[A fundamental study of 99mTc-ethyl cysteinate dimer (99mTc-ECD)]

In vitro fundamental studies of 99mTc-ethyl cysteinate dimer (99mTc-ECD), a newly developed radiopharmaceutical for cerebral perfusion scintigraphy, were performed, and were compared with those of 99mTc-HM-PAO, which has been widely applied to clinical use. 99mTc-HM-PAO should not only be injected soon after reconstitution, but also be avoided mixture with saline or drugs such as Diamox, because of its radiochemical purity decreases with the passage of time and the addition of saline and Diamox. On the other hand, the radiochemical purity of 99mTc-ECD reached a constant level of 94-96% at 30 to 180 min after reconstitution, and it remained stable against the addition of saline and Diamox. Therefore, it was suggested that 99mTc-ECD could be injected from an already saline-infused venous-line or mixed with Diamox. However, early injection after reconstitution should be avoided, because 99mTc-ECD did not become stable enough to maintain sufficient radiochemical purity until 30 min after reconstitution. The present studies are suggested that the red blood cell component is largely related to the metabolism of 99mTc-ECD in blood. Furthermore, from study of the metabolic rate using rabbit blood, it was suggested that a species difference existed in esterase activity in blood.