Medical Applications of Radioactivity: Diagnostic Imaging and Radiation

"nuclear radiation depends on the nuclide and not on the chemical compound it is in, so that a radioactive nuclide can be put into a compound designed for specific purposes. When that is done, the compound is said to be tagged. A tagged compound used for medical purposes is called a radiopharmaceutical." "When the emitted positron β+ encounters an electron, mutual annihilation occurs, producing two γ rays. Those γ rays have identical 0.511 MeV energies... and they move directly away from each other, allowing detectors to determine their point of origin accurately." "The ratio of abnormal cells killed to normal cells killed is called the therapeutic ratio, and all radiotherapy techniques are designed to enhance that ratio." "we define a radiation dose unit called the rad. It 1/100 of a joule of ionizing energy deposited per kilogram of tissue, which is 1 rad = 0.01 J/kg." "the roentgen equivalent man is defined to be the dose in rads multiplied by the relative biological effectiveness. rem = rad × RBE"