What is an MRI (magnetic resonance imaging)?
Magnetic resonance imaging (MRI) is a modern and very thorough procedure which allows to view sections of human internal organs in all dimensions. The scan is possible thanks to the magnetic properties of atoms of which the human body is built of. A strong magnetic field, pulses of short radio waves and a PC which transforms the obtained data into images are necessary to perform the procedure. The scan provides a non-invasive method for seeing the human internal organs and for evaluating the condition of each of the organs. The main advantage of an MRI is its safety for the patient. In contrast to a CT, an MRI does not require the use of x-ray. It is commonly believed that an MRI is a non-invasive procedure that does not strain the patient.
Does MRI use any harmful radiation?
An MRI requires a magnetic field instead of any ionizing radiation. Despite the fact that the strength of such magnetic field is 20 000 to 30 000 times bigger that the strength of gravity on Earth, it is completely safe for the human body.
What are the types of MRI scanners?
There are various types of magnets that create magnetic field of different strengths. The stronger the magnet is, the better results it yields. The quality of image is much higher when the magnetic field is strong; the best quality can be achieved with the use of high-filed MRI. Nowadays, the most commonly used MRIs have the magnetic field strength of 0.5T to 3T.
Only the MRIs which produce a very strong magnetic field can be used to perform such procedures as spectroscopy, function tests or ultrafast imaging of the vascular system.
What are function tests?
Diffusion MRI, perfusion MRI, brain function tests and spectroscopy are the types of procedures that show functions of the human body. Spectroscopy allows to measure the level of metabolites in the brain in a non-invasive way. This technique also allows to evaluate the biochemical processes in the particular part of the brain in any given moment. Usually the pathological focus shows metabolic changes much earlier, the morphological changes that are visible in diagnostic imaging can be seen only at a later stage. The changes on a biochemical level can be noticed thanks o spectroscopy.
On the other hand, functional MRI allows to evaluate the functions of particular parts of the brain. This is a very useful method, as based on such scan it is for example possible to determine how a surgery should be performed, not to damage the patient’s speech or hearing abilities during the procedure.
What are the indications for an MRI?
MRI has a very high tissue and dimensional contrast, which allows to see even the smallest structures in the human body. It is possible to scan all human organs using with the use of an MRI. The indications for an MRI related to the central nervous system include:
- tumors and cancers of the brain, brain stem and spinal canal
- demyelinating diseases (e.g. multiple sclerosis diagnostics)
- brain and spinal cord ischemia, especially in the early stage (first 4hrs) when they cannot be seen on a CT
- degenerative diseases, such as Alzheimer’s disease
- inflammations of the central nervous system - viral, bacterial, fungal and parasitic
- anomalies and cerebrovascular defects - aneurysms, vascular malformations - (MRA)
- diagnostic imaging of the pituitary gland
An MRI is a perfect method for performing scans of knee, shoulder, hip and ankle joints. The main indications for performing the scan are the post-injury changes in the joints. MRI allows to evaluate the conditions of ligaments and tendons, menisci, circumferential cartilage, joint cartilage, together with determining the presence of fluid in joint cavity. MRI is also used in the diagnostics of inflammations and in cancer staging in bones and soft tissue.
The scan also allows to diagnose the diseases in the abdomen, liver and pancreas. MRI is very useful for the diagnostics of pelvic organs - reproductive organs in women and prostate in men.
Are there any diseases that cannot be diagnosed with an MRI?
Despite the fact that an MRI is a very useful method and helps in the diagnosis of many diseases, it cannot be used to diagnose diseases that do not show any visible changes in the human body, such as schizophrenia or depression.
Why is a referral necessary to perform an MRI?
A referral is not necessary if the procedure is performed in a private facility. However, it is always better to have one, as it usually provides the initial diagnosis or some clinical indications for a diagnosis. It is necessary for the person performing an MRI to know which part of the body needs to be scanned, as the patient may not be able to provide such information. A different MRI technique can be used depending on the indications.
How often can an MRI be performed?
There are no restrictions on how often an MRI can be performed, as it is a completely safe procedure. It depends on the clinical requirements.
What are the contraindications for an MRI?
There are no biological contraindications for an MRI, it can be performed in every patient, regardless of their age and condition. However, there are some contradictions related to the presence of foreign bodies in the patient’s body - a pacemaker is a strict contraindication. Some possible contraindications include hip and knee prostheses, neurostimulators and other metal implants in the human body.
How do claustrophobic patients undergo an MRI?
Such patients usually feel uneasy during the procedure, as it involves being confined to a very narrow tunnel. The patient can take some tranquilizers before the procedure. There is also a possibility of sedating the patient for the time of the procedure. It is important to remember that is possible to press a dedicated button and contact the personnel that is performing the procedure. If the patient starts to feel uncomfortable, the procedure can be stopped.
How do I prepare for an MRI?
The procedure does not require any complicated preparations to be performed by the patients, however there are some rules that need to be respected. If the scan is an MRI with contrast, the patient should not eat anything at least 4 hours before the procedure. The patient should also wear loose-fitting, comfortable clothes, as the procedure requires to lie in a steady position for a long period of time. The clothes should not have any metal elements, such as buttons, zippers, etc. A belt, watch, keys, mobile phone and credit card should be left in a changing room, before entering the room with the MRI scanner, so that they are not damaged.
Women should not wear makeup (as it may contain non-ferrous metals particles) or apply hairspray before the procedure, as it may affect the image being produced and obstruct a correct diagnosis.
Prescribed drugs should be taken as usual.
If the patient has any previous scans (images with interpretation) and medical history (discharge papers) available, he/she should bring them to the procedure as well.
What happens during an MRI?
First, the patient receives a questionnaire which needs to be filled in. Then the patient goes to a changing room where clothes and other belongings can be taken off and left. Next, the patient enters the room where the MRI is, lies down on the table and enters the MRI scanner. The procedure is painless, usually lasts between one to three quarters. The patient should not move during the procedure. A comfortable position is important, as the patient needs to remain still during the whole scan.
Compiled Bożena Kubas, MD