Computed Tomography
Computed tomography (CT, sometimes incorrectly referred to as computer tomography) is an imaging method that uses X-rays to produce a series of cross-sectional images of the entire body. The resulting image is created through mathematical reconstruction of a series of X-ray projections obtained sequentially from various angles. Computed tomography also visualises soft tissues, such as the spleen, pancreas, kidneys, brain, and muscles. CT can be used to diagnose only those pathological processes that differ in density from the surrounding tissue during a plain scan or after the administration of a contrast agent.
Implementation[edit | edit source]
Using computed tomography, the cross-sectional images of a supine patient is acquired. The patient is secured to a sliding table that moves gradually through the scanning gantry. On one side of the gantry is a slit-type X-ray source (X-ray tube), and on the opposite side is an array of scintillation detectors. In some CT scanners, the detectors are positioned opposite the X-ray tube and move in sync with it. In the most modern CT scanners, the detectors form a complete ring around the patient that does not move.
The patient is scanned in a specific plane, point by point. The X-ray tube operates in pulses, with each pulse lasting 1–4 ms. X-rays pass through the patient, where they are partially absorbed. An exposure is taken at the patient’s current position, and data on the degree of X-ray attenuation obtained using scintillation detectors are recorded in the computer’s memory. The X-ray tube and scintillation detector system then rotates by a certain angle, and the entire process is repeated. After all patient scanning cycles are complete, all data from each scintillation detector are stored in the computer’s memory. This data is processed by the computer, and the resulting tomogram is determined by the absorption coefficients from individual tissue locations within the given slice.
CT scanners operate on two design principles: a fan-shaped or a circular design. In a fan-shaped scanner, both the X-ray tube and the detector array rotate, whereas in a circular scanner, only the X-ray tube rotates and the detectors are arranged around the entire circumference of the scanner.
From the perspective of technical development, CT is typically described in terms of five generations:
1st generation
X-rays were collimated into a narrow beam and, after passing through the patient, detected by a single detector on the opposite side that rotated along with the X-ray tube.
2nd generation
X-rays from the X-ray tube are collimated into a fan shape and, after passing through the patient, are detected by a larger number of detectors arranged in a single row on a circular segment opposite the X-ray tube, rotating along with the X-ray tube, this greatly accelerated the examination.
3rd generation
X-rays from the X-ray tube are collimated into a wider fan shape, similar to the 2nd generation, but the transmitted radiation is detected by a large number of detectors arranged in multiple rows along a circular arc, simultaneously capturing multiple slices ("multi-slice CT"). This is the most widely used method in modern medicine today.
4th generation
The detectors are arranged in a stationary configuration in a complete circle around the patient, with only the X-ray tube rotating
5th generation
Electron beam cardiotomography
History[edit | edit source]
German physicist Wilhelm Conrad Röntgen had a fundamental influence on the invention of CT; in 1895, he discovered X-rays, which are still used today to produce X-ray images. The British scientist Godfrey Newbold Hounsfield is considered the inventor of CT itself. Independently of him, the American physicist Allan McLeod Cormack made the same discovery in 1979, both were awarded the Nobel Prize. Previously, an examination took 20 minutes; today, it takes only a few seconds.
The Use of CT in Healthcare[edit | edit source]
In emergency medicine, there are no contraindications to the examination. CT scans are widely used for diagnostic purposes as well as for therapeutic procedures. Using X-rays, they produce images of internal organs and the skeleton. The resulting data from a CT scan can also be used as the basis for 3D models.
Benefits of CT[edit | edit source]
A major advantage of computed tomography is that it allows for the visualisation and differentiation of low-contrast soft tissues. This is primarily due to two reasons. Scintillation detectors, which capture X-rays that have passed through the patient’s body, are highly sensitive, and the data they provide is processed very quickly by a computer and expressed as absorption coefficient values, which greatly increases the accuracy of the examination.
A contrast agent is often administered before and during the CT scan to highlight the differences between normal and pathological tissue.
