MRI
The development of MRI revolutionized the medical world. Since its discovery, doctors and researchers have refined techniques so as to use MRI scans to not only assist in medical procedures but also aid in research
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.
An MRI scan differs from CT scans and X-rays because it does not use ionizing radiation that can be potentially harmful to a patient.1
Background of the MRI scanner
The first full-body MRI scanner was created by Prof. Raymond Damadian in 1977 and took nearly 5 hours to produce the first ever full body scan of a human. Dr. Ramadan nicknamed the first MRI scanner the "Indomitable" and it is currently housed in the Smithsonian Institute.2
The idea for MRI was initially conceived by Damadian in 1971 after he recognized that under nuclear magnetic resonance certain mouse tumors would display elevated relaxation times compared with normal tissues in vitro.
How does an MRI scan work?An MRI Scanner.
An MRI scanner can be found in most hospitals and is an important tool to analyze body tissues.
An MRI scanner contains two powerful magnets, which represent the most critical part 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 causes 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.
What are MRI scans used for?
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 insides of the human body accurately using a non-invasive tool.
The following are just some of the examples where an MRI scan 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.
What happens before an MRI scan?
There is little to no preparation required for patients before an MRI scan. On arrival at the hospital, doctors may ask you to change into a gown. As magnets are used, it is critical that no metal objects are in the scanner, meaning that you 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 you through the MRI scanning process and answer any questions you may have on the procedure.
Once you have entered the scanning room, you will be helped onto the scanner to lie down. Staff will try to ensure that you are as comfortable as possible by providing blankets or cushions. You will also be offered earplugs or headphones 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.
What happens during an MRI scan?
Once in the MRI scanner, the doctor will speak to you to via the intercom to ensure you are comfortable. They will not start the scan unless you are ready.
During the scan, it is imperative you try your best to stay still. Any movement will disrupt the images created, much like a camera trying to take a picture of a moving object. You will hear some loud noises coming from the scanner, which is perfectly normal.
If you feel uncomfortable during the procedure, you can speak to the doctor via the intercom and request the scan be stopped.
What happens after an MRI scan?
After the scan, a radiologist will examine your images to check whether any further images are required. If the radiologist is satisfied, you can simply get changed and go. The radiologist will prepare a short report for your doctor, who will make an appointment with you to discuss the results.
What is a functional MRI scan?
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 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
How long will an MRI scan take?
MRI scans vary from 15-60 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, you 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 still may distort the image. Consult your doctor and radiographer beforehand. The MRI scan may take longer if additional images are required.
Can I move while I am in the MRI tunnel?
No, you will be asked to remain as still as possible while in the MRI scanner. Any movement will distort the scanner and, therefore, the images produced will be blurry. In cases when you have a particularly long MRI scan, the doctor may give you a short break halfway through the procedure.
A male patient about to undergo an MRI scan.
Some may find the idea of an MRI scan claustrophobic. Your radiologist will be able to answer any questions you may have. I am claustrophobic, what can I do?
You should speak to the doctor and radiologist beforehand. They will be able to talk you through the whole procedure and address any anxieties you may have. Open MRI scanners are available in some locations to help with patients suffering from claustrophobia.
Do I need an injection of contrast before my MRI scan?
You may need to have a contrast agent injected before your MRI scan if your doctor feels it is necessary to improve diagnostic accuracy by highlighting certain issues, such as inflammation.
Can I have the MRI scan if I am pregnant?
Unfortunately, there is not a straight answer to the question above. If you are pregnant, you should inform your doctor before the scan. There has been relatively little research on the effect of MRI scans on pregnancy. However, guidelines published in 2014 have shed more light on the issue.
It is recommended that MRI scans should be restricted during the first trimester unless the information is deemed "clinically imperative." 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.
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