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What Is MRI (Magnetic Resonance Imaging)?

L. S. Wynn
By L. S. Wynn
Updated: Mar 03, 2024

Magnetic resonance imaging (MRI) uses powerful magnetic fields and radio wave energy to take pictures of the inside of an object. This method of scanning was developed primarily for use in medicine as a way to take images of structures in a patient's body, but it also has been used to study objects such as fossils and historical artifacts. An MRI is able to provide images that give information that previous scanning technology, such as X-ray, computed tomography (CT) and ultrasound cannot.

How It is Done

When an MRI is necessary, the patient lies on an imaging table that slides into a large MRI scanner. Powerful magnetic fields are administered to align the nuclei within the atoms of the patient's body. Next, radio frequency pulses are applied. The nuclei release some of the radio frequency energy, and these emissions are detected by the MRI equipment. With this data, a computer can generate a highly detailed view of tissues within the body immediately after the scan.


Earlier imaging technologies, such as X-rays, were able to detect dense tissues, particularly bones. MRI scans give doctors the ability to better view all sorts of body structures, including soft tissues. Magnetic resonance imaging also is able to differentiate between different types of soft tissues better than other scanning technologies. The digital images that are rendered by the computer can be two-dimensional or even three-dimensional.


Perhaps the most well-known use of magnetic resonance imaging is in the diagnosis of injuries to muscles, ligaments, tendons or cartilage, such as knee injuries or pulled muscles. MRIs are frequently used to detect cancers that would otherwise be difficult to diagnose, such as mesothelioma. The ability to detect abnormalities, such as cancers at their early stages, has put magnetic resonance imaging at the forefront of the battle against many diseases. MRIs also can be used to look for a wide range of other conditions, including brain injuries, damage to organs in the abdomen and spinal injuries.

Effects on Patients

It generally is believed that patients are not harmed by undergoing an MRI exam, because radiation is not used. There are no known side effects, but patients who have pacemakers or certain other metallic implants are not eligible for these scans. Exams typically take 30 to 60 minutes. Early models of MRI scanners required patients to be placed in confined positions, but newer versions use an open design that is much more spacious and comfortable. The patient is able to resume normal activity immediately after the test.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By anon975201 — On Oct 25, 2014

I recently had an MRI scan and forgot to take off my gold/diamond eternity ring. I felt some quite strong vibrations on the ring and told the nurse who said it was not a problem. Since coming out from the MRI, I have noticed that one of the diamonds is damaged. Could the MRI do this? Or is it a coincidence? Could a microscopic flaw or impurity in the diamond have caused this in the MRI scanner? Thank you

By anon285513 — On Aug 16, 2012

I had an MRI last week. Can an MRI disturb the surgical staples that were used during my VATs surgery?

During the last part of the scan I could feel a kind of pulsing in my left side where the staples are.

By anon251841 — On Mar 02, 2012

I just had an MRI on my shoulder and my engagement ring/wedding ring/enhancer (all engraved with "14k") were vibrating - what the heck? Does this mean that they aren't real and they were illegally engraved as 14k?? They were purchased at Kay Jewelers!

By anon145679 — On Jan 24, 2011

are silver necklaces not dangerous, if found to be on the body later?

By cleevn — On Jan 19, 2011

I had an MRI today and forgot to take off my gold and diamond rings (x3). The scan was of my spine and I had my hand on my abdomen. They checked for my watch, hair pins etc, but nobody mentioned the rings. I didn't think about it until I was on the way home. Will the images be OK?

By anon137490 — On Dec 28, 2010

My son is now two years and four months and yet he still cannot walk. He had experienced a seizure last November. The pediatrician advised he had to undergo EEG. When I got the result, I was shocked and depressed. His pediatrician advised him to have MRI.

I don't know what to do. Is my child a special needs child? Does he need to undergo an MRI? Please advise because right now I don't know how to help with my son's condition. --Sky

By anon130782 — On Nov 29, 2010

I had surgery for a cerebral aneurysm in 1998 and they used titanium clips. I was told that it would not be a problem with these clips. Really scared would really appreciate feedback.

By anon129449 — On Nov 23, 2010

I was supposed to have an MRI on my shoulder, but was told they could not get an image. When the tech showed me, it was completely blacked out where my joint and tissues should be. Can anyone tell me why this would be?


By anon116846 — On Oct 08, 2010

My dad had triple bypass surgery in 1990. At that time, they placed surgical staples in his sternum and leg. Is it safe for him to have an MRI procedure?

By anon77012 — On Apr 12, 2010

In the 1960's, bone marker implants made of tantalum were pounded into my gums before I had orthodontia. I'm wondering if I can have an mri?

By kRussell909 — On Mar 18, 2010

My name is Kurt. My girlfriend has disc degeneration with annular tear and disc protrusion at L4/L5. Her most recent MRI report that the doctor saw did not match what we saw in the films. Is this medical malpractice? Thank you.

By anon27009 — On Feb 22, 2009

After 6 weeks staples and metal implants will become encased with scar tissue they will not come out or move but with that said if you have a metallic implant in a muscle, heart,eye or brain it may move if not safe for a MRI scanner. You must bring your implant card and ask for verification from the technologist not technician.

