To assess the value of 99mTc-pertechnatate-MIBI subtraction technique, SPECT-MIBI in comparison to standard Planar MIBI dual phase scintigraphy in suspected patients of hyperparathyroidism.
This study cohort includes 33 patients who were referred to the department of nuclear medicine as suspected case of hyperparathyroidism for detection and localization of abnormal parathyroid gland. 23 cases were referred with primary diagnosis of primary hyperparathyroidism, two patients of suspected recurrent parathyroid adenoma and 8 cases were secondary hyperparathyroidism due to end stage renal disease. Imaging consisted of 99mTc-pertechnetate planar images of the neck followed by 99mTc-sestamibi planar images of the neck and and chest (early images) at 5 min,10 min and 15 min. SPECT images of the neck and chest were obtained soon after planar image (early images). Delayed images of neck and chest was acquired at 120 min. The thyroid count in pertechnetate is normalized to those in the 99mTc MIBI image and subtraction was done from the corresponding delayed 120 min image. A positive MIBI scan for parathyroid adenoma was defined as an area of increased focal uptake which persisted on late imaging, contrary to the uptake in the normal thyroid tissue which progressively decreases over time (differential washout). All the patients has undergone ultrasonography of neck also.
The sensitivity for abnormal parathyroid glands in primary hyperparathyroidism by dual phase planar images was 70% in early phase and 80%in late phase, 80% in double-phase (early and late) sestamibi images; 80% in subtraction imaging and 90% in SPECT imaging. Overall sensitivity for parathyroid adenomas was 93.33%. while the sensitivity for Ultrasonography was 73.33% only. True localization of abnormal parathyroid gland was 79% for MIBI imaging while 36% for Ultrasonography. True localization was done with oblique image was 70%, early 57%, delayed 62.5% SPECT 89% and subtraction 71%. MIBI could not localize abnormal parathyroid gland in hyperplasia
Early SPECT is better method than dual phase planar and subtraction technique for detection and localization of abnormal parathyroid gland. Double-phase sestamibi imaging was equally sensitive to subtraction technique, so baseline thyroid imaging with pertechnetate may not be necessary in all patients.
