In vivo uptake of technetium-99M-sestamibi by parathyroid glands in comparison to surrounding tissues of the neck

Technetium-99M-sestamibi (Tc-99M-sestamibi) has recently been proven to be a sensitive and specific agent for imaging of parathyroid disease; however, the selective nature of its uptake by different tissues has not been investigated. Fifteen consecutive patients undergoing neck exploration for hyperparathyroidism were given 3 to 15 mCi of Tc-99M-sestamibi at various times before surgery, and at the time of exploration, samples of parathyroid tissue, blood, fat, muscle, and thyroid were taken from the neck. All samples were carefully weighed and counts of radioactivity were measured. Activity was normalized to counts per gram of tissue and counts of radioactivity were compared using a multiple range analysis of variance test. Mean counts per gram (±SE) in abnormal parathyroid tissue (adenomas and hyperplastic glands; 1.1 x 10⁶ ± 2.7 x 10⁶) were significantly higher than in any of the other tissues measured (P < 0.05); thyroid, 7.0 x 10⁴ ± 1.6 x 10⁴; muscle, 8.9 x 10⁴ ± 2.1 x 10⁴; fat, 2.1 x 10⁴ ± 4.2 x 10³; and blood, 9.8 x 10³ ± 2.3 x 10³. Mean ratios of counts (±SE) of abnormal parathyroid tissue to other tissues were found to be as follows: thyroid, 35.3 ± 12.6; muscle, 17.4 ± 6.2; fat, 80.7 ± 20.0; and blood, 161.0 ± 31.6. From these data, Tc-99M-sestamibi clearly exhibits significantly higher uptake in abnormal parathyroid tissue relative to other tissues measured in the neck. This increased uptake in parathyroid gland tissue accounts for the utility of Tc- 99M-sestamibi in localization studies for hyperparathyroidism. Quantification of in vivo uptake of Tc-99M-sestamibi may help refine techniques for improved localization of hyperfunctional parathyroid glands.