Magnetic Resonance Imaging - Medical City Denton
Please remember that the material presented here is for informational purposes only. If you have specific questions about a medical imaging procedure, contact your physician or the radiology department of the institution where your test will be performed.
Magnetic resonance imaging (MRI) is a sophisticated diagnostic technique that uses a magnetic field, radio waves and a computer to generate detailed, cross-sectional images of human anatomy. Because it produces better soft-tissue images than x-rays can, MRI is most commonly used to image the brain, spine, thorax, vascular system and musculoskeletal system (including the knee and shoulder).
During an MRI exam, the patient is placed inside a scanner that produces a static magnetic field up to 8,000 times stronger than the earth's own magnetic field. Exposure to this force causes the hydrogen protons within the patient's body to align with the magnetic field. When a radiofrequency pulse is applied, the protons spin perpendicular to the magnetic field. As the protons relax back into alignment with the magnetic field, a signal is sent to a radiofrequency coil that acts as an antenna. This signal then is processed by a computer. Different tissues produce different signals. For example, protons in water relax more slowly than those in fat. This differentiation can be detected, measured and converted into a cross-sectional image of the patient's anatomy.
MRI is a safe procedure for most patients, although it generally is not recommended for pregnant women. If you are pregnant, let your physician know. Also, because the body is exposed to a strong magnetic field, patients who have a pacemaker, cochlear implants or aneurysm clips should check with a physician before undergoing an MRI examination. Patients who have other types of metal implants and patients who have been exposed to shrapnel or whose eyes have been exposed to metal shavings also might not be candidates for MRI; it's important to let your physician know if these conditions apply to you. For similar reasons, women undergoing an MRI exam should not wear eye shadow, because it sometimes contains metallic substances.
If you are claustrophobic or experience pain when lying on your back for more than 30 minutes, let your doctor know. He or she may be able to prescribe a relaxant or pain medication.
Before your examination, an MR technologist will explain the procedure to you and answer any questions you might have. The MR technologist will ask you several questions about your medical history. Some patients may be required to have lab work prior to procedure. It is helpful to have a list of current medications and dosages you are taking. An MR technologist, also known as a radiologic technologist, is a skilled medical professional who has received specialized education in the areas of anatomy, patient positioning, patient care, imaging techniques and MR procedures.
During the Examination
Examination time depends upon the part of the body being examined, but typically ranges from 30 minutes to an hour. You will be asked to undress, remove all jewelry and put on a hospital gown. Remember, the magnet will damage wristwatches and erase credit cards and bank cards, so don't take them into the exam room with you. You will be provided a secure place to store these items during your examination.
For most types of exams, the MR technologist will wrap a special coil around the body part that is being examined. This coil helps concentrate the radiofrequency pulses. The MR technologist then will position you on a padded, movable table that will slide into the opening of the scanner.
You may be given a contrast agent to highlight internal organs and structures. The contrast changes the relaxation rate of protons in the body, illuminating organs and tissues and making tumors, vessels and scar tissue appear brighter.
You won't feel anything during the scan, but you may hear intermittent humming, thumping, clicking and knocking sounds. These are the sounds of the magnetic gradients turning on and off. Some MR centers provide patients with headphones or earplugs to help mask the noise.
The MR technologist will not be in the room during the scan, but will be able to observe you through a window from a room next door and will be able to hear you and talk to you through a two-way microphone system. The technologist will tell you when each scan sequence is beginning and how long it will last. You will be asked to remain as still as possible throughout the sequence.
When the exam is complete, your MR scans obtained will be given to a radiologist is a physician who specializes in the diagnostic interpretation of medical images.
After your films have been reviewed by a radiologist, your personal physician will receive a report of the findings. Your physician then will advise you of the results and discuss what further procedures, if any, are needed.
Magnetic resonance imaging is a noninvasive procedure, and there are no known side effects or after effects. If a contrast agent was administered, you may experience nausea, headache or dizziness following your examination. It's important to increase your water consumption in the days following the examination. If these symptoms persist, contact your physician.
Magnetic Resonance Safety
Unlike x-ray exams, which use radiation, magnetic resonance (MR) images are created with magnetic fields and radio waves. MR scanning is a very safe and effective technique for examining the body's soft tissues, such as organs, muscles, ligaments and tendons. However, because MR scanning uses a powerful magnet, patients need to know about some special precautions and check-in procedures.
No metal is allowed in the room where MR scans are performed because metal objects are attracted to the magnet. The magnet is always on, whether or not scanning is going on. On rare occasions, patients and health care professionals have been injured when an object suddenly was drawn to the magnet. Also, metal objects can create artifacts on MR scans, making it difficult or impossible to see the patient's anatomy. For your own safety and comfort, for the safety of the staff that will care for you, and to ensure a high-quality diagnostic exam, please follow these guidelines.
You will not be allowed to wear a watch or any jewelry, including body piercing, during the exam. It may be best to leave these items at home, although some facilities provide a safe place to store your valuables during your exam. Barrettes, hairpins, eyeglasses, dentures and hearing aids also must be removed. Some types of cosmetics contain small amounts of metal, so avoid wearing any makeup the day of your exam. Also avoid clothing with metal zippers, rivets, buttons or metallic fabric. Empty your pockets of all metal items, including coins, money clips, credit cards, pens, pocket knives, keys, safety pins and paper clips.
Permanent metal dental work, such as crowns, fillings and non-removable braces, do not normally cause a problem during MR scans.
Metal wheelchairs and oxygen tanks are not permitted near the MR magnet. However, special MR-safe versions may be available at the facility where your exam will be performed. If you have questions about any medical equipment you use, ask the MR technologist who will perform your exam. He or she is a skilled professional educated in anatomy, positioning and the safe use of magnetic resonance technology.
The technologist will screen you before your exam. He or she will check you for metal objects and ask you a series of questions about metal that might be in or on your body. Think carefully about these questions, answer them truthfully and ask the technologist if there is anything you don't understand.
Be sure to tell the technologist if you have any of the following:
- A pacemaker or artificial valve in your heart.
- Metal pins, plates, rods, screws or nails anywhere in your body.
- Wire sutures or surgical staples.
- An intrauterine device (IUD) or diaphragm.
- An insulin pump.
- An aneurysm clip.
- A joint replacement.
- An ear implant.
- A stent, filter or coil in any blood vessel.
- Any type of prosthesis, including a penile implant or artificial eye.
- Permanent (tattooed) makeup, such as eyeliner or lip coloring.
It also is important to tell the technologist if you ever have suffered a gunshot wound or any type of accident that may have left metallic particles in your body. Depending on the type of metal and where it is located, you may not be able to have an MR exam. A radiologist, a physician trained in interpreting medical images, will decide if you should have the exam.
By knowing these important precautions and cooperating fully with the MR technologist, patients can help ensure that they have a safe and useful exam.