Magnetic resonance imaging or magnetic resonance imaging works on the principle of magnetism.
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In contrast to computer tomography, magnetic resonance imaging does not work with X-rays, but with magnetic fields and radio waves.
As the functioning of an MRI is very complex, only the basic operating principles will be briefly explained here without going into physical details.
The human body consists to a large extent of hydrogen atoms, which have a certain orientation similar to a compass. Under normal circumstances, the hydrogen atoms in the body are completely disorganised.
The strong magnetic field generated in the MRI scanner is able to orientate the atoms in a specific direction (similar to a compass needle, which can be moved in any direction by a magnet). This forced alignment of the hydrogen atoms means that they are now under a certain amount of tension. Using radio waves, which can be briefly generated by the tomograph, the atoms are then briefly deflected from their forced position. After the radio frequency pulse is switched off, the hydrogen atoms return to their original position and emit a signal that can be detected by an antenna.
High-performance computers are used to create a cross-sectional image of the examined body region from the signal.
The indications for MRI are very diverse.
The main focus of MRI is the visualisation of soft tissue structures, i.e. primarily non-bony structures such as organs, cartilage, tendons, muscles, brain parenchyma, intestines and vessels.
Tissue structures with a low water content, such as bones or air-rich regions (such as the lungs), can generally only be visualised to a limited extent. In principle, however, any region of the body can be examined using MRI.
Some further examinations are, for example
- Vascular imaging (MR angio, MR perfusion), Further information
- MR enterography (visualisation of the intestine)
- MRI of the heart (cardio-MRI), Further information
- Specialised contrast agent examinations of the liver (Primovist®)
- Functional magnetic resonance imaging
- Prenatal MRI diagnostics
- MRI of the breast / prostate
- MRI examination under anaesthesia (in cooperation with the Clinic for Anaesthesiology)
All metal objects must be removed before the examination, as they could otherwise enter the very strong magnetic field of the MRI scanner. Furthermore, electronic devices, wristwatches, credit or chip cards must not be placed near the device, as this could render them unusable or delete them.
If you have a pacemaker, artificial heart valves or other metallic implants implanted in your body, please be sure to let us know before the examination, as in this case the MRI scan may only be possible after special preparation or, in individual cases, not at all.
If you are claustrophobic, please also let us know before the examination, as you will have to lie still in a tube up to 1 metre long during the examination. If necessary, we can give you a sedative before the examination.
In some MRI examinations, contrast medium is used, which is injected via a peripheral vein. The following questions should be clarified in advance of such examinations:
Is kidney function normal?
As most of the contrast medium is excreted via the kidneys, a current blood value (creatinine, GFR) should be available. If necessary, kidney function must be supported by means of a fluid infusion before the examination.
Is there a known allergy to MRI contrast media?
An allergic reaction to MRI contrast media is very rare. If allergic reactions are known, anti-allergic medication must be administered in advance.
You should therefore inform us of any known pre-existing conditions before the examination so that we can make appropriate preparations if necessary.
In most cases, it is not necessary to be fasting for the examination. Fasting is only necessary if you are allergic to contrast media, for an MRCP or MR enterography, or if you are expressly advised to do so.
As with computer tomography, you will lie on a couch in the device during the examination. You should lie very still and breathe evenly.
As there is loud knocking noise from the machine while the images are being taken, we will provide you with headphones for noise protection. You will also be given a bell for the examination, which you can use to make yourself heard at any time.
For some questions, it is necessary to apply a contrast agent via a peripheral vein, similar to CT. These are not iodinated, but contain paramagnetic substances and are generally well tolerated.
The examination takes between 20 and 45 minutes, depending on the body region and the question being asked.
