Medical Tracers (OCR A Level Physics)

Medical Tracers

• A radioactive tracer is defined as:

  A radioactive substance that can be absorbed by tissue in order to study the structure and function of organs in the body

• Radioactive isotopes, such as technetium-99m or fluorine-18, are suitable for this purpose because:

  • They both bind to organic molecules, such as glucose or water, which are readily available in the body

  • They both emit gamma (γ) radiation and decay into stable isotopes

  • Technetium-99m has a short half-life of 6 hours (it is a short-lived form of Technetium-99)

  • Fluorine-18 has an even shorter half-life of 110 minutes, so the patient is exposed to radiation for a shorter time

• A common tracer used in PET scanning is a glucose molecule with radioactive fluorine attached called fluorodeoxyglucose

  • The fluorine nuclei undergoes β⁺ decay – emitting a positron (β⁺ particle)

• The radioactive tracer is injected or swallowed into the patient and flows around the body

• Once the tissues and organs have absorbed the tracer, then they appear on the screen as a bright area for a diagnosis

  • This allows doctors to determine the progress of a disease and how effective any treatments have been

• Tracers are used not only for the diagnosis of cancer but also for the heart and detecting areas of decreased blood flow and brain injuries, including Alzheimer's and dementia