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Dynamic ¹³N-Ammonia PET: A New Imaging Method to Diagnose Hypopituitarism

¹ Department of Nuclear Medicine, Guangdong Provincial People’s Hospital, Guangzhou, China
² Department of Nuclear Medicine, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China

We have developed a new imaging method to evaluate the blood perfusion and ammonia metabolism of the pituitary gland, and we preliminarily assessed its role in the diagnosis of hypopituitarism. Methods: Six female healthy volunteers (age range, 20–46 y) and 6 female patients (age range, 23–42 y) were enrolled in this study. Dynamic ¹³N-NH₃ PET was performed. Time-activity curves for the pituitary gland and internal carotid artery were generated by setting regions of interest on the transverse planes of the pituitary gland. The standardized uptake value of the pituitary gland, the radioactive ratio of pituitary to thalamus (P/T), and the first-pass uptake rate of ammonia in the pituitary gland were calculated. Results: ¹³N-Ammonia was extracted rapidly by pituitary tissue in the first 120 s after injection and trapped in pituitary tissue in the healthy volunteers. Three to 20 min after injection, the pituitary gland was clearly seen in the healthy volunteers, and the mean (±SD) size of the pituitary gland on ¹³N-ammonia PET images was (1.09 ± 0.17 cm) x (1.08 ± 0.14 cm) x (1.12 ± 0.09 cm). However, in patients with hypopituitarism, the first-pass uptake rate of ammonia in the pituitary gland was significantly lower than that in healthy volunteers (0.35 ± 0.10 vs. 0.75 ± 0.07). On images of patients, the pituitary gland was absent or could not clearly be found, was small or malformed, and showed significantly lower uptake of ¹³N-NH₃ than in healthy volunteers (standardized uptake value, 1.15 ± 0.34 vs. 3.74 ± 1.44; P/T, 0.65 ± 0.23 vs. 1.24 ± 0.34). Conclusion: Dynamic ¹³N-ammonia PET can provide information on blood perfusion and metabolism of the pituitary gland and is useful in early monitoring of damage to the pituitary gland and in diagnosing hypopituitarism.

Key Words: hypopituitarism • ammonia • PET

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