Percent Uptake of¹³¹I Radioactivity in the Adrenal from Radioiodinated Cholesterol

Abstract

Ten patients, four with Cushing's syndrome and six with “normal” adrenal function, were studied to determine the percent uptake of 131I radioactivity in their adrenal glands following administration of a dose of 131I-19-iodocholesterol. This was accomplished with an Anger gamma camera, a multichannel analyzer and a PDP-8L computer. Net counts in the adrenal regions of the patients were related to μCi of 131I radioactivity by referring to a standard curve. This curve was constructed from a study in which known quantities of Na131I were placed in small vials and counted at different depths in a tissue equivalent simulated body phantom. A method for determining adrenal depth in the patient from a lateral view was developed by relating the distance between a radioactive marker on the patient's back and the adrenal to the number of matrix points between the centers of the images on the multichannel analyzer oscilloscope picture. All four patients with Cushing's syndrome had percent uptakes of 131I radioactivity in their adrenals greater than the six patients with “normal” adrenal function. The patient with the lowest percent uptake in the Cushing's group was receiving 1-(o-chlorophenyl)-1-(p-chlorophenyl)-2,2-dichloroethane (o,p′-DDD) at the time of administration of the radioiodocholesterol; however, her percent uptake was significantly greater than the “normals.” Adrenal tissue, surgically removed from two patients in whom the percent uptake had been determined in vivo, had in vitro tissue radioactivity assays which were within 15% of the in vivo value in one case and 25% in the other. The percent uptake of 131I radioactivity from radioiodocholesterol appears to be a safe and reproducible test of the functional status of the adrenal cortex. The data suggest that hyperfunctioning adrenal cortices can be differentiated from normally functioning adrenal cortices by an external counting method.