Magnetic resonance imaging


Magnetic resonance imaging (MRI) is a unique and versatile medical imaging diagnostic tool. Using MRI, physicians obtain highly refined images of the body's interior. Strong magnetic fields and pulses of radio waves manipulate the body's natural magnetic, producing images not possible with other diagnostic imaging methods. MRI is particularly useful for imaging the brain and spine, as well as the soft tissues of joints and the interior structure of bones. The entire body can be imaged using MRI, and the technology poses few known health risks.


MRI was developed in the 1980s. The latest additions to MRI technology are magnetic resonance angiography (MRA) and magnetic resonance spectroscopy (MRS). MRA studies blood flow, while MRS identifies the chemical composition of diseased tissue and produces color images of brain function. The many advantages of MRI include:

Physicians sometimes choose other imaging techniques, such as ultrasound scanning, because the MRI process is complex, time-consuming, and costly. The process requires large, expensive, and complicated equipment; a highly trained operator; and a physician specializing in radiology. Generally, MRI is prescribed only when serious symptoms or negative results from other tests indicate a need. In many cases, an alternative imaging procedure is more appropriate for the type of diagnosis needed. However, some diseases such as multiple sclerosis are best imaged by MRI.

Physicians may prescribe an MRI scan of different areas of the body.


Magnetic resonance imaging

MRI produces a map of hydrogen atoms distributed in the body. Hydrogen is the simplest element known, the most abundant in biological tissue, and one that can be magnetically polarized. It will align itself within a strong magnetic field, like the needle of a compass. The earth's magnetic field is not strong enough to polarize a person's hydrogen atoms, but the superconducting magnet of an MRI machine can do this. The strength of the earth's magnetic field is approximately 1 gauss. Typical field strength of an MRI unit, with a superconducting magnet, is 1,500 gauss, expressed as 1.5 kilogauss or 1.5 Tesla units. This comprises the "magnetic" part of MRI. There are also low field units with 0.5 Tesla strength, often with open MRI units.

Once a patient's hydrogen atoms have been aligned in the magnet, pulses of very specific radio wave frequencies jolt them out of alignment. The hydrogen atoms alternately absorb and emit radio wave energy, vibrating back and forth between their resting (polarized) state and their agitated (radio pulse) state. This comprises the "resonance" part of MRI. The patient does not detect this process.

The MRI equipment detects the duration, strength, and source location of the signals emitted by the atoms as they relax. This data is translated into an image on a television monitor. The amount of hydrogen in diseased tissue differs from the amount in healthy tissue of the same type, making MRI particularly effective at identifying tumors and other lesions. In some cases, chemical agents such as gadolinium can be injected to improve the contrast between healthy and diseased tissue.

A single MRI exposure produces a two-dimensional image of a slice through the entire target area. A series of these image slices closely spaced (usually less than half an inch [1.25 cm]) provides a virtual three-dimensional view of the area.

Magnetic resonance spectroscopy

Magnetic resonance spectroscopy (MRS) is different from MRI because MRS uses a continuous band of radio wave frequencies to excite hydrogen atoms in a variety of chemical compounds other than water. These compounds absorb and emit radio energy at characteristic frequencies, or spectra, that can be used to identify them. Generally, a color image is created by assigning a hue to each distinctive spectral emission. This comprises the "spectroscopy" part of MRS. MRS is still experimental, and is available in only a few research centers.

Physicians mainly use MRS to study the brain and disorders such as epilepsy, Alzheimer's disease, brain tumors, and the effects of drugs on brain growth and metabolism. The technique is also useful in evaluating metabolic disorders of the muscles and nervous system.

Magnetic resonance angiography

Magnetic resonance angiography (MRA) is a variation on standard MRI. MRA, like other types of angiography, looks specifically at blood flow within the vascular system, without the injection of contrast agents (dye) or radioactive tracers. Standard MRI cannot detect blood flow, but MRA uses specific radio pulse sequences to capture usable signals. The technique is generally used in combination with MRI to obtain images that show both the structure of blood vessels and flow within the brain and head in cases of stroke, suspected blood clot, or aneurysm. In general, MRA is performed without contrast when examining the brain. Intravenous contrast is usually administered when other blood vessels, such as those in the neck, chest, or abdomen are studied.


