radiology This medical specialty originally involved the use of X-rays in the diagnosis and treatment of disease. Improved technology over the years with computer analysis of images has led to many sophisticated developments. Computed tomography (CT scans), developed by Sir Godfrey Hounsfield in 1972, was probably the most spectacular advance in radiology, using X-rays to provide three-dimensional information. Along with a progressive increase in the use of X-rays in diagnosis, other methods such as those utilizing gamma rays from radioactive isotopes (isotope scans), and positron emission tomography (PET scans), became incorporated into the modern practice of radiology. More recently radiologists have become involved also in ultrasound and magnetic resonance imaging (MRI) which do not involve ionizing radiation. Further sophistication has led to Doppler ultrasound, duplex scanning, and MRI angiography. These diagnostic methods are all known as organ imaging or imaging techniques and are described more fully elsewhere. They display in superb detail various organs or blood vessels and are very much a part of a modern radiologist's activities.

When one reflects that X-rays were only discovered in 1895, the developments have been quite staggering and expensive. Who could have foreseen, a hundred years ago, that putting patients inside magnets (MRI) could produce images? We are in the Golden Age of radiology with not enough gold to do all that is possible. Present day radiologists must be aware of the potential of these imaging methods, ensuring that optimal diagnostic pathways are followed. Radiologists now tend to subspecialize: neuroradiologists work solely within the nervous system, while others develop expertise in chest, bone, or gastrointestinal investigations.

Interventional radiology — dealing not with diagnosis but with treatment — is now a special field where various procedures are carried out using radiology for a visual display. Thus, under X-ray control, a catheter or needle may be positioned for various purposes; narrowed blood vessels in the leg or heart can be dilated (angioplasty); stents can be placed to widen arteries, bronchial airways, or ducts in the urinary or biliary tracts; tumours can be embolized (injected with material to block their blood vessels) to reduce their size; and abscesses can be drained.

J. K. Davidson

See also imaging techniques; magnetic resonance imaging; radioactivity; radiotherapy; X-rays.