Optimal imaging time for delayed images in the diagnosis of abnormal parathyroid tissue with Tc-99m sestamibi.

PURPOSE: Double-phase scintigraphy with Tc-99m sestamibi is a good method to detect hyperfunctioning parathyroid glands. This study tried to determine the best time for delayed images: 2 or 4 hours.

METHODS

Fifty-six patients were studied, and 35 of them had primary hyperparathyroidism (mean age, 53 +/- 13 years; 54% were women). Cervical ultrasonography was performed on 29 of 56 (52%) patients and surgery in 16 of 56 (29%) patients. The dose was 740 MBq (20 mCi) given intravenously, and the acquisition was performed at 10 minutes, 2 h, and 4 h using anterior views, including the mediastinum. Studies that had positive results were analyzed blindly by two independent observers, who selected the best definition for abnormal activity.

RESULTS

Nineteen of 56 (34%) studies were negative and 37 of 56 (66%) were positive, 25 of them with one focus and 12 with two or more parathyroid foci. Analysis revealed 76% agreement between the observers (the rest was classified by consensus). In 70% of the cases, the best delayed image was obtained at 2 hours, in 16% at 4 hours (P < 0.00001), and in 14% both images were similar. In those cases with better images at 4 hours, the 2-hour images also showed the lesions. In two patients, lesions were seen only at 2 hours. These results could be explained by tracer decay, washout of parathyroid activity, or both.

CONCLUSIONS

The best protocol should include the early 10-minute image and the 2-hour delayed view. Further controls do not appear necessary. This may be important for patient throughput.