Comparison of different techniques may be carried out using standard radiation dose indices measured in perspex phantoms, with the CTDI value being the most widely used value. These values are referred to in defining Reference Dose Levels for different CT scans. These require careful calibration and handling, and can be time-consuming to use. These are used as reference values, adjusted to take account of the particular scanning parameters and scan coverage used for the patient in question. These estimates rely on the scanner in question matching the radiation dose characteristics of a scanner in the reference database.
ImPACT produce data to give advice on which scanner data sets to use in a particular case.
Computer software has been written to enable these calculations to be rapidly carried out. When making the choice of a CT system, the potential purchaser is often confused by conflicting claims as to the superiority of different design features. Scanner generation - 3rd and 4th generation designs and their effects on scatter discrimination, spatial resolution, and ring artefacts. In each case a description will be given of the design feature, conflicting claims discussed and examples given of scanner models with a given design. The conclusion is reached that different designs have their inherent advantages and disadvantages but many of the latter can be overcome.