critical organ

crit·i·cal or·gan

the organ or physiologic system that for a given source of radiation would first reach its legally defined maximum permissible radiation exposure as the dose of radiation is increased; for example, the kidney is the critical organ, receiving the most radiation, when Tc-99m dimethylsuccinic acid is given.

crit·i·cal or·gan

(krit'i-kăl ōr'găn) The organ or physiologic system that for a given source of radiation would first reach its legally defined maximum permissible radiation exposure as the dose of radiopharmaceutical is increased.