• A simple X-ray image can provide useful, but limited, information about internal structures in a 2D image
• When a more comprehensive image is needed, a computerised axial tomography (CAT or CT) scan is used
• The main features of the operation of a CT scan are as follows:
  • An X-ray tube rotates around the stationary patient
  • A CT scanner takes X-ray images of the same slice, at many different angles
  • This process is repeated, then images of successive slices are combined together
  • A computer pieces the images together to build a 3D image
  • This 3D image can be rotated and viewed from different angles

Advantages & Disadvantages of CAT Scans

• Advantages:
  • Produces much more detailed images
  • Can distinguish between tissues with similar attenuation coefficients
  • Produces a 3D image of the body by combining the images at each direction
• Disadvantages:
  • The patient receives a much higher dose than a normal X-ray
  • Possible side effects from the contrast media

Worked example

X-ray

The simple X-ray image involves taking a single exposure

This produces a single 2D image

CT scan

The CT scan requires taking several exposures of a slice from many different angles

This is then repeated for different slices before being combined together to build a 3D image

This involves taking a much greater exposure than the simple X-ray