Regardless of the type of MRI planned, or area of the body targeted, the procedure involved is basically the same, and occurs in a special MRI suite. The patient lies back on a narrow table and is made as comfortable as possible. Transmitters are positioned on the body and the cushioned table that the patient is lying on moves into a long tube that houses the magnet. The tube is the length of an average adult lying down, and the tube is narrow and open at both ends. Once the area to be examined has been properly positioned, a radio pulse is applied. Then a two-dimensional image corresponding to one slice through the area is made. The table then moves a fraction of an inch and the next image is made, and so on. Each image exposure takes several seconds, and the entire exam lasts 30–90 minutes. During this time, the patient is not allowed to move. Movement during the scan results in an unclear image.

Depending on the area to be imaged, the radio-wave transmitters are positioned in different locations.

Additional probes will monitor such vital signs as pulse and respiration.

The process is very noisy and confining. The patient hears a thumping sound for the duration of the procedure. To increase comfort, music supplied via earphones is often provided. Some patients become anxious, or they may panic because they are inside a small, enclosed tube. This is why vital signs are monitored, and the patient and medical team communicate with each other. If a patient has claustrophobia, the physician may prescribe an anti-anxiety drug prior to the procedure. If the chest or abdomen is to be imaged, the patient is asked to hold his or her breath for each exposure. Other instructions may be given as needed.

In many cases, the entire examination will be performed by an MRI operator who is not a physician. However, the supervising radiologist should be available to consult as necessary during the exam, and will view and interpret the results at a later time.

Open MRI units

Many adult patients and, especially children, become extremely claustrophobic when placed inside the confines of a full strength (1.5 Tesla) superconducting magnet. This problem is often severe enough to prevent them from having an MRI scan. In an alternative design, the magnet is comprised of two opposed halves with a large space in between. These units are known as open MRI machines. The advantage is that they can be used for patients who are claustrophobic. The disadvantage is that the field strength of the magnets is lower (usually 0.2–0.5 Tesla) than with standard full-strength machines. Lower strength magnetic fields require more time for image acquisition, increasing the risk of image problems because patients may have difficulty remaining still for longer periods of time.


In some cases (such as for MRI brain scanning or MRA), a chemical designed to increase image contrast may be given by the radiologist immediately before the exam. If a patient suffers from anxiety or claustrophobia, drugs may be given to help the patient relax.

The patient must remove all metal objects (i.e., watches, jewelry, eyeglasses, hair clips). Any magnetized objects, such as credit and bank machine cards or audio tapes, should be kept far away from the MRI equipment because they can be erased. The patient cannnot bring a wallet or keys into the MRI machine. He or she may be asked to wear clothing without metal snaps, buckles, or zippers, unless a medical gown is provided. The patient may also be asked to remove any hair spray, hair gel, or cosmetics that could interfere with the scan.

Side effects

The potential side effects of magnetic and electric fields on human health remain a source of debate. In particular, the possible effects on an unborn baby are not well known. Any woman who is, or may be, pregnant should carefully discuss this issue with her physician and radiologist before undergoing a scan.

Chemical agents may be injected to improve the image or allow for the imaging of blood or other fluid flow during MRA. In rare cases, patients may be allergic to or intolerant of these agents, and should not receive them. If chemical agents are to be used, patients should discuss any concerns they have with their physician and radiologist.

As in other medical imaging techniques, obesity greatly interferes with the quality of MRI.


No aftercare is necessary, unless the patient received medication or had a reaction to a contrast agent. Normally, patients can return to their daily activities immediately. If the exam reveals a serious condition that requires more testing or treatment, appropriate information and counseling will be needed.


