PET scanning

Explain what is meant by a medical tracer

• A radioactive substance is injected into the patient;

• which is then absorbed by the organ/tissue.

Give an example of a medical tracer that is commonly used to diagnose the function of organs

• Technetium-99m;

• lodine-131;

• Fluorine-18;

• NOT Barium.

Name and describe the function of the main components of a gamma camera

• The collimator/lead tubes - only gamma photons that travel along the axis of the lead tubes pass through the collimator and are detected;

• Scintillator / sodium iodide crystal - the incident gamma ray photon produces many photons of visible light;

• Photomultiplier tubes / photocathode and dynodes - electrons are produced by each photon of visible light, producing an electrical pulse;

• Computer - the electrical pulse from the photomultiplier tubes are used to generate an image.

State how the quality of the image produced by a gamma camera can be improved

• The quality of the image is improved by using narrower or longer collimators, or a longer or a longer scanning time.

Explain the basic principles of PET scanning, including how the image is formed

• The brain/body is surrounded by a ring of gamma cameras/detectors;

• The positrons from the F-18 nuclei annihilate electrons inside the patient;

• The annihilation of a positron and an electron produces two identical gamma photons, which travel in opposite directions;

• The delay time between the detection of these two photons in the gamma cameras is used to determine the location of the annihilation (which are areas of increased activity);

• A computer is connected to the gamma cameras/detectors and an image is formed by the computer using the electrical signals from the detectors.