In vivo comparison of 16 alpha[77Br]bromoestradiol-17 beta and 16 alpha-[125I]iodoestradiol-17 beta.

An in vivo comparison of two estrogen-receptor-binding radiopharmaceuticals of high specific activity, 16 alpha-[77Br]bromoestradiol-17 beta and 16 alpha-[125I]iodoestradiol-17 beta, has been carried out in immature female rats. The iodoestradiol has slightly higher uterine uptake at 1 hr after injection, whereas the brominated analog has significantly enhanced uptake at later times. The similar behavior of the two compounds in vivo suggests that estradiol labeled with I-123, Br-77, or Br-75 could be used interchangeably for the imaging of breast tumors containing estrogen receptors. In addition, coinjection of 16 alpha-[125I]iodoestradiol as an internal standard has been shown to be useful for comparison of different radiohalogenated estrogens.