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Computed tomography

Synonyms: computed tomography, computerized tomography, CT scan, CT
German: Computertomographie

1 Definition

Computed tomography, in short CT, is an X-ray method with which the human body is represented in cross-sectional images (sectional imaging technique).

In comparison to the traditional X-ray image, where you can see only coarse structures and bones, a CT scan also captures soft tissues with little contrast difference in detail. CT scans can be viewed in 2D, or lately also in 3D with the aid of computer calculations.

2 Principle

In contrast to a conventional X-ray image, in CT, the patient is not only penetrated by radiation from one side, but he is completely scanned from all directions by a rotating X-ray tube while being moved forward through a round opening of the computer tomograph.

Further technical details see: Computer tomograph

3 History

3.1 Discovery

CT was developed in 1972 by the American physicist Allan M. Cormack and the British engineer Godfrey N. Hounsfield. For this, they obtained the Nobel Prize for medicine in 1979.

CT is regarded as the greatest invention in radiology since the discovery of the X-rays (by Wilhelm Conrad Röntgen in 1895). CT belongs to the most important imaging techniques in the diagnostics of tumors, bone fractures, inflammations etc.

3.2 Milestones in the development of the CT

Within a very short time, CT was established as one of the most important imaging techniques in medicine. Since its introduction, the CT scanner and software have undergone a rapid development.

  • 1972 first CT scanner
  • 1974 first commercial CT system with instant image reconstruction (tube rotates 360° around the patient, then still with fixed table position)
  • 1987 spiral CT: further technical development, "volume recording technique", the patient is continuously moved on the table through the measuring field, while the tube is rotating by 360° several times, so the patient is scanned in a spiral form
  • 1994 sub-seconds spiral CT: improved resolution, thinner slices, larger volumes are captured faster, the patient needs to hold his breath for a shorter time
  • 1996 Ultra Fast Ceramic detectors: reduced radiation dose, same image quality
  • 1998 multisclice spiral CT: 4 slices per rotation, rotation time only 0.5 seconds; cardio CT is made possible
  • 2005 dual source CT: instead of only one X-ray unit and one detector as of then, from this point on two of each in one gantry

Especially the image quality and recording time improved. While the first-generation devices took several minutes for a tomography scan, the current scanners only take fractions of a section.

3.3 Prospects

In June 2012, a new technique was presented to the European Synchrotron Radiation Facility (ESRF) in Grenoble with the sliding-window-technique. This technique considers also another reciprocal effect next to the absoprtion of X-rays in the tissue, the so-called grid interferometry. With this, you can reach a significantly higher contrast under much less radiation exposure in CT. Researchers hope to be able to apply the technique in clinical practice soon.

4 Usage

CT application is versatile and it has become indispensable in clinical routine. The numerous possible applications include:

4.1 Contrast medium

For better delimitation from certain structures (vessels, intestines etc.), for many exams, you need to inject a iodine-containing contrast medium into the vein at the beginning of the examination.

5 Variants

By digital post-processing of the voxel data, you get new possibilities. So, you can visualize vessels in 3D with CT angiography (CTA) (vascular representation for the detection of narrow sections). With the perfusion CT, you can calculate how much a certain tissue is supplied with blood (stroke and tumor diagnostics). With cardio CT, you can visualize calcified coronary vessels. The high-resolution computed tomography (HRCT) is an important technique for the diagnostics of pulmonary diseases.

6 Risks and benefits, complications

  • Advantages: good resolution, short examination time, non-invasive, by now available in almost every hospital
  • Disadvantage: relatively high exposure to radiation
  • Complications are only to be expected in association with the application of the contrast medium, which can lead to allergic reactions in some persons. In case of renal dysfunction, hyperthyroidism and allergies, you need to be careful. Truly life-threatening complications are absolutely rare.

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