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Magnetic Resonance Imaging (MRI) is an advanced diagnostic imaging technique that uses magnetic fields and radiofrequency energy to create detailed images of the body. A patient is positioned within a magnetic field. Radiofrequency pulses are used to temporarily alter the magnetic field, generating signal, which allows images to be created. MRI is most commonly used to image the brain, spine and joints. However, MRI is also very useful to generate images of the heart, blood vessels, abdomen, pelvis, and of the breasts. MRI does not use ionizing radiation and the magnetic fields are not known to be harmful.
MRI is performed at most sites served by Clinical Radiologists. The larger hospitals and clinics have fixed magnets that operate daily. Some smaller sites use mobile magnets on trucks that may be available one or a few days per week. The MRI department at Memorial Medical Center is accredited by the American College of Radiology.
There are two general types of MRI machines (referred to by radiologists as “magnets”) high field strength and low field strength or “open” magnets. The best images are generally obtained from high field strength magnets since these magnets provide the greatest amount of signal for image creation. The high field strength magnets are relatively enclosed; some larger patients may not fit into these magnets and some patients with severe claustrophobia may be uncomfortable in them. The open, or low field strength magnets will accommodate larger patients and may be easier for some claustrophobic patients. Certain types of exams can be performed only on high field strength magnets. Most of our sites use high field strength magnets, although open magnets are available in Springfield, Quincy and Jacksonville.
All radiologists receive training in MRI during their residencies. Several members of Clinical Radiologists have additional fellowship training for special expertise in different areas of MRI. We have radiologists who are experts in MRI of the central nervous system (brain and spine), MRI of the musculoskeletal system, MRI of the abdomen and pelvis, MRI of the heart and blood vessels and MRI of the breast.
What preparation is needed for the examination?
For most MRI examinations no special preparation is required. For MRI examinations of the abdomen and pelvis you may be asked to be fasting for several hours prior to the examination. Fasting can decrease the amount of artifact, or image noise, from bowel.
If you are a welder or metalworker, or if you have ever had a metal foreign body in your eyes, you may need to have an x-ray of your eyes prior to having an MRI. If there is a metallic object in the eyeball, you may not be able to have an MRI.
Certain other patients cannot undergo MRI examinations. If you have a cardiac pacemaker, an aneurysm clip in the brain, cochlear implants, a TENS unit and certain other types of implants, stimulators or pacemakers you may not be able to have an MRI.
Metal objects and magnetic objects cannot be taken into the room with the magnet and could interfere with your examination. Therefore you will be asked to remove metal objects such as jewelry, watches, keys and credit cards. For some exams, certain types of eye makeup may have to be removed. If there is any metal in your clothing, you may need to change into a gown for the examination.
What if I am pregnant?
MRI appears to be safe during pregnancy and in fact is sometimes used to generate images of fetuses. However, it seems prudent to avoid exposing fetuses to strong magnetic fields as much as possible. We generally do not perform MRI on pregnant women in the first trimester except in urgent situations. We do more commonly perform MRI on pregnant women in their second and third trimesters, although in some cases the examination may be postponed until after delivery.
What happens during the MRI examination?
The MRI scanner looks like a short tunnel which is open on both ends and has lights and circulating air inside. You will be placed on the scanner table and a radiofrequency coil will generally be put around the area to be imaged. The table then slides into the scanner and the imaging begins. You will generally need to be as still as possible, since movement can result in poor quality images. For some exams you will hold your breath at times and for other exams you will just lie still and breathe normally. Some examinations will require an injection of intravenous contrast or dye. The contrast agent used for MRI is very safe.
The MRI will make a series of loud banging or pounding sounds during the examination. You will be given earplugs to wear and will be allowed to listen to music during the examination. At some sites you may be able to bring a favorite compact disc or cassette tape to listen to during the examination. You will be able to communicate with the technologist at all times during the exam.
What if I am claustrophobic?
Almost all patients can tolerate the MRI examination by listening to music and perhaps covering their eyes with a cloth. Some patients are too anxious in enclosed spaces and require a sedative. If you are very anxious in enclosed spaces, let your doctor know. Your doctor may be able to prescribe a sedative to be taken by mouth prior to the MRI.
We can also provide oral sedatives to patients at several of our facilities. Occasionally a patient needs stronger sedatives and/or pain medicines administered intravenously. We have the facilities to use intravenous sedation and to monitor patients during and after such an exam at Blessing Hospital and Memorial Medical Center.