MRI scanning should not be used when there is the potential for an interaction between the strong MRI magnetic field and metal objects that might be imbedded in a patient's body. The force of magnetic attraction on certain types of metal objects (including surgical steel and clips used to pinch off blood vessels) could move them within the body and cause serious injury. The movement would occur when the patient is placed into and out of the magnetic field. Metal may be imbedded in a person's body for several reasons:

Normal results

A normal MRI, MRA, or MRS result is one that shows that the patient's physical condition falls within the normal range for the target area scanned.

Generally, MRI is prescribed only when serious symptoms or negative results from other tests indicate a need. There often exists strong evidence of a condition that the scan is designed to detect and assess. Thus, the results will often be abnormal, confirming the earlier diagnosis. At that point, further testing and appropriate medical treatment are needed. For example, if the MRI indicates the presence of a brain tumor, an MRS may be prescribed to determine the type of tumor so that aggressive treatment can begin immediately without the need for a surgical biopsy.



Haaga, John R., et al., eds. Computed Tomography and Magnetic Resonance Imaging of the Whole Body. St. Louis, MO: Mosby, 1994.

Hornak, Ph.D., P. Joseph. The Basics of MRI.

Zaret, Barry L., et al., eds. The Patient's Guide to Medical Tests. Boston: Houghton Mifflin Company, 1997.


Jung, H. "Discrimination of Metastatic from Acute Osteoporotic Compression Spinal Fractures with MR Imaging." Radiographics 179 (January/February 2003).

Kevles, Bettyann "Body Imaging." Newsweek Extra Millennium Issue (Winter 97/98): 74–6.


American College of Radiology. 1891 Preston White Dr., Reston, VA 22091. (703) 648-8900. .

American Society of Radiologic Technologists. 15000 Central Ave. SE, Albuquerque, NM 87123-3917. (505) 298-4500. .

Center for Devices and Radiological Health. United States Food and Drug Administration. 1901 Chapman Ave., Rockville, MD 20857. (301) 443-4109. .


Smith, Steve. "Brief Introduction to FMRI." FMRIB. 1998. .

Stephen John Hage, AAAS, RT-R, FAHRA
Lee A. Shratter, M.D.

Also read article about Magnetic Resonance Imaging from Wikipedia

User Contributions:

leisha dishmon
The article was very informative; however, I would beg to differ on the statement the patient does not feel the layers of scanning. I had a brain MRI today and a spinal MRI today in hopes of diagnosing seizure symptoms and leg pain and numbness. When the actual, "what I call slicing" began, I could feel it. Not painful at all, it was like a wave inside my skull and back. The feeling was not the vibration of the machine. It was very distinguishable. It was an interesting experience. I did feel discomfort in my left eye and sinus cavities as it scanned in those areas. Also, in the past I have had a c-section and a hysterectomy and I could actually feel warmth in the area where the internal staples are. It has been three hours since my scans and I must say, my head feels a little fuzzy. Otherwise, it was a very unique experience.

Just thought I would share my experience with you.

