The radiation dosimetry of 99Tcm-exametazime

The biodistribution of the regional cerebral perfusion imaging agent, 99Tcm-exametazime, has been studied with volunteer subjects at Aberdeen, Homburg, Manchester and Milan. Data from these studies have been pooled and analysed to formulate a kinetic biodistribution model, allowing estimation of time integrals of activity in various body organs. Estimates of radiation dose to humans injected with this material have been made by applying the MIRD formalism to these data. The highest doses occur to the lachrymal glands, gallbladder and kidneys (33, 27 and 18 mSv, respectively, per 500 MBq administered.) The lachrymal glands were visualized in only 6 of the 26 volunteer studies. The effective dose equivalent, for the worst case individual, is 8.3 mSv. In the majority of subjects where there was no uptake in the lachrymal gland, the effective dose equivalent reduces to 6.9 mSv.