MR angiography (MRA) refers to the use of MRI to study arteries throughout the body. Clinical Radiologists has been performing MRA for years and has performed thousands of MRA exams. We use MRA to investigate arteries in the head, neck, chest, abdomen, pelvis and extremities. MRA can be used to investigate all types of arterial disease, including blockages, aneurysms, dissections, emboli (clots) and injuries from trauma.
MRA examinations of the head and neck may not involve the use of a contrast agent, relying instead on the magnetic properties of flowing blood to demonstrate the arteries. MRA examinations of other parts of the body involve performing MRI examination sequences before and after injection of a contrast agent (gadolinium) through an IV. We then perform rapid MR imaging while the contrast agent is within the arteries to be studied. To a patient, an MRA exam will feel like any routine MRI. After the exam, we will use powerful computers to look at the image data and to reformat the image data into two dimensional or three dimensional pictures of the blood vessels.
MRA allows us to get information about arteries that was once available only by placing a catheter directly into the artery and injecting the dye into the artery. MRA can often give the same information with less cost, fewer risks/complications and less time in the radiology department and hospital. Of course, Clinical Radiologists has several radiologists with advanced fellowship for interpretation of MRA of the central nervous system and of the body and extremities.
Cardiac MRI refers to use of MRI to evaluate the heart and some of its surrounding structures. Cardiac MRI can be used to evaluate heart muscle, heart valves, heart tumors, heart function and abnormalities of the sac surrounding the heart.
Cardiac MRI is difficult to do and requires state-of-the-art equipment, well trained technologists and skilled radiologists with appropriate advanced training. Clinical Radiologists has been performing cardiac MRI for several years and does have radiologists with advanced training in MRI and cardiac imaging.
Please see the section on Magnetic Resonance Imaging for general information about MRI. MRI can be used to image the breasts for tumors and to look at breast implants. Although MRI of the breasts has been extensively studied, and is becoming more commonly performed, it remains a very advanced and specialized imaging technique, available only at certain specialized facilities. Clinical Radiologists does have breast imaging specialists who have expertise in MRI of the breast, and we have performed breast MRI for several years. In fact Clinical Radiologists has been participating in a nation-wide study by the American College of Radiology Imaging Network (ACRIN) to evaluate MRI of the breast in some women with breast cancer. We are one of only 25 sites with the equipment, technical expertise and clinical expertise to be asked to participate in that trial.
MRI of the breasts is performed because it will sometimes show things that mammograms and breast ultrasound do not. When an area of concern is seen, it may require biopsy or localization for surgical removal. Many sites that perform MRI of the breast are unable to use MRI to guide biopsy or localization of lesions that are seen only with MRI. We do have the necessary equipment and expertise to perform MRI-guided breast biopsy and localization at Memorial Medical Center in Springfield.
When should MRI of the breast be performed?
Mammography is the only imaging study that is currently appropriate for screening of women at large for breast cancer. However, there are several indications for breast MRI. Those indications are as follows:
- Evaluation of breast implants.
- Pre-operative evaluation for possible multifocal/multicentric disease. Differentiation between scar tissue and recurrent cancer after lumpectomy.
- Evaluation of some breast cancers in patients with dense breast tissue on mammograms.
- Following tumor response to chemotherapy given prior to surgery for breast cancer (when tumor size cannot be measured with physical exam, ultrasound or mammograms.)
- Looking for recurrent cancer in the chest wall after mastectomy.
- Some patients with infiltrating lobular cancer.
- Patients who are BRAC I or II positive.
- Some patients who have a very strong family history of breast cancer and who have dense breast tissue that is difficult to evaluate with mammography.
- Patients with tumor cells in lymph nodes in the axilla (armpit) but no breast cancer seen with mammography.
What happens during the examination?
The examination will take up to an hour. You will lie on your stomach with your breasts in a specially designed “holder” called a breast coil. The coil works with the magnetic field created by the MRI magnet to generate high quality images of the breast. If the test is being performed because of a concern about breast cancer, you will receive an injection of MRI contrast material through an IV. The injection is safe and painless. If the test is being performed to evaluate a breast implant, the contrast injection is generally not necessary.
What preparation is needed for the examination?
No special preparation is required. If the test is being performed because of a concern about breast cancer, an intravenous line will be started prior to the exam. Women should generally undergo MRI of the breasts during days 7-14 of the menstrual cycle.