Dual-phase 99mTc-sestamibi imaging and dual isotope imaging: Its utility to improve localization of parathyroid adenoma

Objectives Dual-phase 99mTc-sestamibi (methoxyisobutylisonitrile [MIBI]) is the technique of choice for hyperparathyroidism, especially for localizing parathyroid adenomas. Apart from dual-phase we can also use dual-isotope 99mTc-sestamibi and 99mTc-pertechnetate for comparison of thyroid and parathyroid images.

Methods Anterior neck and upper thorax images acquired with low energy high resolution pin-hole collimator at 20 min and 2hr after 99mTc-sestamibi injection, and then 99mTc-pertechnetate injected and anterior neck images acquired with same collimator. The results were analyzed retrospectively for hyperplasia, adenoma, or normal parathyroid by persistence of activity in 2 or more foci, a solitary focus, or no activity on delayed images. The dual-isotope images were used for visual comparison for activity in thyroid at various stage images.

Results The study included 30 patients from Jan 2012 to Sep 2012. A positive MIBI scan for parathyroid adenoma was defined as an area of increased focal uptake which persists on delayed imaging, contrary to the uptake in the normal thyroid tissue which progressively decreases over time and with injection of 99mTc-pertechnetate only thyroid gets activity and parathyroid does not get activity.

Conclusions Dual-phase 99mTc-MIBI imaging is more sensitive and specific for parathyroid hyperplasia. It is very much supportive to localize hyperplastic glands pre-operatively which guide in resection. A thyroid ratio between immediate and delayed images will help distinguish hyperplasia from normal parathyroid in uncertain cases.