Magnetic resonance imaging (MR examination) is a recently developed procedure. In a strong and constant magnetic field the particles in body tissues line up and get aligned. During the procedure, the magnetic field in the area being examined changes in a pre-set manner, which causes the resonance of particles to differ from each other. The MRI device uses this difference to distinguish the different parts of the affected organ. The particles required for imaging need to be excited with the help of radio frequency waves. In terms of the most commonly used signal, their wave length is at the bottom of the Eastern ultra-short wave band; therefore, it has no harmful biological effect. After excitement, the tiny particles realign back into place. As they do so they reflect the absorbed radio signals, which can be detected with an antenna. The signals emitted from different body tissues vary in time and parameters. The device measures the time and other parameters of realignment and transforms them to get a picture. The different tissues behave in different ways, which provides detailed structural information on the examined organs. It is possible to visualize several abnormalities that change tissue structure in organs. Such abnormalities include tumors and their metastases, inflammatory processes and coagulation disorders. Vessels can also be visualized with MRI, which will provide plenty of information without the patient having to undergo harmful and uncomfortable interventions. During the examination patients are placed into a strong magnetic field, which has no potential harmful effects. Instead, imaging here relies on sending the above-mentioned length radio waves and receiving the signals emitted by the tissues. When patients arrive for examination, they should remove everything from their body that may contain metal (e.g. jewelry, watch, hair clip, brooch, necklace, belt, suspenders, glasses, zip fastener, hook, removable denture, hearing aid, mobile phone, credit card) as they may impair the quality of the procedure, or they may break loose in the magnetic field. In the examination room there is a constant magnetic field. Patients need to enter this room. Before patients enter, the staff should make sure there is no magnetizable (metallic) material on or in the patient’s body. Patients are also informed on the above with the help of an information sheet provided before the examination, which is highly recommended to be read carefully. In the examination room patients should lie down on the examination table. The assistant will place the radio frequency receiving coil on the body part being examined. Patients should lie motionless during the measurements. Magnetic resonance imaging will produce cross-sectional images which enables the radiologist to set up a reliable diagnosis of the patient’s condition. The huge amount of measurement information is transmitted to a computer, which performs different calculations and converts the information into an image. This way MR exams take relatively long time; one sequence may take as many as 15-30 minutes. For some MRI exams, a contrast agent may be injected into a vein to help obtain a clearer picture of the anatomical structure being examined; this way the individual organs and pathological lesions are easier to distinguish. During an MRI examination patients will have to lie still, preferably completely relaxed on a moveable table. The examination table will slide into a large and brightly illuminated “tube” and the part to be examined will get into the centre of the magnetic field. During the examination, the patient is close contact with the physician performing the examination, and the operating staff; they can communicate via a microphone, and the patient is also monitored with a camera, through a window. It is also possible for the patient to have a relative, friend or an accompanying person present during the whole procedure in the examination room; this, however, requires the prior consent of the Centre. Patients can take their usual medications and can also drink before the examination. They do not have to show up with an empty stomach for the examination but should not eat 2 hours before the exam, just in case contrast agent administration becomes necessary. Patients should tell in advance if they have any metal implant in their body (e.g. pacemaker, which is a device to set the heart rhythm; implanted joint prosthesis; implanted prosthetic heart valve; middle-ear prosthesis; metal device implanted during trauma surgery; implanted pump; etc.) or if they have had any accident where a metal shard, fragment or shrapnel may have got into their body or eyes. MRI is reserved for use in pregnant patients only to address very important problems. While no effects have been demonstrated on the fetus, some of its effects are still not completely unambiguous; therefore, it is recommended that MRI scans be avoided as a precaution.
It is good to know four characteristic features of MR examinations before one undergoes such a procedure:
- Confined space: some patients may feel confined and closed-in, which is usually not felt if a relative is present. Patients should remember that they are not closed in the device, and they are in close contact (audio and video) with the staff.
- Noise: when taking the measurements, the device may make loud noises commonly referred to as clicking and beeping, which may be heard for 3-10 minutes. It is exactly in this time that the actual examination takes place, so this is the time when patients definitely need to lie motionless.
- Warming: the temperature in the magnet is around 22-25 degrees, the examination room is air conditioned.
- Examinations are quite lengthy: probably the most difficult part of the MR exam is that patients need to lie motionless. Patient movement may significantly deteriorate the quality of the images. Should you have any questions or concerns related to the exam, feel free to ask the physician performing the examination or the staff, who will be ready to answer your questions.