Quantitation of iodine-123 MIBG uptake by normal adrenal medulla in hypertensive patients.

Eighteen hypertensive patients with a clinical suspicion of pheochromocytoma and raised or borderline raised plasma catecholamine and urinary vanillyl mandelic acid (VMA) levels were studied by scintigraphy using 123I-labeled metaiodobenzylguanidine (MIBG). None of these patients had any scintigraphic evidence of pheochromocytoma at the time of study or on subsequent clinical follow-up. A quantitative approach was taken to calculate the adrenal medullary uptake of [123I]MIBG in these patients. Three different methods of quantitation were evaluated using data acquired from an anthropomorphic phantom and analysed by three independent observers. In the patient studies 34 out of 35 adrenal medullas were visualized with uptake in the range of 0.01-0.22% of the administered dose 22 hr postinjection which was calculated using the preferred quantitation method. This is an appropriate control group range for comparison with patients who have proven norepinephrine and epinephrine secreting tumors. A quantitative approach to [123I]MIBG imaging provides an important tool for studying adrenomedullary pathophysiology.