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Magnetic resonance imaging
What is magnetic resonance imaging?
What is an MRI? Many patients ask this when the doctor orders such an examination. The abbreviation MRT stands for magnetic resonance imaging, also known as magnetic resonance imaging (magnetic resonance imaging) or, colloquially, nuclear spin. It is a frequently used imaging method, with the help of which precise cross-sectional images of the body are created in high resolution. The doctor can use these images to assess organ structures and functions. If the whole body is examined using magnetic resonance imaging, one speaks of a whole-body MRI. However, only individual parts of the body or organs can be examined. Examples:
- Small intestine MRI (Sellink, Hydro MRI)
- Abdominal MRI (abdomen)
- Coronary arteries (cardiac MRI, sometimes under stress as stress MRI)
- Skull (cranial) MRI (cMRT)
- Joints (for example, MRI shoulder or knee joint)
Further information: MRI head
You can read in the article MRI: Head when an MRI of the head makes sense and how the examination works.
Further information: MRI - knee
You can find out which diseases and injuries in the knee joint can be determined using magnetic resonance imaging in the article MRI: Knee.
Further information: MRI - cervical spine
You can read how magnetic resonance imaging of the cervical spine works and when it is carried out in the article MRI: Cervical spine.
MRI: functionality and physical basics
Magnetic resonance tomography uses the fact that atomic nuclei rotate around their own axis. This rotation is called nuclear spin and it creates a small magnetic field around each nucleus. The hydrogen atoms found everywhere in the human body also show this nuclear spin. Usually their axes of rotation point in different directions. But that changes with magnetic resonance imaging:
The MRI machine (magnetic resonance tomograph) is usually a large tube into which the patient is pushed on a couch. The ring-shaped magnet tunnel creates a strong magnetic field along which the hydrogen atoms align in parallel in the patient's body. Then the MRI machine sends out short radio wave impulses that briefly move the hydrogen atoms out of their position. In addition, the atoms take up some energy. After each pulse they return to the parallel alignment. This process is called relaxation. The energy previously absorbed, which the hydrogen atoms release again, is recorded. Since the different tissues in the body have different water contents, different signals result from which the computer calculates the MRI images.
The radiologist calls the electromagnetic pulses emitted by the MRT machine sequences. The various sequences represent tissue differently. Frequently used sequences in magnetic resonance imaging are, for example:
- Spin echo sequence (SE)
- Gradient echo sequence (GRE) (for calcium deposits or bleeding)
- Fluid attenuated inversion recovery (FLAIR-MRI for inflammatory diseases such as multiple sclerosis)
- Spin echo fat saturation (SE fs)
MRI: T1 / T2 weighting
As described, the return of the atoms to their starting position is called relaxation. The computer uses this to calculate the sectional images. Depending on whether it is based on the longitudinal or transverse alignment of the atoms, one speaks of a T1 or T2 weighting. With the T1 weighting, fatty tissues appear lighter than their surroundings, with the T2 weighting liquids are shown.
Magnetic resonance imaging with contrast agent
For some questions, the doctor has to give the patient a contrast medium before the MRI scan. Most of the time, the contrast agent is simply injected into a patient's vein, where it spreads throughout the body via the bloodstream. With Hydro-MRI for exams of the digestive tract, the patient can also drink the contrast agent; it then spreads in the gastrointestinal tract. With Sellink MRI, the patient can receive the contrast medium through a small intestinal probe.
Further information: MRI contrast media
You can read everything you need to know about the use of contrast media in magnetic resonance imaging in the article MRI contrast media.
Difference: CT - MRI
An important difference (MRT / CT) concerns the radiation exposure: Computed tomography (CT) works with X-rays, which means radiation exposure for the patient. In magnetic resonance tomography, on the other hand, magnetic fields and radio waves are generated and these do not contain any radiation.
The disadvantage is the greater time required for an MRI: the duration of the examination is between 30 and 45 minutes. Computed tomography, on the other hand, is significantly faster with an average duration of 10 minutes and is therefore also the method of choice in emergencies in which the doctor needs a cross-sectional image of the body as soon as possible. The decision of whether a patient will benefit more from an MRI or CT must always be made by the doctor depending on the suspected diagnosis.
When do you perform magnetic resonance imaging?
In contrast to CT, which can display particularly water-poor structures such as bones, magnetic resonance imaging is the method of choice if you want to examine soft tissues more closely. It is therefore often used in cancer diagnostics, for example to assess the course of a tumor disease or to locate metastases. The attending physician also often orders an MRI in the following cases:
- MS (multiple sclerosis)
- inflammatory diseases of the bone
- inflammatory diseases of the organs (pancreas, gall bladder, etc.)
- Abscesses and fistulas
- Vascular malformations and bulges (such as aneurysms)
- Joint damage (osteoarthritis, injuries to tendons, cartilage and ligaments)
Examination is important for these diseases
Read here for which diseases the examination can be useful:
What do you do with magnetic resonance imaging?
