The word "Radioactivity" is often used in two ways. It is used to describe the phenomenon of Radioactivity - that is the decay of unstable nuclei with the consequent emission of radiation, but it is also used in a quantitative sense - that is the amount of radioactivity present. This can be defined as "the number of nuclear disintegrations per unit time in a given amount of the preparation". Radioactivity concentration would therefore normally be expressed in terms of Radioactivity per unit volume, for example MBq per ml.
Radioactivity is important in radiopharmacy since most doses are measured in radioactive units rather than units of mass. The dose administered determines:
· the radiation dose received by the patient
· the diagnostic quality of any imaging procedure, and
· the efficacy of any therapeutic administration.