Presurgical localization of abnormal parathyroid glands using a single injection of Tc-99m sestamibi: comparison of high-resolution parallel-hole and pinhole collimators, and interobserver and intraobserver variation.

PURPOSE: Scintigraphy using Tc-99m sestamibi is sensitive in localizing abnormal parathyroid glands in patients with hyperparathyroid disease (HPT). Various methods have been described to increase the sensitivity of the single-tracer technique, such as SPECT, factor analysis of dynamic structures, and use of a pinhole collimator, but often the gain in sensitivity is accompanied by a loss of specificity.

PURPOSE: In this study, the authors compared the sensitivity and specificity of side localization of the diseased gland(s) using the double-phase single-tracer method performed with and without the addition of a pinhole collimator in the early and late phases of imaging. The combined high-resolution parallel-hole and pinhole collimator imaging protocol was further validated by investigation of interobserver and intraobserver variation.

MATERIALS AND METHODS: Forty-seven patients with primary HPT and 16 patients with secondary HPT examined from 1996 to 1999 with the Tc-99m sestamibi double-phase technique and who had subsequent surgery formed the basis of the study. Their histologic and follow-up data were also factored into this analysis. Tc-99m sestamibi (750 to 900 MBq; 18.9 to 24.3 mCi) was injected. Ten-minute neck and mediastinum images acquiring 1,000 K counts were obtained with the high-resolution parallel-hole collimator, and a neck image containing 500 K counts was obtained with the pinhole collimator. Two to three hours later, the same parallel-hole and pinhole collimator images were obtained that had the same acquisition time as the early images. Two observers who were nuclear medicine specialists independently viewed all the parallel-hole scintigrams and afterward all parallel-hole and pinhole scintigrams two times.

RESULTS: Thirty-eight (81%) of the patients with primary HPT had a single adenoma. The sensitivity and specificity for the correct side of localization were 54% and 89%, respectively, using the high-resolution parallel-hole collimator, and 88% and 77%, respectively, with the addition of the pinhole collimator in all patients with primary HPT. In patients with secondary HPT, the sensitivity and specificity for localization of the correct side were 58% and 100%, respectively, using the high-resolution parallel-hole collimator, and 85% and 100%, respectively, with the addition of the pinhole collimator. The interobserver agreement was acceptable, with an overall agreement of 84% and a kappa value of 0.67. The intraobserver agreement was even better, with an overall agreement of 88% and 90% and kappa values of 0.76 and 0.79 for the two observers.

CONCLUSIONS: Sensitivity is increased considerably when the pinhole collimator is added to the imaging protocol of parathyroid scintigraphy in patients with primary or secondary HPT. A loss of specificity occurred only in patients with primary HPT. The precision of the combined approach is very high.