leisha dishmon
nice nice.,it is a very useful information thanks a lot.,
dr pooja
your article is sufficent enough to understd about mri.but sir i want to know the procedure,and other facts about mri related to animals.wht r the use nside effect of mri in pls kindly send me related information as soon as possible.its very urgent.i m keenly waitng for ur reply sir.i m doind my from mhow veterinary college.m.p(india)
dr pooja
your article is sufficent enough to understd about mri.but sir i want to know the procedure,and other facts about mri related to animals.wht r the use nside effect of mri in pls kindly send me related information as soon as possible.its very urgent.i m keenly waitng for ur reply sir.i m doind my from mhow veterinary college.m.p(india)
Just came home from a non-contrast brain MRI. I too had the sensation of my brain being sectioned ..although not painful. I felt the procedure kind of 'shook up' my brain and was left with a dull headache and tenderness espcially around the left side...which was the are of focus. I also felt a bit dizzy afterwards.
Your article is infomative and useful to me. I will undergo for MRI next month but I'm worry about the effect of MRI to my stenting. I had my angioplasty two years ago. Some of my friends told me, MRI will cause the stent to move and will triger a stroke. Is it true? Please if you could clarify me on this. Thank you.
i had a MRI last week, and i was quite nervous, even tho i had my partner there with me holding onto my foot, the machine was not as loud as they were making out it would be.. thats what mainly worried me, it was a very strange experience, i could actually feel this machine scan right through me, in my head, like a sharp shooting pain in parts of my head very short moments of it, i dont care what anyone thinks i could really feel it! no other pains anywhere else, towards the end i started moving my face to much and they had do part of the scan again, then after 15 mins of that i told them to stop and that what pics they have got will have to do. as the lady told me 5 mins, i started speaking up telling her she lied to me and to stop , haha my partner told me to stop being silly and get on with it, then they wanted me to have some injection at the end, i said nup , no thanks, picked the results up the next day, cant really understand what is says, few strange things on here, but the comment at the end states. normal mri and mrv
Excellent article however, there are a couple of things I have to disagree with. I just had an MRI (without contrast) of my foot this morning. Every time the machine went into another cycle and started up, I felt tingling in my foot and sometimes in other parts of my body like my hands. Also, when the test was finished, I felt somewhat nauseous and had a mild headache which has not subsided ... I felt fine before the test started.
Thank you for this article. I was hoping to find informaion about pain during an MRI. I have been suffering from severe muscle breakdown in my quads, tremors/spasms throughout the body, speech and thinking issues. I went and had a brain mri. It put me through so much pain in my leg. I don't know why and so far can't find anything on the net. I know MRIs aren't normally painful, I have had others done do to cancer. This one made both of my feet go numb and then my right leg was in extreme pain. I only hope something shows as to why.
great article, but I too have had an open MRI of my brain neck and spine, it took 2 hours lying completely still and left me feeling like I had just woken up after a night on the tiles. I was not right for the following 3 days and was very emotional and snappy with it. I also felt a strong pulling in my right side during the scan too. on a good note I was allowed to lay on my left side for the scan not flat on my back!
Kim lee
I just had a brain mra. Over the phone I told the girl I had 11stents. This morning as soon as I got there I gave the girl at the desk my stent cards , she didn't look at them. I went in the back by the locker with a nurse. I showed her my stent cards She looked at one & said ok. When I went in the room there were two nurses , I think & a man , none of them were interested in looking at my cards. They said all stents are safe. I said the girl on the phone told me I was getting the lowest dose machine. They all 3 said yes. Good thing I'm experienced. LOL. Within one minute of laying down, which by the way I've had plenty of mri's with my stents. All of a sudden my chest feels like heat. I thought it was weird. Then it was getting hotter It felt like a hot hot heating pad real hot but inside my chest & chest pain Like my stents were getting pulled out of my body. I'm very thin,85lbs. Well,10hrs later I still feel the same way. When I spoke with Zwanger & Pesiri. They said no way it's from MRA. I found out they gave me the strongest machine & I'm 100% positive this is from the MRA. Looks like I'm going to be hospitalized now. Greaat
