Computer tomography CT, magnetic resonance imaging and positron emission tomography explained

In this article we want to present the CT, MRI and PET imaging procedures in more detail. We hope to explain the difference between the various image types in an understandable way. Perhaps we can also show you when CT and MRI make sense and why the one or the other imaging technique is used.

Computer tomography (CT), magnet resonance imaging (MRI) and positron emission tomography (PET)

Computed tomography is usually performed to supplement sonography. This is an X-ray examination in which a contrasting substance is administered intravenously. The part of the body to be examined is X-rayed layer by layer so that the location and size of the tumour can be determined precisely. Any existing metastases in the liver, lungs or lymph nodes can also be detected in the CT.
Magnetic resonance imaging is performed as an alternative to computer tomography, in some cases also as a supplement. MRI is not an X-ray examination, but is based on magnetic field effects. The results of MRI and CT examinations are comparable in terms of tumour stage and operability. (Source: TEB Compass)

Both imaging methods utilize different techniques (echo principle - X-ray examination). Both complement each other, but are not mutually exclusive procedures. They are each of value but are used differently.
Often the US (ultrasound examination) alone is not sufficient and questions remain concerning the optimal assessment of individual structures and disturbing factors.

Further imaging procedures such as CT and MRI are included in the treatment and can usually clarify these open questions.

Computer tomography (CT)

In order to be able to perform a CT, the affected person is pushed through a scanning tunnel (scanner). X-rays are used to create cross-sectional images of the body in slices and then assembled by a computer in order to obtain a three-dimensional representation of the organs. This imaging procedure is very often used in diagnosis, but also to compare the course of treatment and therapy. The radiation exposure is higher than with classical x-rays.


Magnetic Resonance Imaging (MRI)

MRI is ideally suited to identifying cystic tumours. MRI or magnetic resonance imaging works with a magnetic field. Here the affected person is also pushed into a ring-shaped scanner, as in the CT, in order to take some pictures of the inside of the body in layers. Duration of the examination approx. 15 - 45 minutes. With this procedure, the organs can be very well represented. Recently MRI has also been improved: For example, patients no longer always have to lie in a scanner that surrounds the entire body, which is perceived as much more pleasant. Affected people find anxiety or the feeling of confinement in a scanner very disturbing. Administering a mild sedative can often help here. In contrast to CT, MRI does not expose the body to radiation, which many patients consider an advantage and relieves them of their fear of additional radiation exposure. The imaging procedure to be used in each individual case should always be discussed with the doctor in charge.


Positron emission tomography (PET)

PET is mainly used for recurrent tumours and is also a scanner in which the affected person lies. Before the PET is used, the patient must be injected with a weak radioactive substance, which distributes itself in the body and is then captured with the help of a special camera.
Different substances are used in different parts of the body. The radioactive rays of this procedure pollute the body only for a short time, but the administered substances disintegrate within a few hours and therefore the procedure is well tolerated.


Images and associated text sources: Prof. Dr. Götz M. Richter

No. 1 shows a relatively small pancreas carcinoma of the tail in the MRI and is recognisable by the dark zone, which can be clearly seen against the contrasting healthy pancreas tissue.

No. 2 shows the clear retention of fluid in the pancreatic duct caused by the tumour itself, and which is recognisable as the white curving structure of the pancreatic tail.

No. 3 shows a so-called Hydro-CT, when the patient drinks so much water before the examination, so that the pancreatic tumour can be especially clearly diagnosed. This picture is taken of the post-contrast-phase, easily recognised by the very light aorta. And directly on the right next to the aorta you can recognise the tumour because it absorbs much less contrast medium than the pancreas itself.

No. 4 shows the same examination as in No. 3, but in the venous KM-stage. Here again the tumour on the aorta is well recognisable because it absorbed much less contrast medium.

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