracer double-phase scanning.

Thirty patients referred for first surgery of primary hyperparathyroidism had both subtraction scanning and double-phase scanning in the same imaging session. Images of 99mTc-sestamibi and 123I were recorded simultaneously in nonoverlapping windows and then subtracted. For double-phase scanning, images of 99mTc-sestamibi, acquired 15 min and 120 min after tracer injection, were visually compared. Surgery disclosed a solitary adenoma in 27 patients, bilateral adenomata in 2 patients and 3 hyperplastic glands in the last patient. No patient had persistent hypercalcemia.

Preoperative 99mTc-sestamibi/123I subtraction scanning located 25 of 27 solitary adenomas, the bilateral adenomata and 3 of 3 hyperplastic glands. The overall sensitivity for enlarged parathyroids was 94%, and the false-positive image rate was 3%. The 99mTc-sestamibi single-tracer technique located 22 of 27 solitary adenomas, the bilateral adenomata and 1 of 3 hyperplastic glands. Overall sensitivity was 79% and the false-positive image rate was 10%. The gamma camera imaging time was 30 min for the subtraction technique and 50 min for the single-tracer double-phase study. An ectopic adenoma in the sheath of the right carotid artery was detected by both techniques.

These results, together with other data in the literature, indicate that 99mTc-sestamibi/123I subtraction imaging is accurate in locating enlarged parathyroids. Classical difficulties of this technique (motion artifacts and prolonged immobilization) were avoided by using simultaneous recording of the two isotopes. In this series subtraction imaging was more rapid and more sensitive (p < 0.04) than the single-tracer technique.