Computed tomography

From ArticleWorld

Computed tomography (CT) refers to the modern medical technology that makes use of X-ray imaging and computerized digital image processing to produce three-dimensional images of the internal parts of the human body. Since a series of images is taken about a single axis, this process is also referred to as ‘computed axial tomography’. Though the technology is primarily used in healthcare, it also finds important applications in the civil and mechanical engineering fields. Internal cracks, structural/foundational damages and deteriorated machine parts can be pinpointed using this technique. Commonly known as non-destructive testing (NDT) in engineering parlance, this technique does not require the dismantling of an object to be tested.

The technique

The word ‘tomography’ is derived from two Greek words ‘tomos’ meaning ‘slice’ and ‘graphia’ meaning ‘description’. Several axial views can be adjusted with the help of a technique called windowing. A particular image can thus be prepared in a different plane.

An X-ray source is used to prepare X-ray ‘slice’ images, with the X-ray sensors fitted on the side opposite to where the X-ray source has been installed. The several scans that are taken are combined using a special mathematical procedure called ‘tomographic reconstruction’. In most machines an X-ray tube is rotated behind a circular case. The patient going through a scan is made to rest on a movable table at the centre of the scanner. After views from several angles are taken, the various slices are combined to allow doctors to study three-dimensional images of the internal parts of the human body. There have been several advances in recent times with the result that the amount of radiation required has been reduced and the capacity to reconstruct the required images has improved considerably.

In order to improve the contrast between various internal body parts including blood vessels, special fluids may be injected into the body, or the patient may be asked to drink a contrast-enabling liquid.

History and development of computed tomography

The CT system of today was invented in 1972 by British engineer Sir Godfrey Newbold Houndsfield and American physicist Allan McLeod Cormack. The first CT machine took more than four minutes to finish scanning and almost a minute and a half to construct a three-dimensional image from the available data. Both the researchers, after several separate experiments, were soon recognised internationally and were awarded the Nobel Prize for medicine in 1979.

The first CTs were used to take images of the tissues in the brain. This continues to be the primary use till today, with the help of which brain disorders can be diagnosed. Apart from this, CT scans can help ascertain a range of other disorders such as those affecting the abdomen, chest, pelvis and spine. CT scans can be carried out on minute blood vessels as well, in a process known as angiography. CT scanning today is used to determine the exact size of tumours as also to examine narrow airways of the lungs.

Newer generation CT systems have seen the emergence of faster scanning and computing equipment. A new technique called the magnetic resonance imaging (MRI), using magnetically charged particles is becoming common nowadays. However, computed tomography continues to remain popular because of its several advantages including the low cost, superior imaging of the internal body parts and the ability to produce results without a need for a strong magnetic field.