ABSTRACT
The radiation is delivered to subject bodies by the administration of a small amount of tracer that is labeled with radionuclides. A tracer labeled with a radionuclide is called a radiopharmaceutical. The radiation is created when radiopharmaceutical decays and produces either directly or indirectly photons that are later detected by the NI camera. In certain radioactive decay, photons (at least one) are the direct product of the nuclear reaction that occurred. In an indirect photon production, the radioactive decay produces a positron (positively charged electron) which annihilates producing a couple of secondary photons. Because the principle of detection of the direct and indirect photons is different, two imaging modalities are identified. The single photon emission modality that includes planar and tomographic (single photon emission computed tomography or SPECT) scans is concerned with imaging using direct photons and Positron Emission Tomography (PET) concerned with imaging positrons (or indirect photons). In Sections 5.3.3.1, 5.3.3.2 and 5.3.4.1 we provide details that differentiate those nuclear imaging modalities.
