MRI is a method of producing extremely detailed pictures of body tissues and organs without the need for X-rays. The electromagnetic energy that is released when exposing a patient to radio frequency waves in a strong magnetic field is measured and analyzed to produce both two- and three-dimensional images that may be viewed on a computer monitor. This advanced imaging technique allows for the evaluation of some body structures that may not be as visible with other imaging methods.
Areas of Application
Benefits
- Images of the brain, spine, joints and soft tissue structures are clearer and more detailed than with other imaging methods.
- Contrast material is less likely to produce an allergic reaction than the iodine-based materials used for conventional X-rays and CT scans.
- Exposure to radiation is avoided.
- Detection of abnormalities that might be obscured by bone tissue with other imaging methods is achieved.
- New MRI systems can depict brain function, and in this way detect a stroke at a very early stage.
Risks
- The examination poses virtually no risk when appropriate guidelines are followed.
- Metal implants may be affected by the magnetic field. The procedure should be avoided in any patient with a pacemaker, implanted neurostimulator, certain types of metallic ear implants (cochlear implants) or metallic object within the eye socket. It should also be avoided if the patient has a port for delivering insulin or chemotherapy (however, many ports are detachable so patients can safely undergo MRI examinations). If you have an implant, please bring the implant identification card or letter from the physician who placed the implant.
- Although MRI is generally avoided in the first 12 weeks of pregnancy, pregnant patients should be informed that, to date, there has been no indication that the use of clinical MR imaging during pregnancy has produced deleterious effects. For more information, please see our Patient Safety Guidelines section and click the link to Pregnancy and MRI.
- Women who are breast-feeding should inform the radiologist and ask how to proceed. MRI poses no risk to milk or breast tissue, but if contrast dye (gadolinium) is required, the radiologist will discuss safety strategies. If necessary, they may pump breast milk before the exam for use until the gadolinium contrast material has cleared from the body.
About MRI Examinations
Q1. How does the procedure work?
MRI is a unique imaging method because, unlike the usual radiographs (x-rays), radioisotope studies and even CT scanning, it does not rely on ionizing radiation. Instead, radio waves are directed at protons, the nuclei of hydrogen atoms, in a strong magnetic field. The protons are first "excited" and then "relaxed," emitting radio signals, which can be computer-processed to form an image. In the body, protons are most abundant in the hydrogen atoms of water - the "H" of H2O - so that an MRI image depicts differences in the content and distribution of water in various tissues. With MRI, different types of tissue within the same body structure are clearly displayed in fine anatomic detail. In the spine, for instance, fatty tissue, cerebrospinal fluid and the intervertebral discs contain considerable water, more than is found in bone, cartilage and nerve tissue. MRI is well suited to detecting conditions that increase the amount of fluid, such as tumors, inflammation and infection. Even different types of tissue within the same organ, such as the gray and white matter of the brain, can easily be distinguished. Special imaging techniques are used to image various structures, such as arteries in the case of MR Angiography, or MRA.
Q2. How is the procedure performed?
The patient is placed on a special table and positioned inside the opening of the MRI unit. A typical exam consists of two to six imaging sequences, each taking two to 15 minutes. Each sequence provides a specific image orientation and a specified degree of image clarity or contrast. Depending on the type of exam being done, the total time needed can range from 20 to 60 minutes, not counting the time needed to change clothing, and answer questions. When contrast material is needed, a substance called gadolinium is given by IV injection during one of the imaging sequences. It highlights blood vessels and pathology, making them stand out from surrounding tissues. If you are having the shoulder, knee, or other specific joint imaged, direct injection of contrast into the joint may be required. The injection is performed either prior to, or about half-way through the exam (please see section on “MRI Arthrography” for details). The technologist leaves the room during the actual imaging process, but the patient can communicate with them at any time using an intercom. A friend/relative or, if a child is being examined, a parent may stay in the room. When the exam is completed you may be asked to wait to make sure that more images are not needed.
Have an upcoming MRI examination?
Q1. How do I prepare for my examination?
You will wear a lightweight medical gown for the exam.
The magnetic field used for MRI will pull on any iron containing object in the body, such as a heart pacemaker, artificial heart valve, aneurysm clip in the brain, vascular access port (most are MRI safe), metal plate, pins, screws or staples. If you have an implant, please bring the implant identification card or letter from the physician who placed the implant. You will be given a questionnaire to answer regarding these issues. The technologist should know about any such item and also whether you have ever had a bullet in your body, whether you ever worked with metals, or if you have had a joint replacement. If there is any question of metal fragments, especially in the eye, you may be asked to have an x-ray that will detect any such metal objects. In most cases, joint replacements, surgical staples, artificial heart valves, plates, pins and screws pose no risk during MRI if they have been in place for more than four to six weeks. Braces make it harder to properly adjust the MRI unit, but are safe. You will be asked to remove anything that might degrade the MRI images such as hairpins, jewelry, eyeglasses, hearing aids and any dental work that can be taken out. Some wigs contain metal and must be removed. Dyes used in tattoos and permanent eyeliner may contain metallic iron oxide and could heat up during MRI; however, this is rare.
You should report any drug allergies to the technologist
You can eat normally before the exam (unless told differently) and medications may be taken as usual.
Some patients will feel uncomfortably confined (claustrophobic) when enclosed in an MRI unit. If necessary, you can schedule your appointment with oral sedation which will be given fifteen to thirty minutes before your exam to help put you at ease. You will not be put to sleep, but merely relaxed. You will be asked to bring someone to drive you home if you receive a sedative. A young child should not eat or drink for about four hours if they will receive a sedative. Roughly one in twenty patients will require medication. Another option is to use an “open” MRI unit for some exams, or to be put completely asleep by an anesthesiologist in cases of severe claustrophobia.
Women should always inform the technologist and radiologist if there is any possibility that they are pregnant.
Q2. What will I experience during an MRI?
MRI causes no pain. You may notice a warm feeling in the area under examination; this is normal, but if it bothers you, inform the radiologist or technologist. If a contrast injection is needed, there may be discomfort at the injection site, and you may have a cool sensation at the site during the injection. Most bothersome to many patients are the loud tapping or knocking noises heard at certain phases of imaging. Ear plugs are provided to reduce the noise. Also, if you are not having you head scanned we can provide you with stereo headsets.
Q3. Who will interpret the MRI?
A subspecialty trained radiologist, who is a physician experienced in MRI and other radiologic examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician.
A preliminary interpretation may be available shortly after the exam. The completed report is sent promptly to the referring physician. Your primary physician will discuss the results of the MRI examination with you. Mink Radiology also allows for distribution of diagnostic reports and images over the Internet from our facility to your doctor.