 Magnetic Resonance (MR) Imaging
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MR, or magnetic resonance imaging, is a routine diagnostic procedure. Images of the internal tissues of the human body are produced by using the tiny magnets of hydrogen nuclei which are abundant in all of us as parts of water, fat, protein, and other molecules. The large magnetic field of the MR machine causes the hydrogen magnets to align, while applied radiowaves excite them to transmit signals similar to the radiowaves generated at FM radio stations. The locations of the signals within the body are identified using magnetic field gradient pulses which are the source of the loud knocking noises heard during the examination. Once enough signals have been collected, they are processed by powerful computers to generate pictures of the human anatomy in vivid detail for the radiologist to analyze and diagnose abnormalities.
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Your physician may request an MR study for a number of reasons. MR is often used to obtain specific diagnostic information not already provided by other imaging technologies such as ultrasound, computed tomography, and nuclear medicine. MR may be needed to rule out disease and to facilitate medical, surgical, and other treatments for conditions of the brain, spinal column and spinal cord; eye, ear, nose and throat; bones, joints, and muscles; heart and blood vessels; chest and lungs; abdominal organs and digestive tract; and, kidneys , urinary tract, and pelvic organs. Such conditions may include congenital and developmental disorders, genetic and metabolic diseases, infections and inflammatory conditions, traumatic and other types of injury, vascular and blood diseases, and cancer conditions of childhood.
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You or your child may eat or drink as usual unless the MR examination requires the injection or ingestion of a contrast agent for image enhancement, if sedation or anesthesia is necessary, or if there are other special care considerations. In these situations, specific dietary restrictions and other instructions are provided by your physician in advance of the appointment. It is very important to adhere to these instructions to insure your or your child's saftey while undergoing the MR examination. Otherwise, the procedure will be rescheduled to a time and date that allows for the appropriate preparation. It is also important to notify the MR staff of any active illness, allergy, or previous drug reaction that may prevent the child from undergoing the examination safely.
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Upon arriving at the MR suite, your appointment and registration are confirmed by the MR scheduling coordinator. You will be asked to fill out the MR screening questionnaire. All individuals who will be entering the MR room (i.e. the patient and their attendant/s) must fill out this form. This form is meant to screen individuals for items on or within the body such as cardiac pacemakers, metal implants and ferromagnetic objects. Some of these items may malfunction or move within the magnetic field and are considered a strong relative contraindication to having an MR exam.
After the questionnaire is completed, the MR nurse will ask a few questions and will perform a clinical screening examination.
You or your child and all individuals entering the MR room must remove all metal objects (e.g. jewelry) and electronic devices (e.g. watch) and change into hospital attire or wear clothing from home that is comfortable and free of metal (zippers, buttons, etc.). The nurse then prepares you or your child for the MR procedure, which may include oral or intravenous sedation. Sedation is supervised by an anesthesiologist and administered by a registered nurse or nurse practitioner. Anesthesia, which is sometimes required, is administered by an anesthesiologist.
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The MR technologist positions and secures you or your child comfortably on a narrow bed within the large, doughnut-shaped magnet and adjusts the radiofrequency coil, which will be placed over, under or around the body part to be examined. The technologist then performs the MR examination with the radiologist and is in contact with the patient at all times. During the MR procedure, the patient will hear several series of repetitive knocking noises. It is particularly important for the patient to remain still during these noises since the MR machine is obtaining images at those times. If the pictures are motion-free, this will help shorten the total exam time and prevent delays.
An entire MR examination may take from twenty minutes to one and a half hours depending on the type of information required by the radiologist and your physician. All patients undergoing sedation or anesthesia receive continuous vital monitoring and support.
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If an injection is required, you or your child may feel minor discomfort from the needle. MR itself is a painless procedure, in that the patient is not touched. Rather loud pulsations are routinely heard but can be reduced with ear plugs or ear phones provided by the MR staff. Occasionally, claustrophobia is a problem. If there is concern about this possibility, the MR staff should be contacted in advance of the appointment for information and assistance.
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MR, like other imaging technologies in radiology, is FDA approved for its safety and effectiveness. It has been used to image patients since 1981 and no adverse biological effects have been reported from exposure to the magnetic fields or radiowaves.
It is considered safe, provided all safety protocols are adhered to. That is why the screening form mentioned above, meant to screen individuals for items on or within the body such as cardiac pacemakers, metal implants and ferromagnetic objects, is so important. These objects may move during the procedure unless firmly anchored in the tissues. The magnetic fields tend to cause malfunction of programmable devices. Some devices (e.g. Baclofen pumps, Medos valves) can be safely imaged but may need to be switched off during the procedure or reprogrammed after the procedure. Cardiac pacemakers are a strong relative contraindication to having an MR.
Some metallic devices are safely imaged but produce artifact that may obscure the region of interest (e.g. dental braces in patients for pituitary imaging).
Finally, surface or implanted objects with coiled wires can result in electrical burns due to heating and/or induction of currents as a result of radiofrequency effects.
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After the images are obtained, you are free to go and resume your normal activity.
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The interpretation of an MR examination involves the review of multiple images and often requires additional computer processing. After a careful analysis of your MR images, the radiologist will review the findings with the physician who requested the study and provide a report. You or your child's physician will then discuss the results with you.
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