We have gone to college to earn this title and we do take offense to not being referred to as a professional. A technologist has gone to school for two or four years depending on their college of choice.

Your wedding band can conduct a current and burn your finger today MRI equipment is very fast and potentially dangerous due to higher magnetic fields and gradients.

By anon18198 — On Sep 17, 2008

I'm a radiologist from slovakia

reply to anon4919: because of lot of air in the lung parenchyma and breach motion of lungs the MRI is not dg procedure of choice for dg lung diseases..for mediastinum {heart and vessels around} it's OK but lung parenchyma is thin CT of former HRCT..

reply to anon1281: there are MRI with small magnetic fields {like 0,25 or 0,5 T} which are used mostly in sport medicine or private centers and there is possible to scan only some parts of the body..ask about that in such center..so no need for certain body parts to scanned by large MR..but with less T the resolution tedns to be worse

reply to anon112: fMRI is functional MRI now widely used but neurology to diagnose which part of e.g. brain is responsible for something..they use also contrast but they compare where the contrast {in which part of brain for example} is more metabolized by stimulation in some circumstances..google and U'll find many interesting thing about this rather new method..

By anon11159 — On Apr 09, 2008

I just had an MRI of my right knee done. The images came out kind of blurry (according to the tech) and it's probably because I couldn't keep my leg completely still during the scans. After the MRI was done and I got back to work I realized that I remembered that I had put a safety pin on my blouse (above my chest and below my neck) in the morning and I had it on during he MRI. Would this have caused the blurred images? Would it cause any other problems?

By anon7855 — On Feb 03, 2008

I work at an MRI center. There are many metal objects that can safely go into an MRI scanner. The issue is what kind of metal is it.

If it is attracted to a magnet, it should not even go into the room, much less into the scanner. Items that are real gold or real silver are not attracted to magnets, therefore safe to be in the room. (Like your wedding ring.) Also, implants such as knee implants, hip implants, staples and many other surgically implanted items often can be safely entered into the magnetic field. Since the advent of MRI and it being used so much, most surgical implants are of titanium, and not a problem. NO implants are put into the machine without documentation that the implant has been tested(endlessly and carefully in thorough research) that it is safe in a particular strength machine. Another consideration is that there are different 'strengths' (called 'Tesla') of machines. And a 3T machine is exponentially stronger than a 1.5T (which is common).

Bottom line - don't try to figure it out yourself. If you have anything that you weren't born with in or around your body, tell the technologist performing your scan before going into the room!!! They are responsible for your being safe. They have endless books and studies they can reference to know if an item is safe to be in the scanner room or not. Consider all the kinds of implants people can have now; stents, portacaths, staples, pins and rods, joint replacements, plates, etc, etc. If you tell the tech everything in or around your body, trust me, they will not Let you enter the room unsafely.

That said, you may have something like a 'safe to go into the room' pin in your leg, but they can't do your scan. That's because while the pin in your leg is safe to be in the machine, if you're getting a scan of the same part of the body where the metal is, it will distort the imaging, making it undiagnostic. (unable to give you information about the injury or reason you were scanned.) The metal distorts the imaging/picture.

Your safety is in the hands of you and your technologist. You - to let them know about anything on you that you weren't born with; and them - to make sure they don't put anything unsafe into the machine. In the 19 years I've worked in MRI - the only errors were made by people not letting the techs know about something. Never an error of a tech putting something into the machine that should not be there.

By anon4919 — On Nov 06, 2007

I was told MRI isn't recommended to check the lungs----I would appreciate your input on this. Thank You.

By anon4046 — On Sep 30, 2007

for knee MRIs you'll go in up to your chin, but your head will be out of the machine. it's really not that bad.

By anon1281 — On May 23, 2007

My daughter is to have a MRI scan on her knee and is extremely clastrophobic.If its is just her knee would she still have to go through that tunnel totally or would they just scan her knee?

By Dayton — On May 01, 2007

MRI procedures aren't like surgery, so the staples can't be ripped out of you. Though I don't know, I'd predict that the doctors intentionally used staples that wouldn't cause problems in an MRI. As for the wedding ring, I'm guessing that since it's probably not made out of magnetic material, it won't have a huge effect on the results of the MRI either.

If I were you, I'd trust the MRI technician.

Anyone else have any expertise in this area?

By loribeaule1 — On May 01, 2007

hello, my name is lori and i am scheduled for an mri on the 18 of this month and i know from having done this before that you are suppose to take off all jewlery and when i called the mri department and told them i can not take off my wedding ring and i asked then if i had to cut it off in order to have the test and she told me no it is OK i could leave it on.is that true or due i have it cut off? won't it mess up the machine? also i had gastric by-pass 1yr. ago and surgical staples are still in me and they will be there for life what about them? will the machine rip them out of me? please find out for me .it is very important that i find out right away. thank you very much. lori

By anon112 — On Apr 14, 2007

What is the difference between an MRI and fMRI?

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