A Rb-81/Kr-81m generator for liquid elution

Rb-81/Kr-81m generators for liquid elution are not commercially available in South Africa. None of the generators described in the literature can be copied in exactly the same form, because of the composition of the locally available Rb-81 solution. Thus a generator capable of delivering a Kr-81m solution suitable for intravenous infusion had to be developed for use at Tygerberg Hospital. The existing ion exchange column type Rb-81/Kr-81m generator for ventilation studies was used as starting point. Modifications in the construction and preparation enabled elution of a sterile, pyrogen free product for continuous infusion. Experiments with different column sizes showed that the high concentration of sodium in the locally available Rb solution necessitates much larger ion exchange columns to bind Rb-81. The very short half lives of both the mother and daughter nuclide prevent complete quality testing of the product before use. Analyses of eluates of prototype generators have shown that the eluates were acceptable as far as sterility, apyrogenicity, pH and chemical purity are concerned but that they contained the radionuclide impurities Rb-81, Rb-82m, Rb-84 and Na-22 while the presence of Rb-83, Na-24 and Br-82 could not be excluded. It was shown that levels of contamination were relatively high compared with those reported in literature. Use of an additional smaller column in the system to serve as a Rb-trap removed the impurities almost completely and is strongly recommended to reduce radiation dosages to patients. A method was developed to compare the yield obtained from different generators and used to study the influence of different factors on Kr-81m yield. From the results the optimal generator was chosen. A Rb-81/Kr-81m generator providing Kr-81m in a 5% dextrose solution suitable for intravenous infusion can now be assembled at Tygerberg Hospital