I would just like to add to the thread of what is felt during an MRI. I had an MRI of the liver region friday, imaging with and withoug Gadolinium. I very clearly felt a tugging, pulling, slicing sensation in the right side during the noisy part of the session. Not painful but distinct. It should be noted that I have never had pain in my liver or that area. After the MRI I went about my day as usual, but in the evening and very pronounced yesterday saturday. Liver area and ribs felt tender and 'tight'. Today sunday it is somewhat better. I assume this sensation was due to the strong magnetic field of the MRI and the nerves reacting to the pulsations. An indication by the staff that this kind of sensation might happen and if it is normal, would be helpful. Though not a worrier I am ofcourse wondering what the MRI might have affected or activated in that region of the body.
I had an MRI a few days ago for the head, cervical and thoracic spine(with and without Gadolinium) and the duration was 3 hours. I have had several MRIs but this time I had strong spasms in my left leg. This is the first time I had a series of multiple leg spasms in the leg that I don't have spasms. I read this article to learn if that type of reaction to an MRI was normal. The tech saw the leg spasms as my foot moved' and asked if I take meds for spasms and I do not. This was the first time when it was fairly continuous in the second and third hour. The tech had never conducted a 3 hour MRI so I do not know if this reaction was normal.
I had a MRI for the first time today of my abdomen... Test went well, I kept my eyes closed, and one thing that was a little odd to me, was I felt like my body was slowly lifting off of the bed I was laying on, but it felt lightweight... Like it was pulling on my spirit.. A few times I had to open my eyes to make sure I was not floating.. This sensation only happened a few times... Wasn't scary, but wondered if it was from the magnetic pull... The test was 4 hours ago, and now i find my pelvic/butt bones are aching... It is aching as I sit, or stand... Anyone else ever experience this?
just got out of an MRI for an ankle injury. it makes sense to me that there should be some sensation but wow i did not expect the pain to be so intense for a half hour scan. I could feel the effects of the field immediately like my nervous system was aware of the disturbance but didn't know how to explain it to my brain. i could feel intermittent tingling and twinges and a gradual increase in heat and pressure on the tenderest ligaments in the joint until the pain became almost unbearable. the ankle position was a factor but it did not explain the deep sensation in my ankle like it was about to explode or be torn apart inside out. If I had to describe what polarizing hydrogen atoms in your body felt like this would be it. it sucked huge. this article sure sounds like the right amount of diluted information mixed with that smidge of medical propaganda.
I had a three and a half hour MRI from head to toe with contrast. I have had a spinal fusion at L3-4,4-5,S1. With a bone simulator implanted for 10 months. My question is this. Is it o.k to have an MRI with all the metal in me from the fusion as well as the internal bone simulator. Due to the internal bone stem causing me severe health problems after it moved from its location and got lodged in between my spine and screws I had to have a judge force the doctor and insurance company to remove and pay for it. The st emulator was from the IED corp implanted Nov, 06,2003. The bone stem was taken out with the wires and clamps left intact. Nine years later I am seeing an oncologist next week for tumors that have grown all over the trunk of my body especially on the rt and lf sides of my lower back and two very large growths on my spine(radiologist say neurofibromatosis). Not sure how they differ from all the other ones. Anyways have you ever heard of such a thing and could having multiple MRI,CT and Xrays have anything to due with it thank you
Does an MRI have any effect on teeth that have a metal crown over root canal roots? After my MRI on my head, I had two small lumps about the size of a medium sized gum drop, one at the base of this tooth in the jaw and another on top of my skull. Both formed within a day of having the MRI. Doctors and the Dentist doubt that the MRI caused either of them. I hav e to wonder since both came on the next day. The jaw bone one swelled and had moderate pain but did go away. The skull top one had no pain but is still there some six months later.
I just had an MRI of my lumbar spine this morning. The whole procedure took about 20minutes which felt like forever. the noise was unbearable, moreso because of the different tones. I felt a warm sensation on my right flank and the heat increased towards the end of the test. The technician said it was normal. I felt so tired after the test and needed a few minutes to rest before leaving. Then came the headache...I wish the whole process had been explained to me before. Proper earplugs would also do a better job than cotton wool balls given to me.
Richard Anderson
I just had an mri today stents from 3 years ago. I provided all the stent information to the doctor and as soon as the test started I could feel burning in chest. I notified attendant who told me if anything was going to happen it already would have. I still hours after can feel pain in my chest. I am getting kind of worried if she was correct or should I go see a cardiologist now?
my head burned after my am sitting with ice on my head for hours.I had the M.R.I. without contrast and it was of my brain and spine for a car accident I had 8 day's ago.I have high histamines, Dermatagraphism so maybe this was it but I definetly feel like I have a badly sunburned head and my scalp is red all through out.Hope I FEEL better tomorrow.
