What is an MRI?
Magnetic resonance imaging (MRI) is a non invasive, usually painless medical test that helps physicians diagnose and treat medical conditions. MRI uses a powerful magnetic field, radio waves and computer to produce detailed images of organs, soft tissues, bone and much more. The images can then be examined on a computer monitor. MRI does not use ionizing radiation (x-rays). MRI allows physicians to better evaluate parts of the body and certain disease that may not be assessed adequately with other imaging methods such as x-ray, ultrasound, or computed tomography (CT)
Common uses of the procedure:
MRI is most frequently used to image the spine and spinal cord, brain, joints, and soft tissue of extremities. However, MRI can be utilized in most any body part.
What does the equipment look like?
Southwest Medical Center currently has a SHORT bore MRI, installed in August of 2011. You will be placed on the table and the body part of interest will be in the middle of the machine. The machine looks like a doughnut, open on both sides. The body part that is being imaged must be placed in a coil to increase the magnetic field. The head coil will probably remind you of wearing a football helmet.
What will I experience during the exam?
Most MRI exams are painless. Some patients, however, find it uncomfortable to remain still during MR imaging. Others experience a sense of being closed-in (claustrophobia). Therefore, sedation can be arranged for those patients who anticipate anxiety, but fewer than one in 20 require it. It is normal for the area of your body being imaged to feel slightly warm, but if it bothers you, notify the technologist. It is important that you remain perfectly still while the images are being recorded, which is typically only a few minutes at a time. You will know when images are being recorded because you will hear tapping or thumping sounds when the coils that create the magnetic field are turned on. You will be asked to wear hearing protection during the exam. Headphones with music or earplugs will be provided. If you would like to listen to your own music, you may bring in your personal iPod to connect to the system.
You will be able to relax between imaging sequences. You will be alone in the exam room during the MR imaging, however the technologist will be able to see, hear and speak with you at all times using a two-way intercom. When the contrast material is injected, it is normal to feel coolness and a flushing for a minute or two. The intravenous needle may cause you some discomfort when it is inserted and once it is removed, you may experience some bruising. There is also a very small chance of irritation or infection of your skin at the site of the IV tube insertion.
If you have not been sedated, no recovery period is necessary. You may resume your usual activities and normal diet immediately after the exam. A few patients experience side effects from the contrast material, including nausea and local pain. Very rarely, patients are allergic to the contrast material and experience hives and itchy eyes. It is recommended that nursing mothers not breastfeed for 36 to 48 hours after an MRI with a contrast material.
Women should always inform their physician and technologist if there is any possibility of pregnancy. The risk of an MRI exam to the baby is unknown, pregnant women should not have this exam unless the potential benefit from the MRI is assumed to outweigh the risks.
Southwest Medical Center has a new SHORT bore MRI, creating more space around the patient to decrease anxiety. However, if you have claustrophobia (fear of enclosed spaces) or anxiety, you may want to ask your physician for a prescription for a mild sedative. A large window is also in the exam room to create a more open feeling and decrease anxiety.
How is the procedure performed?
MRI examinations are usually done on an outpatient basis. You will be positioned on the moveable examination table. Straps and bolsters may be used to help you stay still and maintain the correct position during imaging. Small devices that contain coils capable of sending and receiving radio waves may be placed around or adjacent to the area of the body being studied. If a contrast material will be used in the MRI exam, a nurse or technologist will insert an intravenous line into a vein in your hand or arm. You will be moved into the magnet of the MRI unit and the technologist will leave the room while the MRI examination is performed. If a contrast material is used during the examination, it will be injected into the intravenous line (IV) after an initial series of scans. Additional series of images will be taken following the injection. When the examination is completed, you may be asked to wait until the technologist checks the images in case additional images are needed. MRI exams generally include multiple runs (sequences), each will last a few minutes. The entire examination usually lasts between 20 – 45 minutes. Some studies do last longer.
How should I prepare for the Procedure?
