Benefits and risks should be explained before testing. Patients retain the radioisotope for a relatively short period. The radioactivity decays over time. Some of the radioisotope is eliminated in urine, feces, and other body fluids.

^99mTc, the most commonly used radiopharmaceutical, has a radioactive half-life of 6 hours. This means that half of the dose decays in 6 hours. Other radioisotopes, such as iodine, indium, thallium, and gallium, take 13 hours to 8 days for half of the dose to decay.

1. Benefits:

   1. Nuclear medicine yields functional data that is not provided by other modalities.

   2. Nuclear imaging is relatively safe, painless, and noninvasive (except for IV administration).

2. Risks:

   1. Radiation exposure (minimal)

   2. Hematoma at IV injection site

   3. Reactions to the radiopharmaceutical (hives, rash, itching, constriction of throat, dyspnea, bronchospasm, anaphylaxis [rare])