Measurements of the rubidium isotopic activities and the elution parameters of 81mKr generators using a standardized 114mIn source

A method is described for measuring a number of parameters associated with an inorganic ion-exchange krypton generator. These are the activities of rubidium isotopes in inorganic ion-exchange krypton generators, the ^81mKr extraction rate, the ^81mKr activity delivered to patients during ventilation studies, the elution efficiency, and the radionuclide purity of the eluted gas. The method is based on the calibration of detectors, Ge(Li) and NaI(Tl), with a standardized ^114mIn source at matching photon energies. The average activities present in our generators at the end of bombardment (EOB) were 14.6±3.8 mCi (⁸¹Rb), 6.2±1.6 mCi (^82mRb) and 53±9.4 Ci (⁸³Rb). The ^81mKr extraction rate 2 h post-EOB was 10.2±2.3 mCi/min at an air flowrate of 1 l/min. The ^81mKr activity delivered to patients during a ventilation study was 91±16 mCi. The elution efficiency of the generators averaged 50%±7% at an air flowrate of 1 l/min. The eluted gas contained Rb radioisotopic impurities in trace quantities of approximately 0.06 Ci/l.