Magnetic resonance imaging (MRI)

MRI is an imaging procedure using strong magnetic fields and radio waves. It is also called nuclear spin tomography. Unlike computed tomography (CT), it does not involve radiation exposure. Similar to CT, radiologists create detailed, three-dimensional cross-sectional images of the inside of the body. The method is painless.

Overview

MRI takes advantage of the fact that if a strong magnet is applied to the human body, its water molecules (hydrogen atoms, to be precise) arrange themselves in parallel. When radio waves hit these parallel hydrogen nuclei, their orientation changes. After the radio wave pulse subsides, they return to their initial parallel position. The extent of this deflection can be recorded and a computer can convert the data into layered images.

By means of these MRI images, doctors can diagnose diseases and injuries of organs, soft tissues and other tissues very well. Hard structures such as bones or joints can also be displayed. Depending on their water content, the structures and tissues appear lighter or darker on the MRI images.

Radiologists often work with a contrast medium containing gadolinium, which they inject into the vein. This enables them to distinguish different tissues even better, for example in the case of tumors, inflammation, signs of wear and tear, or injuries.

In neuroradiology MRI is used to diagnose a wide variety of diseases and injuries. Some examples:

• Diseases of the brain, e.g. stroke, brain tumors, vascular malformations, inflammations, injuries after accidents.
• Diseases of the spinal cord
• Vascular changes in arteries and veins, e.g. constrictions or occlusions
• Joint diseases, intervertebral disc wear, vertebral body fractures

Magnetic resonance imaging can also be combined with other examination methods. One example is positron emission tomography (PET-MRI, e.g. for cancer).

Our special examinations

• MR perfusion assessment
• MR spectroscopy
• Functional MRI (fMRI)
• Diffusion Tensor Imaging (DTI) and fiber tracking
• MR morphometry
• MRI for neuronavigation
• Intraoperative MRI
• MR-guided focused ultrasound (MRgFUS)
• MR flow measurement intracranial vascular (NOVA)
• MR vessel wall imaging
• MR liquor flow measurement
• MRI in neonates
• MRI under anesthesia
• MRI in the presence of metallic/functional implants
• High-resolution cranial nerve imaging
• High resolution hydrops imaging
• Dynamic MRI of the temporomandibular joints

Advantages and disadvantages

Advantages

• It does not involve radiation exposure (similar to ultrasound techniques).
• MRI does not cause pain.
• MRI can be used to diagnose almost all diseases, injuries and changes in organs and tissues.
• The method is particularly well suited for brain and spinal cord imaging, and for soft tissues such as muscles, etc.
• Magnetic resonance imaging can also be performed on pregnant women
• It is considered safe. However, you should always discuss with your doctor whether the MRI is really necessary.

Disadvantages

• The procedure is relatively expensive.
• MRI may not be possible in case of fixed metal implants in the body.
• Lying in the tube is often very scary for people with claustrophobia (fear of being in confined spaces).
• An MRI takes longer than e.g. performing an ultrasound or CT scan.
• Contrast agents containing gadolinium can sometimes come with side effects, such as a temporary feeling of warmth or cold, headache, discomfort, tingling, or skin irritation. Rarely allergic reactions to this contrast agent occur.

Course of treatment

• You lie down as comfortably as possible on a machine couch, and the radiographer will push it into the magnetic resonance scanner.
• During the examination, you will be alone, but will remain connected to the staff in the adjacent room via an intercom system. You can communicate with the radiographer at any time.
• You will be given an emergency button, which you can hold in your hand. Especially if you are claustrophobic, this can contribute to a feeling of safety while you lie in the narrow tube. If you press the button, you can stop the examination at any time – however, the scans performed at that time must be repeated.
• The examination is quite noisy with the machine producing loud pounding and tapping noises. Therefore, you will be given headphones to protect your ears. The machine produces loud pounding and tapping noises.
• During the examination, you must lie as still as possible and not move.
• Sometimes doctors inject a contrast agent containing gadolinium (a metal) into the vein to increase the tissue’s contrast. Because of potential gadolinium buildup in the brain, the European regulatory agency EMA has banned certain linear contrast agents or allows them only in exceptional cases. In Switzerland, three linear gadolinium preparations are still in use, but radiologists rarely resort to them. Use of macrocyclic contrast media, on the other hand, is permitted since these bind the gadolinium better than the linear agents. After their use, gadolinium residues can still be detected in the brain but it is not certain if their levels are harmful. Additionally, physicians always use contrast media in the smallest possible quantities.