Production, quality control and initial imaging studies of [82mRb]Rb injection for PET studies

Rubidium-82m (HL: 6.5 h, Eβ+=0.80 MeV, E.C.=74%) is a rather long-half life PET radioisotope with a potential use in myocardial studies by PET which has not been regularly reported in nuclear medicine studies. Due to our recent works on the producion and quality control of some PET radiotracers in the country, we were interested in the production, formulation and administration of Rb-82m solution for future clinical PET applications. In this study, following production and formulation of Rb-82m as a PET radiopharmaceutical, the preliminary imaging studies was acquired by a dual head SPECT system, equipped with a co-incidence camera. Also, due to the production of 81Rb/81mKr generator for country use in our institution, biodistribution of radiorubidium was studied in normal rats using Rb-81 radioisotope. Production of rubidium-82m for imaging studies: Gasseous Krypton-82 with 30% enrichment and 251 mm thickness was irradiated under a pressure of 2.7 bar at 15.4 MeV energy in a stainless steel chamber. The target was cooled using 18 deg. C water while a current of 10 μA with a total current of 5.5 μAh was employed (maximum chamber pressure 3.6 bars). Details of the production system are summarized. After irradiation, the walls were rinsed with milli-Q sterile hot water in order to yield rubidium-82m in hydroxide form with an activity of about 35.0 ± 2 mCi (production yield: 6.37 mCi/μAh). The bombardment was performed with a proton current of 10 μA and a total proton dose of 5.5 μAh. After washing the compartment and extraction of 82Rbm, the activity of the final product was 35.04 mCi. Quality controls- Radionuclide purity: The gamma spectroscopy of the final sample was carried out by a HPGe detector. Biodistribution studies. The distribution of [82mRb]Rb among tissues was determined in rats. A volume (0.1 ml) of final [82mRb]Rb solution containing 20-40 μCi. Imaging studies. 0.1 ml volumes of the final [82mRb]Rb solution containing 300 μCi radioactivity (≤ 6 ng rubidium in 50 μL) were injected into the dorsal tail vein of healthy rats. As a result of the bombardment of 82Kr with 15 MeV protons, 35.04 mCi activity was finally achieved. The nuclear reaction efficiency was 6.37 mCi/μAh. Total production and formulation of [82mRb]Rb took about 60 min. TLC showed that the radiochemical purity of [82mRb]Rb was >95%. In contrast to other PET radiotracers for cardial studies, [82mRb]Rb has a rather long half life that causes long data acquisition times by PET or co-incidence systems. High chemical stability of the radiopharmaceutical, makes it easier for autoclaving process. Biodistribution studies performed by Rb-81 isotope was performed in normal rats