Introduction to Nuclear Imaging

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Nuclear medicine is fundamentally an interdisciplinary branch of science. As opposed to traditional X-ray imaging, computer tomography (CT) or magnetic resonance imaging (MRI), nuclear medicine uses emission techniques. The basic principle of each method is the following: a radiopharmaceutical (a sort of isotope bound to a specific compound) appropriate for the particular purpose of examination is injected into the body of the person being examined, and the intensity distribution of the emergent radiation is measured with various devices. Examination equipments can be grouped into two classes depending on how the radiation emitted by the body is detected:

• detection of direct gamma-rays:
  • planar imaging (also known as scintigraphy). Results in a two-dimensional image.
  • SPECT – Single Photon Emission Tomography: taking both spatial and cross-sectional images is possible, a collimator must be used to form an image
• detection of gamma-rays emitted as a result of positron decay followed by annihilation:
  • PET - Positron Emission Tomography: the use of a collimator is not necessary, thus e.g. efficiency can be increased

 
Both dynamic (observing the changes in isotope distribution over time) and static examinations can be carried out. In most cases (i.e. static examinations) after the radiopharmaceutical has been injected in, one has to wait for the isotope distribution to reach a state of equilibrium, an image of which is then taken by some sort of nuclear medicine equipment.