If you have claustrophobia or anxiety, you may want to ask your doctor for a mild sedative prior to the exam. Magnetic resonance imaging MRI is a noninvasive test doctors use to diagnose medical conditions. MRI uses a powerful magnetic field, radiofrequency pulses, and a computer to produce detailed pictures of internal body structures.
MRI does not use radiation x-rays. You will need to change into a hospital gown. This is to prevent artifacts appearing on the final images and to comply with safety regulations related to the strong magnetic field. Guidelines about eating and drinking before an MRI vary between specific exams and facilities. Take food and medications as usual unless your doctor tells you otherwise.
Some MRI exams use an injection of contrast material. The doctor may ask if you have asthma or allergies to contrast material, drugs, food, or the environment. MRI exams commonly use a contrast material called gadolinium. Doctors can use gadolinium in patients who are allergic to iodine contrast. A patient is much less likely to be allergic to gadolinium than to iodine contrast.
However, even if the patient has a known allergy to gadolinium, it may be possible to use it after appropriate pre-medication. Tell the technologist or radiologist if you have any serious health problems or recent surgeries. Some conditions, such as severe kidney disease, may mean that you cannot safely receive gadolinium. You may need a blood test to confirm your kidneys are functioning normally.
Women should always tell their doctor and technologist if they are pregnant. MRI has been used since the s with no reports of any ill effects on pregnant women or their unborn babies. However, the baby will be in a strong magnetic field.
Therefore, pregnant women should not have an MRI in the first trimester unless the benefit of the exam clearly outweighs any potential risks. Pregnant women should not receive gadolinium contrast unless absolutely necessary.
If you have claustrophobia fear of enclosed spaces or anxiety, ask your doctor to prescribe a mild sedative prior to the date of your exam. Leave all jewelry and other accessories at home or remove them prior to the MRI scan. Metal and electronic items are not allowed in the exam room.
They can interfere with the magnetic field of the MRI unit, cause burns, or become harmful projectiles. These items include:. In most cases, an MRI exam is safe for patients with metal implants, except for a few types. People with the following implants may not be scanned and should not enter the MRI scanning area without first being evaluated for safety:.
Tell the technologist if you have medical or electronic devices in your body. These devices may interfere with the exam or pose a risk. Many implanted devices will have a pamphlet explaining the MRI risks for that device. If you have the pamphlet, bring it to the attention of the scheduler before the exam. MRI cannot be performed without confirmation and documentation of the type of implant and MRI compatibility.
You should also bring any pamphlet to your exam in case the radiologist or technologist has any questions. If there is any question, an x-ray can detect and identify any metal objects. Metal objects used in orthopedic surgery generally pose no risk during MRI.
However, a recently placed artificial joint may require the use of a different imaging exam. Tell the technologist or radiologist about any shrapnel, bullets, or other metal that may be in your body. Foreign bodies near and especially lodged in the eyes are very important because they may move or heat up during the scan and cause blindness. Dyes used in tattoos may contain iron and could heat up during an MRI scan.
This is rare. The magnetic field will usually not affect tooth fillings, braces, eyeshadows, and other cosmetics. However, these items may distort images of the facial area or brain. Tell the radiologist about them.
Infants and young children often require sedation or anesthesia to complete an MRI exam without moving. This depends on the child's age, intellectual development, and the type of exam. Sedation can be provided at many facilities. A specialist in pediatric sedation or anesthesia should be available during the exam for your child's safety.
You will be told how to prepare your child. Some facilities may have personnel who work with children to help avoid the need for sedation or anesthesia. They may prepare children by showing them a model MRI scanner and playing the noises they might hear during the exam. They also answer any questions and explain the procedure to relieve anxiety. Some facilities also provide goggles or headsets so the child can watch a movie during the exam.
This helps the child stay still and allows for good quality images. The MRI is controlled from a nearby room. You will be closely observed throughout the procedure. A series of scans are taken with a brief pause between each. You may hear different noises as different scans are taken. It's normal for the noise to be very loud. You need to remain still when the scan is being taken.
People are typically in the scanner from 30 to 50 minutes, depending on the images to be taken. A complex examination can take longer. If you are concerned about being in the scanner for this length of time, talk to your physician and the technologist. They can help you with some tips for staying comfortable. If you need to be removed from the scanner, this can be done very quickly. The ends of the scanner are always open. After your exam, the images will be reviewed by your radiologist. He or she will send a report to the health care provider who ordered the test.
Ask your health care provider any questions you have about your MRI. A cardiac MRI provides still or moving pictures of how the blood is flowing through the heart. Vivien Williams: One out of four, that's how many people will die of a heart related problem. Doctors at Mayo Clinic are trying to improve those statistics.
