Magnetic resonance imaging (MRI) of the breast is a test that detects breast cancer and other abnormalities in the breast. A breast MRI captures multiple images of your breast that a computer combines to generate detailed pictures.
A breast MRI usually is performed after you have a biopsy that’s positive for cancer, and your doctor needs more information about the extent of the disease. In certain situations, such as for women with high risk of breast cancer, a breast MRI may be used with mammograms as a screening tool for detecting breast cancer.
What Is a Breast MRI?
An MRI is a noninvasive medical test that helps physicians diagnose and treat medical conditions. MRI uses a powerful magnetic field, radio frequency pulses, and a computer to produce detailed pictures of organs, soft tissues, bone, and virtually all other internal body structures. MRI does not use ionizing radiation (x-rays).
Detailed MRI images allow physicians to evaluate various parts of the body, and determine the presence of certain diseases. The images are examined on a computer monitor, transmitted electronically, and printed or copied to a CD.
MRI of the breast offers valuable information about many breast conditions that cannot be obtained by other imaging modalities, such as mammography or ultrasound.
Why Would my Doctor Order an MRI?
MRI of the breast is not a replacement for mammography or ultrasound imaging, but a supplemental tool that has many important uses, such as:
- Screening in women at high risk for breast cancer. For women at high risk for breast cancer because of a strong family history, MRI may be an appropriate tool to screen for breast cancer. Your radiologist or primary care doctor can look at your family history and determine if screening MRI may be appropriate for you.
- Determining the extent of cancer after a new diagnosis of breast cancer. A breast MRI may be performed to determine how large the cancer is; whether it involves the underlying muscle; if there are other cancers in the breast, and whether there is a cancer in the opposite breast; and if there are abnormally large lymph nodes in the armpit, which can be a sign cancer has spread to that site.
- Evaluating hard-to-assess abnormalities seen on mammography. Sometimes an abnormality seen on a mammogram cannot be adequately evaluated by additional mammography and ultrasound alone. In these rare cases, MRI can be used to definitively determine if the abnormality needs biopsy or can safely be left alone.
- Evaluating lumpectomy sites in the years following breast cancer treatment. Scarring and recurrent cancer can look identical on mammography and ultrasound. If there is a change in a lumpectomy scar found by mammography or on a physical exam, MRI can determine whether the change is normal maturation of the scar, or a recurrence of the cancer.
- Following chemotherapy treatment in patients getting neoadjuvant chemotherapy. In some cases, breast cancer will be treated with chemotherapy before it has been removed by surgery. This is called neoadjuvant chemotherapy. In these cases, MRI is often used to monitor how well the chemotherapy is working, and to re-evaluate the amount of tumor still present before the surgery is performed.
- Evaluating breast implants. MRI is the best test for determining whether silicone implants have ruptured.
What Should I Expect During my Breast MRI?
Breast MRI examinations require the patient to receive an injection of contrast material into the bloodstream. The traditional MRI unit is a large cylinder-shaped tube surrounded by a circular magnet. You will lie on a moveable examination table that slides into the center of the magnet. The computer workstation that processes the imaging information is located in a separate room from the scanner.
Most MRI exams are painless. However, some patients find it uncomfortable to remain still during MRI imaging. Others experience a sense of claustrophobia. Patients who anticipate anxiety can be sedated, but fewer than one in 20 require medication. You will be offered earplugs to reduce the noise of the MRI scanner, which produces loud thumping and humming noises during imaging.
You will be positioned on the moveable examination table. Bolsters may be used to help you stay still and maintain the correct position during imaging.
For an MRI of the breast, you will lie face down on a platform specially designed for the procedure. The platform has openings to accommodate your breasts and allow them to be imaged without compression. The electronics needed to capture the MRI image are actually built into the platform. It is important to remain still throughout the exam, so make sure you are comfortable and can relax. Be sure to let the technologist know if something is uncomfortable, since discomfort increases the chance that you will move during the exam.
A nurse or technologist will insert an intravenous catheter, also known as an IV line, into a vein in your hand or arm. You will be moved into the magnet of the MRI unit, and the technologist will perform the examination while working at a computer outside of the room. Contrast material will be injected into the IV after an initial series of scans. Additional series of images will be taken during or following the injection. When the examination is complete, you may be asked to wait until the technologist or radiologist checks the images, in case additional images are needed. Your IV will be removed.
MRI exams generally include multiple runs, some of which may last several minutes. The imaging session lasts 30 minutes to an hour.
Who Interprets the Results and How Do I Get Them?
A breast radiologist, a physician specifically trained to supervise and interpret your examination, will analyze the images and send a report to your primary care or referring physician, who will share the results with you.
Follow-up examinations may be necessary, and University Breast Care will contact you and explain why another exam is requested. Sometimes a follow-up exam is done, because a suspicious or questionable finding needs clarification with additional views or a special imaging technique.
What Are the Benefits Versus Risks?
- MRI is a noninvasive imaging technique that does not involve exposure to ionizing radiation.
- MRI has proven valuable in detecting and staging breast cancer, particularly when other imaging studies, like mammography or ultrasound, fail to provide adequate information.
- MRI as an addition to mammography has been shown to be useful in evaluating women at high risk for breast cancer.
- MRI can successfully image the dense breast tissue common in younger women, and it can successfully image breast implants. Both of these are difficult to image using traditional mammography.
- If a suspicious lesion is seen, MRI can provide guidance for biopsy.
- The contrast material used in MRI exams is less likely to produce an allergic reaction than the iodine-based contrast materials used for conventional x-rays and CT scanning.
- The MRI examination poses almost no risk to the average patient when safety guidelines are followed.
- Although the strong magnetic field is not harmful, implanted medical devices that contain metal may malfunction or cause problems during an MRI exam.
- There is a slight risk of an allergic reaction to contrast material. Such reactions usually are mild and easily controlled by medication. If you experience allergic symptoms, a radiologist or other physician will be available for immediate assistance.
- Nephrogenic systemic fibrosis is a recognized, but rare, complication of MRI believed to be caused by the injection of high doses of gadolinium-based contrast material in patients with poor kidney function. Careful assessment of kidney function before considering a contrast injection minimizes the risk of this rare complication.
- Manufacturers of intravenous contrast say mothers should not breastfeed their babies for 24-48 hours after contrast medium is given. However, both the American College of Radiology and the European Society of Urogenital Radiology note that available data suggests it is safe to continue breastfeeding after receiving intravenous contrast.
What Are the Limitations of MRI of the Breast?
- High-quality images are assured only if you remain perfectly still and follow breath-holding instructions while the images are being recorded. If you are anxious, confused or in severe pain, you may find it difficult to lie still during imaging.
- A person who is very large may not fit into the opening of certain types of MRI machines.
- The presence of an implant or other metallic object sometimes makes it difficult to obtain clear images. Patient movement can have the same effect.
- Although there is no reason to believe that magnetic resonance imaging harms the fetus, pregnant women usually are advised not to have an MRI exam during the first trimester unless medically necessary.
- MRI may not always distinguish between cancer tissue and fluid, known as edema.
- MRI typically costs more and may take more time to perform than other imaging modalities.
- Sometimes a benign piece of tissue in the breast can take up the contrast material and show up as a bright spot on the image. Often, the radiologist can tell by the appearance of the tissue whether it is cancer or not. When it is not possible, other testing such as ultrasound of that specific spot or a biopsy may be needed. If additional testing or biopsy shows no cancer, it is called a false-positive test result.