FAQs About Magnetic Resonance Imaging (MRI)

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Will the MRI hurt?

No – the MRI itself should cause no pain, it only requires that the patient remain still during the examination. For some patients, keeping still may be slightly uncomfortable. Sometimes patients may feel warmth in the area being imaged – this is normal. However, if this warmth becomes irritating or excessive, the patient should notify the imaging technologist as soon as possible.

MRI exams which require the patient to receive Gadolinium contrast may cause slight, temporary discomfort while the intravenous needle is placed (see "Do I need an injection?").

How long will the MRI take?

Most MR centers offer a wide array of MRI exams. Depending on the type of exam you will receive, the length of the actual procedure will typically vary between 15 minutes and 45 minutes. More involved MRIs may take longer than 45 minutes.

Some MRIs require the patient to hold their breath several times. This helps to eliminate blurring from the images, which can be caused by breathing or other patient motion. Please discuss specific questions about the duration of your MRI with the MR technologist before your exam.

Why does the MRI machine make that knocking sound?

The tapping or knocking noise heard during the MRI is created when "gradient coils" are switched on and off to measure the MR signal reflecting from the patient's body. 

The gradient coil is one of several internal parts of the MR system that you can not see. The gradient coil is made up of loops of wire which are embedded in a hard plastic tube. During the scanning process, an electric current is switched on and off through the gradient coil every few milliseconds. Because the switching is so rapid, the wires vibrate within the hard plastic and cause the knocking sound.

This knocking is not harmful but the sound can be irritating to some patients. You will hear different knocking sounds during the MRI – this means that different types of "MR sequences" are being run to acquire different views and images of your body.

Why would I need to have an X-ray done before my MRI?

MRI involves the use of a strong magnetic field capable of pulling on many metal objects. Thus, for safety reasons, the MR staff must determine if you unknowingly have metal in your body. This includes small pieces of metal in your eyes, metal implants, prosthetic devices that may contain metal, surgical clips and/or other implanted objects that may be susceptible to the magnetic field. After asking you a few questions, the MR team will decide if an X-ray is necessary.

Will an MRI affect dental fillings?

No – an MRI will not cause fillings in your teeth (if in proper condition) to dislodge or come out. The metal in most fillings is not affected by the MR system's magnetic field. However, fillings may cause some distortion of the images if you are having a scan of your neck, brain or facial area.

Can I have an MRI if I have braces?

Patients with braces may receive an MRI. However, if you have braces and need an MRI of your brain or facial area, the MR system may have difficulty "tuning" to your body. The MR tuning process is similar to tuning a radio to a specific frequency or radio station. This tuning process can be "confused" if the patient has metal in his or her body, particularly if the metal is in the area being imaged. Unfortunately, there is no way to know in advance how much distortion from braces may result on MRIs of the head, face or upper neck.

Do I have to go all the way inside the MR scanner tunnel?

Yes – however, only the portion of the body that is being imaged must be positioned in the middle (end to end and side to side) of the MR system's tunnel or "all the way inside." For example, if a head study is being performed, the patients head must be positioned in the middle of the tunnel. For knee studies, the knee is positioned in the middle of the tunnel with the patients head facing the open end or possibly outside of the open end of the scanner (depending on the length of the magnet tunnel and the height of the patient).

So-called "Open MR" systems do not have a tunnel design and may be more comfortable for some patients. Most MR systems use the cylindrical tunnel design; however, recent versions of the cylindrical MR systems have tunnels that are shorter and more comfortable than systems designed and manufactured previously.

See 6 Ways to Stay Calm During MRI.

Is sedation or anesthesia available?

UC San Diego offers the latest in fast scanning and patient comfort techniques to reduce or eliminate claustrophobia and patient discomfort. However, sedation or pain medication is available if needed to complete exams. Please consult with your physician prior to your appointment for an appropriate prescription.

Do I need a referral (prescription) to receive an MRI?

Yes, your doctor must give you a referral (prescription) in order for you to receive an MRI.

Can I move while I'm in the MR tunnel?

You should not move when you are inside the tunnel or when you hear the knocking sound. For most MRIs, you may reposition your arms or scratch your face or body in between image acquisition (when the knocking has stopped). However, it is important that you refrain from moving the body part that's being imaged until the end of the exam.

Note: An MRI of the chest and abdomen may require the patient to hold their breath for a short period of time (e.g., 10 to 25 seconds). This eliminates blurring in the image caused by breathing or other patient motion.

Can I talk with anyone during the scan?

You may talk to the technologists or ask a question in between image acquisition. You will know when a picture is complete because the knocking and slight vibration will stop.

Can I bring a friend or a relative into the MR scan room with me?

Various MR centers may have different procedures regarding this question (depending upon the type, strength and external shielding of their magnet). All people entering the MR scan room should be checked for metal in or on their body.

This check may include the removal of:

  • Keys
  • Coins
  • Jewelry
  • Watches
  • Hairpins
  • Hairclips
  • Hearing aids
  • Wallets
  • Credit cards or ID cards with magnetic strips 

From a medical and safety standpoint, if your companion is checked and cleared to enter the MR scan room, he or she may safely accompany you for the exam. Typically your companion will be seated in a chair next to the MR scanner, or they may stand next to the patient table during your exam.

Will I need to get an injection?

Not everyone needs an injection for their MRI. When an injection is needed, a pharmaceutical contrast agent called Gadolinium is administered to the patient. This is only done when the radiologist and/or the referring physician have determined that it is necessary for diagnostic purposes.

Gadolinium contrast is used to make specific organs, blood vessels or tissue types "stand out" with more image contrast in the resulting picture. This highlights the structure of the specific organs or vessel to better show the presence of disease or injury.

The referring doctor provides the MR center with information about the patient's medical condition and the goal of the MRI procedure being ordered (e.g., to diagnose cause of intense back pain). The decision to use or not to use an injection of contrast (Gadolinium) is made based on this information and the body part being examined.

How is the Gadolinium injection given for an MRI?

If an MRI does require the use of a Gadolinium injection, a small needle connected to an intravenous line is usually inserted into the patient's arm or hand. A special saline solution is first dripped in to keep the vein from clotting. Then a contrast agent called Gadolinium is administered through the intravenous line (typically about two-thirds into the exam).

At the time of the injection, a patient may feel a cool sensation going up his or her arm. As with anything taken into the body, there is a very slight chance of an allergic reaction.

Can I breastfeed after an Gadolinium injection?

Yes. Only a tiny amount of the contrast agent gets into breast milk and the baby then absorbs only a small fraction of what they drink. Gadolinium is not a radioactive agent. The American Academy of Pediatrics states that Gadolinium is safe for breastfeeding mothers because the infant's dose is so small. We strongly recommend that you continue to breastfeed your baby after the scan, and not throw away any milk.

Can I have an MRI if I'm pregnant?

This question is difficult to answer with a simple "yes" or "no." MRI (magnetic resonance imaging) is considered a safe exam. However, conclusive information showing how safe MRI is for pregnant women and the fetus is not yet available. MR imaging is generally not performed on women in the first twelve weeks of pregnancy (first trimester).

Physicians typically do not perform MRI on pregnant women unless there are strong medical indications. Depending on the condition, there may be other exams available, such as ultrasound, to help diagnose a medical condition.

If there is a strong medical reason for an MRI, your physician may consult with a radiologist to determine if MRI is the best course of action before proceeding. An abbreviated MRI exam may be performed, to reduce the time in the magnetic field, based on the recommendation of the referring physician and radiologist. Please consult with your physician for more specific information.