In advance, the doctor will explain the aim of the examination, the procedure and possible MRI side effects. You will also find out whether you have to appear on an empty stomach for an examination (for example, if you have an MRI of the small bowel).
For the examination you have to take off all metal-containing and magnetizable or electronic objects, for example jewelry, piercings, keys, coins, hair clips, hearing aids, removable dentures, brassieres (with metal brackets), glasses, watches, magnetic cards (credit cards), belts and cell phone. The strong magnetic field generated by the MRI machine can heat such objects (risk of burns) or accelerate them like projectiles. Conversely, the objects may interfere with the magnetic field, which has a negative effect on the image quality.
If you have a pacemaker or other implanted device, you should definitely tell your doctor about it before the MRI scan. Since the function of the sensitive device could be disturbed by the magnetic resonance tomography, the doctor must decide whether you are allowed to go through the examination at all. If in doubt, he must ask the manufacturer beforehand.
In addition, metal parts in the body can shift during magnetic resonance imaging or heat up so much that burns can occur. Particular caution is therefore required with:
- Metal prostheses
- nails, plates or screws in the body (e.g. inserted after bone fractures)
- Contraceptive IUDs
- Metal splinters left in the body after an accident or gunshot wounds
Before the MRI scan, inform your doctor about any tattoos or permanent make-up, because some of the dyes also contain metal particles. In the MRI, this can cause skin irritation and even burns. Normal make-up may need to be removed prior to magnetic resonance imaging.
For the examination you have to lie down on the mobile, narrow couch in front of the MRT machine. Then you will be pushed into the tube. As long as the examination is ongoing, you should lie as still as possible so that sharp images can be created. You may have to hold your breath briefly in between - you will receive instructions to this effect over a loudspeaker.
The MRI examination is accompanied by loud knocking noises, which are caused by switching the magnetic coils on and off. You will therefore receive hearing protection or soundproof headphones with music in advance.
MRI: claustrophobia in the tube
If you suffer from claustrophobia, you should tell the doctor beforehand. He can give you an anti-anxiety medication so that you can bear the tightness in the tube better. If you are extremely claustrophobic, magnetic resonance imaging can also be performed under short-term anesthesia. This also applies to an MRI in children. Some clinics and practices also offer the so-called open MRI, in which the patient is less cramped.
A open MRI (open MRI) is a good alternative for patients who suffer from claustrophobia. Even patients who are very overweight, who are simply difficult to examine in a conventional MRI machine for reasons of space, benefit from open MRI.
Another particularly important advantage is that the doctor has access to the patient at all times through the open tube. For example, under image control, he can take samples from suspected cancerous nodes or administer locally effective medication.
Not all radiological practices and clinics have an open magnetic resonance tomograph. If you prefer to be examined in an open system, speak to your doctor about it. He or she may be able to recommend a suitable practice. Alternatively, you can do your own research on the Internet to find out which radiologists offer an open MRI.
Magnetic resonance tomography: special procedures
A special case is the so-called upright MRI, in which the patient does not lie on a couch, but can sit or stand in an open system. In this way, the doctor can assess the spine in particular under the loads that prevail under normal conditions.
For certain questions, the doctor also uses combined methods, for example PET / MRT, in which metabolic processes are also made visible. PET stands for positron emission tomography.
What are the risks of magnetic resonance imaging?
Magnetic resonance imaging is a very safe, painless diagnostic tool. Only pregnant women in the first trimester and patients with sensitive implants or metal parts in their bodies receive an MRI scan only when absolutely necessary.
Side effects that can result from the contrast agent are:
- Feeling hot
- a headache
- Tingling or numbness
- Kidney dysfunction
- Intolerance reactions
If you have put down all metal-containing and magnetizable objects as far as possible in advance of the magnetic resonance imaging, no dangers (such as burns) are to be expected from this side.
MRI & pregnancy
So far, no harmful effects of magnetic resonance imaging on an unborn child have been proven. However, since it cannot be ruled out that the radio impulses endanger the embryo in the first three months of pregnancy, the examination should only be carried out in justified cases. According to current knowledge, an MRI during pregnancy at a later stage is not dangerous.
More about the symptoms
The examination can be useful if the following symptoms occur:
What do I have to consider after an MRI scan?
If you have been given a sedative for magnetic resonance imaging, you should not drive for at least 24 hours. If the magnetic resonance tomography takes place on an outpatient basis, it is best to organize someone who can pick you up beforehand.
The recorded MRT images are available immediately after the examination. However, the doctor must first assess this and make a report. You will then usually receive the MRI result in the post within a few days, sometimes you have to pick it up yourself from the radiological practice. You will also receive a CD on which the sectional images are saved. Bring the findings and CD of the Magnetic resonance imaging at the next appointment with your treating doctor.
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