Seven-hour stabilization of 99Tcm-exametazime (HMPAO) for cerebral perfusion

The objective of this study was to increase the stability of 99Tcm-exametazime and to investigate the effects of relaxing the eluate restrictions imposed by the manufacturer. We added 1800 MBq freshly eluted pertechnetate to 0.5 ml aliquots of stannous-enhanced exametazime followed by the addition of 0.7 mg gentisic acid and 0.5 ml sterile absolute alcohol BP. The radiochemical purity as measured by thin-layer chromatography was maintained at over 80% (range 88-99%, n = 40) for up to 7 h after preparation. High-performance liquid chromatography confirmed that the primary complex was maintained at over 80% (ranges 89-92%) for up to 7 h. In a second series of studies using the first eluate from a newly delivered generator to prepare 99Tcm-exametazime, a radiochemical purity of more than 80% was achieved for up to 7 h (range 88-95%, n = 24). In a third series using a 3-hour-old generator eluate, a radiochemical purity of more than 80% (range 88-93%, n = 18) was achieved for up to 5 h (for logistic reasons, we were unable to continue readings beyond 5 h). These results suggest that the manufacturer's restrictions on the eluate may be relaxed. Clinical validation was performed in a blinded study of 21 patients using single photon emission tomography. Image quality was assessed on the basis of salivary activity, nasal activity and the overall (global) image quality. There was no significant difference between the images obtained using the stabilized exametazime and exametazime prepared without gentisic acid and ethanol (chi 2 = 2.85, P = 0.05). We conclude that stabilization of 99Tcm-exametazime can be achieved for up to 7 h by using gentisic acid and alcohol and that the eluate restrictions may be disregarded.