• When a section, or slice, is taken through the body, it is divided up into a series of small units called voxels
• The image of each voxel has a particular intensity, known as a pixel
• The pixels are built up from the measurements of X-ray intensity from several different directions around the section of the body being studied

Building up an Image

• Take a section made up of 4 voxels
• Each voxel in the section has a particular intensity
  • The lower the intensity, the more X-rays are absorbed
• X-rays are directed at the sample from one direction
• The detector measures the sum of the intensities in the row of voxels that the X-rays were directed through
• The process is then repeated from several different directions
• Once this data has been collected, the ‘background’ intensity must be deducted
  • The ‘background’ intensity is the total of each set of detector readings
• After deduction, the result must be divided by the number of views of the section minus one
  • This corrects for the extra directions of the section that were viewed