Computed tomography is the ultimate development of X-ray technology. The principles are the same as those relating to film-based radiography, namely that an X-ray beam is modified as it passes through the body. The CT scanner collects digital information, and because of the way the X-ray tube and the detector move round the body of the patient, this information can be assembled into a 3-dimensional X-ray picture, allowing complete understanding of the nature of an injury or a disease process, such as a growing tumour.

Radiographs are good for distinguishing bone from soft tissues, as the beam is markedly modified by bone, compared to soft tissue. However, radiographs are not good at distinguishing different soft tissues, such as a tendon from skin, or a tendon from muscle, as the relative change in the beam between these different tissues is quite small. However, the computer software associated with a CT scanner allows artificial expansion of the grey scale, to magnify the difference between soft tissues, so that these can be seen on a screen as distinct structures. This is why CT scans can demonstrate soft tissue anatomy and disease processes in soft tissues, as well as changes in bones, in a way in which radiographs cannot.

A CT scanner used in a specialist veterinary practice