FAQS: Breast MRI

Patient Expert

Why do some women get MRIs, and others an ultrasound or nothing beyond a mammogram? Should MRI replace the mammogram as a first-line screening tool? And just how accurate are they, anyway? Everything you need to know about magnetic resonance imaging of the breast: its use as both a screening and diagnostic tool.

Q. Susan asks: My latest mammogram showed some abnormalities. I had an ultrasound, and now the doctor wants me to have an MRI. I've heard of it, but don't know what it is"

A. MRI stands for magnetic resonance imaging. Unlike CT scans or mammograms, an MRI doesn't involve X-rays. Instead, it uses a magnetic field, radio-frequency pulses, and a computer to produce a detailed image of your breast, from the inside out. Since the many images received show very thin "slices" of your breast, they can be put together and viewed from many different angles - unlike the images from an ultrasound or mammogram.

Q. It sounds like an MRI is better than either of those other two tests. Why don't doctors just start right out with an MRI?

A. Several reasons. First, an MRI is a lot more expensive, complicated, invasive, and lengthy than a mammogram or ultrasound. And it tends to deliver "false positive" results - something that looks like trouble, but isn't - up to 50% of the time.

If a mammogram and/or ultrasound alone can determine that the lump in your breast needs to be biopsied, then there's no need to complicate the situation with an MRI.

Q. So, why am I having an MRI on top of those other tests?

A. Because your doctor still isn't sure what s/he's seeing, and wants to get as much detail as possible before ordering a biopsy.

A mammogram can "see" a lump, but can't tell whether it's solid, or a fluid-filled cyst. An ultrasound can tell if a lump is solid, or a cyst. But it takes an MRI to determine if a solid mass is scar tissue, or a possible tumor, either benign, or cancerous. It can show the specific shape of a mass or lump, with some shapes more likely to be cancerous than others.

MRI can also "see" through dense breast tissue, which is problematic for both mammograms, and ultrasounds. Women with dense breasts (more glandular and connective tissue than fat) are more likely to require an MRI, for both screening and diagnostic purposes, than women whose breasts are predominantly fat tissue.

Finally, an MRI is more accurate in detecting abnormalities in women with breast implants, which can pose problems for mammograms.

If, after looking at the MRI, the doctor is still unable to determine with certainty what s/he's seeing, then a biopsy may be ordered.

One more fact, before we move on: Women at high risk for breast cancer - such as BRCA1 and BRCA2 carriers - will often have an MRI in combination with a mammogram, or will alternate the two tests on a regular basis. Since their risk is so high, it's worth the expense, and the risk of false positives, to monitor their situation closely.

Q. Do I have to prepare for an MRI?

A. Some facilities ask you to refrain from food and drink for 8 to 12 hours before the procedure; you'll receive instructions from your doctor about this.

To prevent delays or problems (and to hopefully avoid changing into a gown), it's best to wear simple, loose-fitting clothing to your MRI. You'll want to avoid all metal; that includes metal bra fasteners, zippers, snaps, or metal buttons. Earrings, bracelets, hair pins, rings, and body piercings may all need to be removed, as well.

In addition, if you use eyeglasses or hearing aides, or have removable metallic dental work, you may be asked to remove them.

Tell the radiologist about any surgical implants, medical or electronic devices, or orthopedic staples or implants you have, or any other metal that may be in your body for whatever reason. Most are fine; but some may interfere with the MRI, or could pose a risk.

Q. What's the actual procedure like?

Some breast MRIs are given with you lying on your back. But these days, many are administered as you lie facedown on a table, with your breasts fitting into cushioned openings below you.

You should try to relax and get as comfortable as possible; you'll need to remain very still during the exam, and this is much easier to do when you're relaxed. If you're at all uncomfortable, let the radiologist or person administering the exam know; s/he'll do everything possible to find you a comfortable position.

Also, although you're alone in the exam room, you'll be able to communicate with the radiologist or technologist easily via intercom.

Multiple scans, some lasting only a few seconds, some up to several minutes, will be taken. You'll hear fairly loud thumping noises when the actual scan is happening; that's when you should stay extra-still. In between, you can relax and wiggle a bit.

After a first series of scans, you'll probably be injected with a contrast material (dye), which increases the detail an MRI can pick up. In particular, the dye helps show areas where blood flow is abnormal, which can be an indication of cancer. The dye will be injected via an IV line, and more scans will be taken once it's circulated into your breast. You may feel a cold sensation when the dye is first injected; this is normal.

The dye used in MRIs, gadolinium, doesn't include iodine, unlike may other dyes; so it's safe to use if you have an iodine allergy. The radiologist will ask you about allergies ahead of time just to be safe; as well as whether you might be pregnant, and whether you have any condition (e.g., certain kidney diseases) that might preclude a dye injection.

Once all the necessary scans have been taken, you'll need to wait a bit for the images to be checked; further imaging may or may not be required. When everything's good to go, the IV will be removed, and you can get dressed and go home.

Q. How long does all of this take? Are there any side effects?

A. The whole process, start to finish, might take up to 90 minutes; or even as long as 2 hours. The actual exam lasts between 30 and 60 minutes.

Once you're done, dressed, and it's OK to leave, you're free to do anything you normally do; there's no need to take it easy after an MRI. Some women have minor side effects from the dye, including pain at the IV site (which will be a bit sore anyway). If you feel anything more than a bit of pain - for instance, if you feel itchy all over, or your skin starts to redden - contact the radiologist in charge.

Q. When will I get the results?

A. Depends on the schedules of the radiologist and your doctor. It's not immediate; like a biopsy, you usually need to wait several days.

Q. Diane asks: I've been diagnosed with breast cancer, and one of the tests I'm going to have prior to my lumpectomy is an MRI. Why do they need to do this, when they already know I have cancer, and where it is? Is it really necessary?

A. An MRI is useful in providing much more detail about your tumor: its size, shape, and specific location. An MRI can determine, for instance, if the tumor has spread into the chest wall, which will change your surgery.

If you're having a mastectomy, none of this really matters; you'll be losing your whole breast anyway. But with a lumpectomy (breast conservation surgery), where only the tumor itself and some surrounding tissue are removed, it's really helpful to be able to view the area in question in detail, from all sides.

In addition, an MRI can detect very small, very early cancers; if there are other tiny tumors in your breast, the surgeon wants to know. If there are multiple small tumors, it might make mastectomy a better option than lumpectomy.

Finally, women who are having chemotherapy to shrink their tumor prior to surgery will often be monitored via MRI, to see how the treatment's working.

One final note: Although most insurance plans cover the cost of a breast MRI, some don't. The procedure will cost upwards of $2,000, perhaps more, so it's a good idea to clear it through your insurance company beforehand.