ABSTRACT
Ionizing radiation is a powerful tool in many branches of medicine, as both an aid to diagnosis and a means of therapy (treatment). For diagnostic purposes there are two basic approaches. The first is to pass a beam of radiation, normally X-rays, through the body onto an image-capture device such as a semiconductor flat panel detector (FPD) built into the patient table. The different degrees of absorption in the body produce a picture that gives information on the structure of the internal organs. For example, conventional X-ray techniques can reveal broken bones, diseased lungs or the presence of a tumour. Another technique of great importance in medical diagnosis, based on the same principle, is computed tomography (CT), popularly known as scanning. A tomograph is an image of a section, i.e. a slice, through an object, in this case the human body. The second diagnostic approach is to introduce a radioactive tracer into the body, for example by mouth or by injection into the bloodstream, and to observe its behaviour by means of external detectors. This technique can give information on the location and development of disease and functioning of body systems, such as cerebral blood flow.
