Pituitary uptake of [111In-DTPA]-octreotide is highly variable, and no formal methods for quantification have been described. Conflicting results have therefore been published as to the presence of somatostatin receptors in nonsecreting adenoma of the pituitary gland. The aim of the present study was to define the most accurate method for the analysis of [111In-DTPA]-octreotide SPECT studies of the pituitary gland.
Methods: We used a multidetector brain SPECT camera to measure pituitary uptake of [111In-DTPA]-octreotide in healthy volunteers and patients with and without pituitary adenoma. For quantification, two methods were compared, one involving a manually drawn ROI and one a fixed ROI, as to their reliability and discriminative power. The optimal time interval after injection was also studied in the volunteers.
Results: Optimal images were obtained 24 hr after injection. Correction for background activity is not useful in view of the very low counts at that time which result in highly fluctuating ratios. Lower variability was observed in the fixed ROI method in which activity was expressed as counts corrected for dosage and body weight.
Conclusion: A fixed ROI method without background correction is the most reliable way to measure pituitary uptake of [111In-DTPA]-octreotide. This method allows for good separation of somatostatin-receptor-positive adenomas from normal pituitary glands.