24.3.1 Tracers

Tracers

Definition: Tracer

• A substance containing radioactive nuclei that can be introduced into the body and is then absorbed by the tissue being studied.

Types of Tracers

PET Scanning

For PET (Positron Emission Tomography) Scanning, the tracer used must be a ${\beta }^{+}$ emitter.

Fluorine-18

• Fluorine-18 is a radioactive nuclide which is a ${\beta }^{+}$ emitter.
• It decays via the following equation ${}_9^{18}\mathrm{F}{\to }_8^{18}\mathrm{O}{+}_1^0{\beta }^{+}{+}_0^0\nu$

Fluorine-18 Tracers

• Fluorine-18 can bind to glucose molecules forming fluorodeoxyglucose.
• The fluorodeoxyglucose has very similar chemical properties and structure to glucose, allowing it to be absorbed by the tissues to be studied during metabolic processes.
• Fluorine-18 has a short half life ($\approx 110\text{ minutes}$), which minimises the exposure of the patient to ionising gamma rays.

Usage of a Tracer

Usage of a Tracer

1. The tracer is introduced into the body via injection or ingestion.
2. The tracer travels through the body and is absorbed by specific tissues.
3. A radiation detector is used to track its progress.
4. Different radionuclides are used as the tracer depending on which substances are naturally absorbed by the tissue being studied.