CT, computer tomography, tomography, tomography of layers, tube examination, CT scanning English: cat – scan
Definition
Computer tomography is ultimately the further development of X-ray examination. In computed tomography, X-ray images are taken from different directions and converted into tomograms by means of the computer. The name computed tomography is derived from the Greek words tomós (cut) and gráphein (write).
The method of computer tomography was developed in 1972 by the American physicist A. M. Cormack and the British engineer G. N. Hounsfield. The two researchers were awarded the Nobel Prize for Medicine in 1979 for their achievements. In CT examination/computed tomography, a beam of X-rays is generated using a classical X-ray tube and a narrow beam of X-rays (fan beam).
X-rays are absorbed to different degrees by different types of tissue. Strongly absorbing layers are especially bone tissue. The detectors on the opposite side of the CT ́s detect the transmitted X-ray radiation.
The X-ray tube of computed tomography rotates perpendicularly to the patient’s body axis and thus bypasses the entire patient and continuously emits and detects the transmitted X-ray radiation. The detectors produce electrical pulses in response to the X-rays. The computer now calculates an image in different shades of grey from the individual impulses collected during the bypass of the patient.
If this process is repeated layer by layer, the individual slice images are created. In modern computer tomographs, several slices can be run simultaneously. Generally, section thicknesses between 1 mm – 1 cm are selected.
Compared to the X-ray image, there are no overlapping effects in computed tomography examinations. All points in computed tomography can be clearly assigned three-dimensionally. Therefore, sizes can be clearly determined and structures can be clearly assigned.
Due to the possibility of digital post-processing, three-dimensional images of bones and ligaments can be created. In special cases, e.g. in tumor diagnostics, the informative value can be increased by the administration of contrast medium through stronger contrasting. Computer tomography is ideally suited for the imaging of bone tissue.
It is therefore used in many areas of medicine. Important areas of application are:
- Computer tomography of the head (CCT, cranial computer tomography): It is used in cases of suspected bleeding, brain tumours, age-related changes, stroke (apoplexy/apolplex) and bony skull injuries. – Whole-body CT:A whole-body CT is particularly used in the search for tumour metastases or seriously injured people in order to obtain as much information as possible. – Skeletal computer tomography:This is the most common examination technique used in orthopaedics. Special indications are:Herniated disc (rare indication when an MRI cannot be performed)Osteoporosis (also for determining bone density as qCT)Bone fractures (fractures)
- Herniated disc (rare indication when an MRI cannot be performed)
- Osteoporosis (also for determination of bone density as qCT)
- Bone fractures (fractures)
- Herniated disc (rare indication when an MRI cannot be performed)
- Osteoporosis (also for determination of bone density as qCT)
- Bone fractures (fractures)
All articles in this series: