Technetium-99m radiopharmaceuticals account for nearly 80% of diagnostic studies in nuclear medicine. These agents are available for imaging almost all the important organs of the body and are routinely used worldwide due to the favourable logistics of having a transportable 99Mo–99mTc generator in the hospital radiopharmacy.

Technetium-99m radiopharmaceuticals were introduced in the mid-1960s, when static cameras were the standard nuclear medicine imaging equipment and other imaging modalities such as magnetic resonance imaging, computed tomography or ultrasound were not available. Introduction of these competing imaging modalities has influenced nuclear medicine to focus more on dynamic and functional studies. Functional imaging involving in vivo biochemistry is unique to nuclear medicine, and its clinical usefulness has been established using positron emission tomography (PET) together with small bioactive molecules labelled with positron emitting radionuclides.