Computed Tomography Scanning (Cambridge (CIE) A Level Physics): Revision Note

Computed tomography scanning

• 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

CAT scan diagram

CAT scans take 2D images from multiple positions to create a 3D image

Advantages & Disadvantages of CAT Scans

• Advantages of CAT scanners:

  • They produce images of much higher resolution (compared to a single X-ray image)

  • They can distinguish between tissues with similar attenuation coefficients

  • They produce a 3D image of the body by combining the images taken in each direction

• Disadvantages of CAT scanners:

  • The patient receives a much higher radiation dose than a normal X-ray

  • There are possible side effects from the contrast media