Medical Physics

  • Created by: roopa
  • Created on: 11-04-15 14:24

The Gamma Camera


The gamma Camera is displayed to the left, you need to be familar with how its key features.

  • Collimator Tubes - The gamma ray photons travel along the axis of these lead tubes. The quality of the image can be improved by having longer / thinner tubes.
  • Scintillator (NaI Crystal) - The gamma ray photon produces many visible light photons
  • Photomultiplied Tubes - Electrons are produced by the photons of light
  • Computer - The electrical signals are used to create an image.
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Positron Emission Tomography (PET)


PET scanners take advantage of the annihilation event between a positron and an electron. The key stages are:

  • A patient is injected with a positron emitter.
  • An annihilation event between a positron and an electron takes place producing two gamma ray photons
  • These gamma ray photons travel is opposite directions
  • The patient is surrounded by a ring of gamma detectors. The arrival times of the photons are used to pinpoint areas of increased brain activity.
  • A 3D image is made by a computer making use of the detector signals.
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Computerised Axial Tomography (CAT) Scanner

( scans provide a way of creating a 3D image using X-rays. 

  • The x-ray tube rotates around the patient, allowing x-ray beams to pass through the patient at different angles. 
  • The shape of this beam is thin fan (see diagram)
  • With the help of a computer, images of slices of the patient are produced. 
  • By moving the x-ray tube we get an image of a different slice.

The fact that the images produced are in 3D is one advantage of CAT scans over a traditional X-ray. Another advantage is that there is better contrast between different soft tissue.

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