RT Journal Article SR Electronic T1 Feasibility of 13N-ammonia production by 13C(p,n)13N reaction on a 7.5 MeV cyclotron JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 663 OP 663 VO 59 IS supplement 1 A1 Gregory Nkepang A1 Hailey Houson A1 Hariprasad Gali A1 Vibhudutta Awasthi YR 2018 UL http://jnm.snmjournals.org/content/59/supplement_1/663.abstract AB 663Objectives: 13N-ammonia is commonly produced using 16O(p, α)13N reaction but one of the limiting factor of this reaction is the relatively small reaction cross-section at proton energies of <10 MeV. An alternative N-13 ammonia production method using 13C(p,n)13N reaction is more suitable for a preclinical or small PET imagining facility equipped with a <10 MeV cyclotron which has a higher cross-section can be used. We report a novel practical and single-step method for the production of 13N-ammonia using 10% 13CH3OH/H2O solution target on a 7.5 MeV ABT BG-75 cyclotron. Methods: A solution (80 µl capacity) target constructed with tantalum consisting of a havar window supplied by ABT Molecular Inc for the production of 18F-fluoride was used without any modifications. Optimization of the reaction parameters was made thus; target solutions of various percentages of methanol (13C, 99% enrichment) solution were made with Milli-Q type 1 Ultrapure water and used to obtain maximum 13N-ammonia dose after bombardment. Target currents ranging from 0.5-2.5 µA were used as well as various bombardment times (2.0-10 min) were also investigated. Half-life determination and USP-monographed ion exchange analytical HPLC were used to identify the radionuclide. After the bombardment, an injectable solution was prepared by making it isotonic and filtering it through a 0.2 µm syringe filter. Doses were also assayed for the presence of methanol by gas chromatography (GC). Small animal PET/CT imaging was conducted in CD-1 mice (20-30 g) at 5 min after injection of 13N-ammonia (~8 MBq). Results: The product yield varied between 14.8-180.2 MBq, with decay correction, depending on the target current and duration of bombardment. Not much difference in the yield was observed with increased percentage of methanol (13C) in the target solution. A maximum yield of 180.2 MBq was obtained after a 10 min bombardment at a target current of 2.4 µA. We maintained target current at <3.0 µA to avoid charring and evaporation of the methanol present in the target solution. Even then, evaluation of target after multiple bombardments showed significant charring of organic material, which might have been responsible for an observed reduction in yields during later bombardments. The half life of 10 min confirmed the 13N radionuclide, while the radio-HPLC retention time of 5.37 min confirmed the 13N-NH4+. The methanol content in the injected dose was not indistinguishable from water by GC. PET/CT images indicated the accumulation of 13N-ammonia in myocardial tissue. Other organs such as liver, kidney, and bladder also demonstrated the presence of activity in accordance with reported bio-distribution of 13N-ammonia. Conclusion: This work demonstrates the proof-of-principle for operationally simple method to produce 13N-ammonia from 13CH3OH in one step using a low energy cyclotron. The yields are low, but adequate for preclinical use. Efforts are currently underway to further increase the yield.