Production, formulation, module design and quality control of [13N]NH3 for future PET studies in Iran

Improvements in positron emission tomography (PET) have engaged many research groups to prepare different radiopharmaceticals following administration to humans. [13N]NH3 is probably the only clinically used nitrogen-13 radiotracer (positron energy=0.64 MeV, tissue range=2.4 mm, half-life=109.7 min). Its short half life can be an advantage. We have been interested in the preparation and quality control of PET radiopharmaceuticals in the country for ultimate use in clinics. In this study, one of the most simplest routes of production, i.e. irradiation of natural high-purity water by protons followed by catalytic reduction, has been targetted as well as manufacture of a prototype [13N]NH3 production module. EXPERIMENTAL - Selection of the production parameters -In this research, 16O(p,α)13N was selected as the best nuclear reaction for the production of 13N, using natural water as the target material, due to the small amount of O-18 resulting in fluorine-18 that could be easily separated by physical methods and also for cost-effectiveness. Preparation of [13N]-Nitrate/nitrite anions: Nitroxy anions were prepared by 18 MeV proton bombardment of a DDH2O sample (1.7 ml). The sample was irradiated for 15-20 min by 18MeV protons in an all-silver target in a 30 MeV cyclotron at NRCAM. Cooling was performed using a pressurized flow of He gass. Radiochemical purity of [13N]NH3-Radio thin layer chromatography was performed using a mixture of acetone-propionic acid-staurated brine (1:2:4). NO3 and NO2 anions eluted at Rf of 0.45. Thus, the radiochemical yields (more than 98% in each case, n=9) were determined by comparison of NO3 and NO2 and the major radio peak at Rf0.80 for 13N-NH3. Conclusion [13N]NH3 was prepared by 18 MeV proton bombardment of the natO target. The target was bombarded with a current intensity of 8μA for 20 minutes (13.5 ±0.5 μAh). The chemical conversion of NOx anions into NH4+ cation was performed using an in-house made DeVarda's catalyst at our center. The possibilty of the formation of various radionuclidic impurities was considered using nuclear codes. The chemical purity was checked using colorimetric assay. The chemical separation process was based on a distilation method. The resulting activity of [13N]NH3 was 10-20 mCi at the end of bombardment (E.O.B.) and the production yield was 5mCi/μAh