Just completed a C Spine MRI. My last 3 MRI's I've had the same experience so it's not positioning, anxiety/panic or any other excuse. There really are effects with MRI's that people can feel. On the last picture process I had them stop due to the sensations I was feeling and their intensity and was unsure how severe it was going to get. Exactly as others have described, I had a pulling sensation in my head, odd burning sensation behind my left eye & almost felt as if my eyes were moving uncontrollably (kept my eyes closed). Took me several minutes to get the fuzziness out of my head & get the sensation from my eye to stop and then I continued with the test. Post test, I'm very shaky with dull headache, slight nausea. I am completely convinced that the magnet was strong enough to cause these sensations. (I have worked in the medical field for 19 years). Neck muscles are also very tight.
I had a two hour MRI on my brain for MS. I am in a study so the machine is stronger than the average. During the last three scans my brain started to burn. It continued to build and get worse until the tests stopped. It was very scary. it is the second time it has happened and i am having to continue to have MRIs on the study i am on. Has anyone else had this experience???
I just had a MRI on my ankle, and I could feel like layers going through my ankle at different points, anyway I had pain in the areas that was bothering me, my question is, is this normal or does it mean I have factures or torn ligaments? Just hate waiting for results
kimberly faria
im 26 years old how can I tell if my shunt is plastic or medal I need to no because my doctor can't do the mri without knowing if it is plastic or medal help me find out please I have this shunt since newborn
My question it possible to have 18 Mri's in 1 month? I realize this may sound like a stupid question but I need an answer and cannot find one anywhere on this topic.
post torture
I had an MRI yesterday of sinuses and neck and shortly into it, a pressure point started on the back of my head. By the end of the hour I felt like was being tortured. Imagine a sharp stone in your shoe and being made to stand on it for an hour- that was what was in the back of my head. I was nearly weeping from the pain and I know I didn't hold still. That bulb thing they give you to call the technician is useless- unless they just want to hear you scream. I asked if I could take a break before she injected the contrast and the technician said no. No one told me to empty my pockets. My car keys wound up on the side wall of the machine. Technician tossed them aside and casually said, well, I hope they still work. Ha ha. She left my watch on too. It was ok but the time was wrong when I got out. I'm still having flashbacks. I have migraines, I have broken ribs in the past, once walked a couple of miles with a sprained ankle- I'm no stranger to pain and this was one of the worst experiences I have ever had. I don't know why more isn't said about the pain from having to be in one position for so long.
Nancy clark
A metal clip left during a colonoscopy in large intestine. Started feeling worse took CT which showed a metallic structure. It was ignored and Dr. still let me go into a MRI. I am 5’1 and 98 pounds and I looked like I was pregnant with 4. Lasted for about a week. Has anyone had side effects. I have had so many. And still do. But the doctor had been stating otherwise until I started looking things up and I am the one that found it. He finally admitted 2 weeks ago. I haven't done a thing. I have been so sick. Hair loss, 21 times bathroom. depression, Migraine, bumps on Skin, Harder to see and Hear. Nerve in face hurts, not sexually active, stomach hurts so much, arthritis. hot flashes, stomach has weird tingle sensation that wakes me up in the morning. fingers, toes and heels tingle or go numb, tired bruising, emotional, fingernails are splitting, stool is always changing, fistulas, hemorrhoids, fissures. HOMEBOUND.
Wendy Ball
I had an MRI in my knee today and I couldfeel odd sensations from my ankle to the top of my leg. I had a sandbag put across my foot prior to the start of the scan in case of any movement I was told. It was a strange sensation but not at all painful. However afterwards, my eyes didn't focus properly for about ten mins after.
constance cutsumbis
Yesterday had MRI on knee since procedure I am experiencing sharp little pains in left breast area. In 1908 I had one stent paced. Would this be causing my sharp little pains ?
maryanna hart
I had a MRI for left knee pain today.. and during the procedure it felt like the back of my leg in the knee area was being pulled out.. like something was trying to pull my kneecap thru the back of my leg... it was horrible. I made it thru with meditation.. and right at the end when I couldnt take anymore.. I jumped.. and it was then over. I couldnt stand correctly... was a bit off balance.. now that spot hurts with a dull ache and it feels hot. and I just called radiology, they said call my Dr. office is closed, I called ER.. they said it shouldnt be anything to worry about. ?? I'm lost.

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