Last revised by Sajanakan Sriselvakumar on 2 Aug 2023

Radiopharmaceuticals are drugs that are bound to radioactive substances. They may be used for diagnostic imaging, as therapeutic agents, or both (theranostic).

The most commonly used radionuclide is Technetium-99m. In some cases, such as Iodine-123, the radioactive molecule itself has a physiologic distribution that allows it to image the target organ. In others, the radioactive portion of the molecule is used primarily to tag and provide an imaging method for the pharmaceutically-active portion, which changes the biological distribution. One example of this is I-123 MIBG.

The particles emitted from diagnostic radiopharmaceuticals are detected either directly or indirectly by specialized equipment (e.g. SPECT, PET, gamma camera, etc.) to generate imaging. In other cases, the agent is used to have a tissue effect locally. For example, the alpha-emitter Ra-223 dichloride is used as a treatment for symptomatic osseous metastases and is not typically imaged.

The radioactivity of radiopharmaceuticals are commonly measured by using miliCurie (mCi) and megaBecquerel (MBq) where 1mCi is equivalent to 37MBq 1.

Properties of an ideal diagnostic radiopharmaceutical

  • short physical half life time

  • eliminated from the body with an effective half life time approximately equaling the examination time to prevent subsequent exposure to the body

  • pure gamma emitter by isomeric transition

  • gamma rays emitted should be monoenergetic (~150KeV)

  • high specific activity

  • localize largely and quickly at the target site

  • decay into a more stable daughter nucleus

  • easily and effectively attached to the chemical compound at room temperature

  • low cost per patient dose

  • can be easily produced or stored at the hospital site

ADVERTISEMENT: Supporters see fewer/no ads