A magnetic resonance imaging (MRI) scan is a common procedure used by hospitals around the world. MRI uses a strong magnetic field and radio waves to create detailed images of the organs and tissues within the body.
The development of MRI revolutionized the medical world. Since its discovery, doctors and researchers have refined techniques to use MRI scans to assist in medical procedures and also help in research.
Contents of this article:
Fast facts on MRI scanners
Here are some key points about MRI scanners. More detail and supporting information is in the main article.
- MRI scans are a non-invasive and painless procedure
- Raymond Damadian created the first MRI full body scanner, which he nicknamed the "Indomitable"
- The cost of an MRI scanner starts at $150,000
- Japan has the most MRI scanners, with 46.5 per one million citizens.
What is an MRI scan?
An MRI scan uses a large magnet, radio waves, and a computer to create a detailed cross-sectional image of the patient's internal organs and structures.
The scanner itself typically resembles a large tube with a table in the middle, allowing the patient to slide into the tunnel.
What are MRI scans used for?
An MRI scanner can be found in most hospitals and is an important tool to analyze body tissues.
The development of the MRI scan represents a huge milestone for the medical world, as doctors, scientists, and researchers are now able to examine the inside of the human body accurately using a non-invasive tool.
The following are just some of the examples where an MRI scanner is used:
- Abnormalities of the brain and spinal cord
- Tumors, cysts, and other abnormalities in various parts of the body
- Injuries or abnormalities of the joints, such as back pain
- Certain types of heart problems
- Diseases of the liver and other abdominal organs
- Causes of pelvic pain in women (e.g. fibroids, endometriosis)
- Suspected uterine abnormalities in women undergoing evaluation for infertility
Preparing for an MRI scan
There is little to no preparation required for patients before an MRI scan. On arrival at the hospital, doctors may ask the patient to change into a gown. As magnets are used, it is critical that no metal objects are in the scanner, so the patient will be asked to remove any metal jewelry or accessories that may interfere with the machine.
Sometimes, patients will be injected with intravenous (IV) contrast liquid to improve the appearance of a certain body tissue.
The radiologist will then talk the individual through the MRI scanning process and answer any questions they may have about the procedure.
Once the patient has entered the scanning room, they will be helped onto the scanner to lie down. Staff will ensure that they are as comfortable as possible by providing blankets or cushions.
Earplugs or headphones will be provided to block out the loud noises of the scanner. The latter is very popular with children as they can listen to music to calm any anxiety.
During an MRI scan
Once in the MRI scanner, the doctor will speak via the intercom to ensure the patient is comfortable. They will not start the scan unless the patient is ready.
During the scan, it is imperative to stay still. Any movement will disrupt the images created, much like a camera trying to take a picture of a moving object. Loud noises will come from the scanner, which is perfectly normal. If the patient feels uncomfortable during the procedure, they can speak to the doctor via the intercom and request the scan be stopped.
After an MRI scan
After the scan, a radiologist will examine the images to check whether any further images are required. If the radiologist is satisfied, the patient can go home. The radiologist will prepare a short report for the doctor, who will make an appointment to discuss the results.
How does and MRI scanner work?
An MRI scanner contains two powerful magnets; these are the most important parts of the equipment.
The human body is largely made of water molecules, which are comprised of hydrogen and oxygen atoms. At the center of each atom lies an even smaller particle called a proton, which serves as a magnet and is sensitive to any magnetic field.
Normally, the water molecules in our bodies are randomly arranged, but upon entering an MRI scanner, the first magnet causes the body's water molecules to align in one direction, either north or south.
The second magnetic field is then turned on and off in a series of quick pulses, causing each hydrogen atom to alter its alignment and then quickly switch back to its original relaxed state when switched off. The magnetic field is created by passing electricity through gradient coils, which also cause the coils to vibrate, resulting in a knocking sound inside the scanner.
Although the patient cannot feel these changes, the scanner can detect them and, in conjunction with a computer, can create a detailed cross-sectional image for the radiologist to interpret.
Functional magnetic resonance imaging (fMRI)
Functional magnetic resonance imaging or functional MRI (fMRI) uses MRI technology to measure brain activity by monitoring blood flow in the brain. This gives an insight into the activity of neurons in the brain as blood flow increases in areas where neurons are active.
This technique has revolutionized brain mapping by allowing researchers to assess the brain and spinal cord without the need for invasive procedures or injections of drugs.
fMRI helps researchers learn about the function of a normal, diseased, or injured brain.
Functional MRI is also used in clinical practice as, unlike standard MRI scans which are useful for detecting structural anomalies in tissues, a functional MRI scan can help detect anomalous activity in those tissues. As such, it is used to assess the risks posed by brain surgery by helping a surgeon to identify the regions of the brain involved in critical functions such as speaking, moving, sensing, or planning.
Functional MRI can also be used to determine the effects of tumors, stroke, head and brain injury, or neurodegenerative diseases such as Alzheimer's.
MRI frequently asked questions
It is important to stay still during the scan.
How long will an MRI scan take?
MRI scans vary from 20-60 minutes depending on what part of the body is being analyzed and how many images are required.
If, after the first MRI scan, the images are not clear enough for the radiologist, the patient may be asked to undergo a second scan straight away.
I have braces/filings, should I still undergo the scan?
Although braces and fillings are unaffected by the scan, they may distort the image. The doctor and radiographer will discuss this beforehand. The MRI scan may take longer if additional images are required.
Can I move while I am in the MRI tunnel?
No, it is important to stay as still as possible while in the MRI scanner. Any movement will distort the scanner and, therefore, the images produced will be blurry. In particularly long MRI scans, the doctor may give a short break halfway through the procedure.
I am claustrophobic, what can I do?
The doctor and radiologist will be able to talk the patient through the whole procedure and address any anxieties. Open MRI scanners are available in some locations to help patients with claustrophobia.
Do I need an injection of contrast before my MRI scan?
Some patients may need to have a contrast agent injected before the scan to improve diagnostic accuracy by highlighting certain issues, such as inflammation.
Can I have an MRI scan if I am pregnant?
Unfortunately, there is not a straight answer to this question. The doctor should be informed before the scan. There has been relatively little research on the effect of MRI scans on pregnancy. However, guidelines published in 2016 have shed more light on the issue.
It is recommended that MRI scans should be restricted during the first trimester unless the information is considered essential. MRI scans taken during the second and third trimester are safe at 3.0 tesla or less.
The guidelines also state that inadvertent exposure to MRI during the first trimester has not been associated with long-term consequences and should not raise clinical concern.