They're using MRI s to look inside the heart to find disease and tailor treatment to keep people healthier longer. Brian Shapiro, M. Vivien Williams: Dr. Brian Shapiro uses MRI to look for abnormalities in the heart. So, swelling of the heart is a very common thing in heart attacks, and infections, and things like that. Shapiro how well the heart pumps, where irregular heart beats originate, the location of blood clots, artery blockages, scar tissue, or even tumors.
Because MRI allows doctors to see more detail of the heart, they can make more accurate diagnoses, and therefore tailor treatment for patients. Vivien Williams: Images that tell Dr. Shapiro if a patient will recover, if there's permanent damage, and what treatments might be best. Information from inside the heart that can help Dr. Shapiro and his colleagues better help their patients. Shapiro says while MRI can show lots of information about the heart, it does not replace other tests such as stress tests or echo cardiograms.
It's another option for looking inside the heart. In most other cases, it is usually not necessary to avoid food or drink prior to the scan.
However, be advised by your doctor. Claustrophobia — tell your doctor if you experience claustrophobia. Some patients find the confined space within the MRI scan unsettling. The doctor may offer you medication to help you relax during the procedure. Children — often children are given anti-anxiety medication prior to the procedure to help them relax.
Talk to your doctor if you have any concerns about this. MRI scan procedure Generally, an MRI involves the following: You will be asked to remove all metal objects, including wristwatches, keys and jewellery. These items must be left outside the scan room. In most cases, you are asked to undress and put on a cotton gown. The table then slides into the cylinder.
An intercom inside the MRI scanner allows you to talk with the radiography staff. It is important to lie very still. Movement will blur or distort the pictures. While it is in operation, the MRI scanner makes noises such as knocks, loud bangs and clicks. You may be offered earplugs. In some cases, you can listen to music through headphones if you prefer.
The scanned area of your body may feel a little warm. The scan may take up to an hour, depending on the nature of the investigation. Immediately after the MRI You may be asked to wait while the radiographer checks the quality of the pictures. This difference means they require a huge amount of electricity, making it prohibitively expensive to operate above a 0. Permanent magnets have a constant magnetic field, but they're so heavy that it would be difficult to construct one that could sustain a large magnetic field.
There are also three gradient magnets inside the MRI machine. These magnets are much lower strength compared to the main magnetic field; they may range in strength from gauss to gauss. While the main magnet creates an intense, stable magnetic field around the patient, the gradient magnets create a variable field, which allows different parts of the body to be scanned.
Another part of the MRI system is a set of coils that transmit radiofrequency waves into the patient's body. There are different coils for different parts of the body: knees, shoulders, wrists, heads, necks and so on. These coils usually conform to the contour of the body part being imaged, or at least reside very close to it during the exam.
Other parts of the machine include a very powerful computer system and a patient table, which slides the patient into the bore. Whether the patient goes in head or feet first is determined by what part of the body needs examining. Once the body part to be scanned is in the exact center, or isocenter , of the magnetic field, the scan can begin.
MRI machines are evolving so that they're more patient-friendly. For example, many claustrophobic people simply can't stand the cramped confines, and the bore may not accommodate obese people.
There are more open scanners, which allow for greater space, but these machines have weaker magnetic fields, meaning it may be easier to miss abnormal tissue. Very small scanners for imaging specific body parts are also being developed.
Other advancements are being made in the field of MRI. Functional MRI fMRI , for example, creates brain maps of nerve cell activity second by second and is helping researchers better understand how the brain works.
Magnetic resonance angiography MRA creates images of flowing blood, arteries and veins in virtually any part of the body. When patients slide into an MRI machine, they take with them the billions of atoms that make up the human body. For the purposes of an MRI scan, we're only concerned with the hydrogen atom, which is abundant since the body is mostly made up of water and fat. These atoms are randomly spinning, or precessing , on their axis, like a child's top.
All of the atoms are going in various directions, but when placed in a magnetic field, the atoms line up in the direction of the field. These hydrogen atoms have a strong magnetic moment , which means that in a magnetic field, they line up in the direction of the field. Since the magnetic field runs straight down the center of the machine, the hydrogen protons line up so that they're pointing to either the patient's feet or the head.
About half go each way, so that the vast majority of the protons cancel each other out -- that is, for each atom lined up toward the feet, one is lined up toward the head. Only a couple of protons out of every million aren't canceled out. This doesn't sound like much, but the sheer number of hydrogen atoms in the body is enough to create extremely detailed images.
It's these unmatched atoms that we're concerned with now. The system directs the pulse toward the area of the body we want to examine. When the pulse is applied, the unmatched protons absorb the energy and spin again in a different direction. This is the "resonance" part of MRI. The RF pulse forces them to spin at a particular frequency, in a particular direction. The specific frequency of resonance is called the Larmour frequency and is calculated based on the particular tissue being imaged and the strength of the main magnetic field.
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