You may be asked to change into a gown or you may be able to stay in your clothing, if it is loose fitting and has no metal fasteners or zippers. Generally you may follow your regular diet prior to the MRI. There are a few special instances where you may have to stop eating and drinking for 6-8 hours, you will be instructed as such when you schedule your appointment if this is needed. Some MRI examinations may require the patient to have an injection of contrast into the bloodstream. The contrast is called gadolinium, and does not contain iodine and is less likely to cause an allergic reaction. Please notify the technologist of any serious health problems such as kidney disease, diabetes, and sickle cell anemia, as this may prevent you from having an MRI with contrast material. The entire examination usually lasts between 20 – 45 minutes, depending on the body part being imaged. Some studies do last longer.
For some patients a lab test to evaluate your renal (kidney) function may be required prior to the injection of the radiology contrast material.
Patients with a history of any of the following will require a lab test within 30 days prior to the exam.
1. Age 70 or older
2. History of kidney/renal disease, single kidney, kidney/renal surgery (kidney removed, tumor or transplant)
3. History of or taking medication for hypertension (high blood pressure)
4. History of or taking medication for hyperureicemia (gout, or high levels of uric acid in blood stream)
5. Taking medication containing Metformin (for diabetes)
6. History of liver disease, liver transplant, or impending liver transplant.
Who interprets the MRI?
A radiologist, who is a physician experienced in MRI and other imaging examinations, will analyze the images and send a signed report with his/her interpretation to your primary care physician. Your physician’s office will inform you how to obtain the results.
Metal and electronic items are not allowed in the MRI exam room as they may interfere with the magnetic field of the MRI and cause a safety risk to the patient and staff. Jewelry and other accessories should be left at home if possible.
**Other items that are not allowed in the MRI exam room are:
Watches, credit cards, hearing aids, pins, hairpins, metal zippers and similar metallic objects, removable dental work, pens, pocketknives, and eye glasses.
In most cases, an MRI is safe for patients with metal implants (depending on age of implant), except a few types: People with the following CANNOT be scanned and should not enter the MRI exam room: pacemaker, internal defibrillator, cochlear (ear) implant, clips used on brain aneurysms.
You should tell the technologist if you have any medical electronic devises in your body, because they may interfere with the exam or potentially pose a safety risk. Examples include: artificial heart valves, implanted drug infusion ports, infusion catheter, intrauterine device (IUD), implanted electronic device, including a cardiac pacemaker, artificial limbs or metallic joint prostheses, implanted nerve stimulators, metal pins, screws, plates or surgical staples.
In general, metal objects used in orthopedic surgery pose no risk during an MRI. However a recently placed artificial joint may require the use of another imaging procedure. If there is any question of their presence, an x-ray will be taken to detect the presence of metal objects.
Sheet metal workers and others who might have metal objects such as shrapnel in their bodies may also require an x-ray prior to an MRI. Dies used in tattoos may contain iron and could heat up during an MRI, but this is rarely a problem. Tooth fillings and braces usually are not affected by the magnetic field, but they may distort images of the facial area or brain, so the radiologist should be aware of them.
Medical patches (pain medication, nicotine) should be removed prior to entering the MRI exam room as they may heat up during the exam causing a burn to the skin.
How does the MRI work?
Unlike conventional x-ray examinations and computed tomography (CT) scans, MRI does not depend on radiation. Instead, radio waves are directed at protons, the nuclei of hydrogen atoms, in a strong magnetic field. The magnetic field is produced by passing an electric current through wire coils in most MRI units. Other coils, located in the machine and in some cases, placed around the part of the body being imaged, send and receive radio waves. As you lie inside the MRI unit, radio waves are directed at the protons in the area of your body being studied. In the magnetic field, these protons change their position, producing signals that are detected by the coils.
A computer then processes the signals and generates a series of images each of which shows a thin slice of the body. Because protons are most abundant in water molecules, MR images show differences in water content between various body tissues. As a result, MRI is especially suited to detecting disorders that increase fluid in diseased areas of the body, for example, areas affected by tumors, infection and inflammation. Overall, the differentiation of abnormal (diseased) tissue from normal tissues is significantly easier with MRI than with other imaging modalities such as x-ray, CT and ultrasound.