Introduction to radionuclide imaging

Radionuclide imaging involves the introduction of a radioactive source into the patient. This is done with radiopharmaceuticals which consist of a radionuclide that emits gamma radiation and a pharmaceutical part which is the physical/chemical component to which the radionuclide is attached to. It is the pharmaceutical that largely determines the physiological behaviour of the radiopharmaceutical and, therefore, the nature of the image obtained.

Radionuclide imaging differs from projection radiography (plain films and CT) in several ways:

Projection radiography Radionuclide radiography
X-ray photons used to form images Gamma radiation used to form images
X-rays projected through patient from an outside source Radioactive substance introduced into patient and image formed by radioactivity leaving patient
Image contrast created by physical properties of the imaged object i.e. density and average atomic number Image created by differential uptake of the radioactive substance by the organs
Radiation dose determined by settings of x-ray tube (e.g. mAs and kV) and scatter. The longer the scan the higher the dose Radiation dose determined by type and quantity of radiopharmaceutical introduced into patient. The length of the scan does not affect dose
Image created with x-ray photon detectors Image created using a gamma camera


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