Synonyms
English
- Magnetic Resonance Imaging
- Magnetic Resonance Imaging
- Nuclear magnetic resonance examination
- NMR (nuclear magnetic resonance)
- MRI (magnetic resonance imaging)
Radiation exposure during an MRT examination
The advantage of magnetic resonance imaging over computed tomography and X-rays is that there is no radiation exposure for the patient. MRI images are created by generating a strong magnetic field that affects the hydrogen atoms in the human body. These then emit radio waves at different levels, depending on the type of tissue involved.
These waves are detected by a computer and processed into sectional images. Since there is no radiation exposure, there are no known side effects during an MRI examination. Especially for young patients an MRI is a good method to visualize the soft tissues without the risk of radiation exposure.
Do I have to be sober for an MRI examination?
As a rule, the patient does not have to appear fasting for magnetic resonance imaging. Both eating and drinking is allowed in advance. An exception is the examination of certain organs in the abdomen (MRI abdomen).
Before an MRI examination of the intestine, bile or stomach (see: MRI of the stomach), for example, the patient should be fasting so that the images can be assessed well. During these examinations it is also often necessary to drink a contrast medium before the examination. The patient will be informed beforehand whether or not he/she must come to the examination on an empty stomach.
Duration of an MRT examination
The duration of a magnetic resonance imaging examination is variable. Depending on which area is to be imaged and how many images are to be taken, it may take shorter or longer. However, the examination itself usually takes about 15 to 30 minutes.
Added to this are the preparation time and the waiting time. Preparation involves removing all metal parts from the body or clothing. In addition, the patient must be placed on the examination couch and special pillows may have to be used to hold the examined body part in place.
If the administration of contrast medium is necessary, the examination will take longer, since this is usually injected into the arm vein after the first pass before a second pass starts. Magnetic resonance imaging (MRI), also known as magnetic resonance imaging (MRI), is a modern sectional imaging procedure that uses the principles of what is known as nuclear magnetic resonance. In contrast to computer tomography, for example, strong magnetic fields and radio waves are used instead of X-rays (see X-rays) to generate the images.
With the help of this MRI examination, layered images of almost any part of the body can be generated in a relatively short time in a non-invasive manner (without intervention in the body) at any angle and direction. This information is available in digital form, which enables the radiologist to generate various views of the examined body part after the examination with the help of powerful computers. The central core of an MRI (magnetic resonance imaging) system is a superconducting electromagnet weighing several tons, usually cooled with liquid helium.
Transmitting and receiving antennas are built into its inner wall. If necessary, additional antenna coils are added to the magnetic resonance imaging system depending on the body region to be examined. There are specially shaped coils for special examinations, e.g. for the examination of the head, knee joint, spine or (female) breast (MR mammography).
To ensure that the examination is not disturbed by other radio waves, the MR examination room is shielded by a Faraday cage. The human body consists of countless tiny biological magnets due to the abundant presence of hydrogen protons. This is used in magnetic resonance imaging.
Due to their rotation (nuclear spin) of these hydrogen protons, a magnetic moment develops and the protons behave like small magnetic gyroscopes that align themselves in an externally applied strong magnetic field according to the field lines of the magnetic field.Magnetic resonance imaging (MRI) essentially involves three steps:First, a strong, stable, homogeneous magnetic field of 1 – 3 Tesla is generated around the body (10,000 – 30,000 times stronger than the earth’s magnetic field), thereby achieving a stable alignment of the protons. As a second step of the MRI examination, this stable alignment is changed by electromagnetic high-frequency energy in the form of a radio signal at a certain 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. Above is an example of an open MRT (magnetic resonance imaging).
