Synonyms
Magnetic resonance imaging, magnetic resonance imaging, magnetic resonance imaging, magnetic resonance imaging
Definition MRT
Magnetic resonance imaging (MRI) is a diagnostic technique for imaging internal organs, tissues and joints using magnetic fields and radio waves. As a second step in magnetic resonance imaging, this stable alignment is changed by irradiating high-frequency electromagnetic energy in the form of a radio signal at a specific angle to the alignment of the hydrogen protons. The radio signal of the MRI causes the hydrogen protons to oscillate.
After the radio pulse has been switched off, the hydrogen protons return to their original position and release the energy they have absorbed through the radio pulse. In the third step, the emitted energy can be measured by receiving coils (principle of antennas). By means of a sophisticated arrangement of these receiving coils, it is possible to measure exactly in a three-dimensional coordinate system where when which energy has been emitted.
The measured information is then converted into image information by powerful computers. In magnetic resonance tomography (MRT), a complicated sequence of excitations and measurements (cf. magnetic resonance technology) serves as the basis for the creation of (sectional) images of the body’s interior.
With the help of computer processes, such as those already developed for X-rays, computed tomography and axial computed tomography, the measured signals are converted into image information. The behavior of hydrogen atoms depends on whether they are bound in liquids or solids, whether they move, e.g. in blood, or not. Due to the different content and presence of hydrogen atoms, healthy and diseased body tissue as well as healthy tissue can be distinguished from each other like no other medical procedure.
By changing the measurement conditions, the imaging of certain types of tissue, such as fatty tissue or cartilage, can be enhanced or suppressed. If the differentiation of tissues is not easily possible, well-tolerated contrast media are available, which allow further statements to be made about the body region under investigation. These contrast media do not contain iodine but are mostly based on gadolinium compounds (Gd-DTPA, gadolinium is a so-called rare earth).
Since only magnetic fields and radio waves are used in magnetic resonance imaging (MRI), there is no health risk to the patient according to current knowledge. Possible risks are posed by metallic foreign objects such as coins or keys that are drawn into the magnetic field and can cause injuries to the patient due to their acceleration. Therefore, all metallic objects must be handed in before the MRI examination begins.
Metallic foreign objects inside the patient, such as fixed dentures, artificial joints or metal plates, after fracture treatment are usually not dangerous. In the case of pacemakers, the magnetic field can cause malfunctions, so that certain factors must be taken into account for patients with pacemakers. Vascular supports such as stents or vascular clips, artificial heart valves, insulin pumps, hearing aids etc.
should always be indicated. Magnetic cards such as cheque or credit cards are deleted when entering the room where the magnetic resonance system is installed. Even a tattoo can be problematic for an MRT.
During the MRI examination, you lie on a movable couch, which at the beginning slowly moves into the magnet. The device has 70-100 cm openings on both sides. Depending on the region to be examined, the patient is either completely inside the device, e.g.
for an examination of the head, or only partially, e.g. for an examination of the knee joint. When taking the images, relatively loud, knocking noises are produced, which are sometimes perceived as disturbing. To attenuate these noises, the patient is given earplugs or closed ear protection.
Often you can also listen to music during the examination, just ask for it. There are patients who suffer from so-called “claustrophobia” (claustrophobia). If you have problems in this respect, you should discuss this with your family doctor or local radiologist beforehand.
In general, you can assume that the head is outside the device when examining body regions below the navel. In very difficult cases it may be necessary to use a short anaesthetic during the MRI.In this case, however, you must come to the examination with an escort, because you are not allowed to drive the car the whole day afterwards. Usually, an MRI examination takes between 20 and 40 minutes.
The exact duration depends on the type of MRI examination and also on the type of MRI: As a rule, it does not take longer than 15 to 20 minutes. In clinics, the start and duration of the examination may be delayed if, for example, emergencies have priority and must be examined first. Another reason for a longer duration is insufficient patient cooperation.
- Possible waiting times
- Complications and
- The cooperation of the patient.
- The MRI machine used, the clinical problem and the body part to be examined also play a role in the duration of the examination.
Some people cannot relax sufficiently or hinder the examination by not lying still. This can make it necessary to repeat the examination. In addition to the actual duration of the examination, the following must also be taken into account The preparation includes the removal of metallic objects such as piercings, jewelry, glasses or removable dentures.
Digital data carriers and credit cards may not be carried along either, as they are damaged by the magnetic field of the MRI examination. Waiting times may occur if, as already mentioned, other patients have priority, e.g. due to an emergency situation. Technical problems can also cause delays.
During the follow-up time, a first discussion of the findings is usually held. This can take different lengths of time depending on the type of findings. An MRI examination with contrast medium also takes slightly longer than an examination without contrast medium.
As a rule, two images of the structures to be imaged are taken, namely before and after the application of the contrast medium.
- Preparation and
- Follow-up time
It is usually not necessary to come to an MRI examination on an empty stomach. However, for special examinations or questions it may be necessary to perform the examination with an empty stomach.
This means that no food or drink may be consumed for a few hours before the examination. In most cases, 6 hours of fasting and 2 hours of fluid retention are necessary. After that, only a small amount of water may be drunk.
This is necessary, for example, for MRI examinations of the abdominal organs (intestine, gallbladder, stomach, etc.). However, one is explicitly informed in advance about such a special feature. If not communicated otherwise, it is not necessary to appear fasting. However, if you are unsure, it is advisable to ask during the clarification discussion prior to the examination.
