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Johns Hopkins Medical Imaging

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Magnetic Resonance Imaging (MRI)

MRI uses high-powered magnets and radio waves to produce images of organs and structures inside the body. The MRI scanner is shaped like a building block with a very large hole in the middle where the patient lies on a table during the exam. The picture quality is at its best in the center of the magnet. This is why the part of your body that your doctor needs examined is always placed in the center. The information collected by the MRI scanner is sent to a computer and translated into images.

Learn more about MRI exams in the Johns Hopkins Health Library.

How do I prepare for a MRI exam?

EAT/DRINK: You may eat, drink and take medications as usual, unless your health care provider tells you otherwise.

CLOTHING: You must completely change into a patient gown and lock up all personal belongings. Please remove all piercings and leave all jewelry and valuables at home.

ALLERGY: Some MRI exams require IV contrast. If you have had an allergic reaction to contrast that required medical treatment, contact your ordering physician to obtain the recommended prescription for Prednisone 40mg by mouth 24, 12 and two hours prior to examination.

ANTI-ANXIETY MEDICATION: If you require anti-anxiety medication due to claustrophobia, contact your ordering physician for a prescription. You must bring the medication with you for your appointment. The MRI technologist will give you instructions for when to take your medication. Please note that you will need someone else to drive you home.

STRONG MAGNETIC ENVIRONMENT: Due to the strong magnetic field, you must inform your doctor prior to the appointment if you have any metal in your body. Detailed information will be needed, such as the type and location, to determine your eligibility for MRI. If you have metal within your body that was not disclosed prior to your appointment, your study might be delayed, rescheduled or canceled upon your arrival until further information can be obtained.

When you call to make an appointment, please let us know if you have any of the following:

  • You have a pacemaker or have had heart valves replaced
  • You have any type of implantable pump, such as an insulin pump
  • You have metal plates, pins, metal implants, surgical staples or aneurysm clips
  • You are pregnant or suspect you may be pregnant
  • You have ever had a bullet wound
  • You have ever worked with metal (for example, a metal grinder or welder)
  • You have metallic fragments anywhere in the body
  • You are not able to lie down for 30 to 60 minutes

What happens during a MRI exam?

  1. Your MRI exam takes places inside of a large tube-like structure, open on both ends. You must lie perfectly still for quality images.
  2. You will lie on a table that slides into the tunnel of the MRI machine. During the scanning process, a clicking noise will sound as the magnetic field is created and radio waves are sent from the scanner. Because the machine is very loud, you will be given earplugs that are required.

Learn more about what happens during an MRI exam.

What happens after a MRI exam?

There is typically no special type of care after an MRI.

If contrast dye is used during your procedure and you experience any side effects or reactions to the contrast, such as itching, swelling, rash or difficulty breathing after your appointment call your doctor right away. If you feel it is a life threatening emergency, call 911.

You may resume your normal diet and activities, unless your doctor advises you differently. Your doctor may give you additional or alternate instructions after the procedure depending on your particular situation.

What MRI exams are performed at Johns Hopkins Medical Imaging?