Computed tomography (CT)

The development of computed tomography (CT)

Computed tomography (CT) makes it possible to produce three-dimensional images of the body using X-rays. The mathematical basis of computed tomography was first outlined by Austrian mathematicians Johann Radon. A mathematical process known as the Radon transformation provides the basis that allows the computation of a spatial record of any object. In 1957 and 1963, Allan M. Cormack developed algorithms to calculate the absorption of X-rays by human tissues. The first prototype of a CT device was developed by Godfrey Hounsfield in 1969. The first CT procedures on human beings were made in 1971. The first commercial computed tomography devices came on the market from 1972 for use in radiological diagnostics. Since then, CT technology has been developed progressively. One milestone in this development process was the introduction of the helical CT by German physicist Willi A. Kalender. The first multi-slice CT was launched on the market in 1992. Over the years to follow, the number of slices increased to 320 detector slices. What this means is that each X-ray rotation produced the data necessary for 320 cross sectional slices simultaneously, or even 640 such images where a double reading process was used. In 2005 the first CT scan using two X-ray tubes (dual-source CT) was launched.  This allowed the use of two X-ray tubes positioned at 90° from one another.

Modern multi-slice computed tomography devices scan a large number of anatomical slices simultaneously at a slice thickness of less than 1 mm. During the CT examination, the patient is progressively moved along a table through the CT device as the X-ray tube rotates around him or her. This provides the data needed to create an anatomical representation achieving a maximum resolution of 0.25 mm isotrope Voxel (i.e. a measure spatial resolution that is equal over each of the three dimensions). The data is then used to reconstruct images showing cross sections taken across any plane.

Diagnostics in human medicine

Computed tomography has become established as the most important diagnostic procedure in radiology. Bone fractures, bleeding, injuries to organs, inflammations and tumours can all be detected safely using computed tomography. The same applies to slipped discs and to degenerative changes in bone structure and substance in the spine and joints.

As compared to magnetic resonance imaging (MRI), the time required for CT scan examinations is very short. This aspect of the procedure makes it suitable for use in scans of larger areas of the body in a single session. For scans of the neck, ribcage and abdomen at the same time, for example. Care should always be taken, however, that the volume of the body chosen for examination is as small as possible, and that the radiation dose is kept to a minimum in order to achieve the best possible radiation hygiene. The use of this examination strategy has proven itself in particular in the diagnosis of tumours and in searching for metastases. In addition, computed tomography also facilitates the early diagnosis of ailments of lung tissues.