Mammogram vs. Breast MRI

Advantages, Limitations, Cost, and Accuracy

In This Article

Although a mammogram is considered the standard test for breast cancer screening, another technology known as breast magnetic resonance imaging (MRI) is increasingly being used in women who are at increased risk. Although MRIs are capable of detecting tumors that mammograms sometimes miss, they are undermined by their high cost and an increased potential for false-positive results (those that report cancer even when cancer is not present).

While both can be used to detect breast cancer, mammograms and MRIs have their own distinct purposes, indications, advantages, and limitations. Neither is inherently "better" than the other. The question is more about when a test is appropriate and whether it can deliver a high degree of reliability without exposing a woman to undue procedures or costs. A relatively new procedure referred to as fast MRI or abbreviated MRI may help bridge some of these differences in the future.

Here are some of the key differences you should know about.

Procedures

During a mammogram, X-ray radiation is used to penetrate breast tissue and record differences in tissue density. Solid tumors will typically have a higher density than normal tissue and show up on an X-ray as a lighter, solidified mass.

Different views of your breast are taken to ensure all aspects have been covered. To obtain the best image, the breast is compressed to allow radiation to penetrate a thinner layers of tissue.

With an MRI, compression is not needed. Rather, you are placed in a tube-like machine that emits powerful magnetic and radiation waves to generate highly detailed cross-sectional images of the breast.

To differentiate tissue density, you are given an injectable contrast dye, usually gadolinium, that can enhance the image resolution by 10- to 100-fold compared to a mammogram. Once the test is complete, the gadolinium is cleared from your system in urine.

In terms of timing, mammograms take between 30 to 60 minutes to complete, whereas a breast MRI may take 45 to 90 minutes. While mammograms may cause discomfort, an MRI can make some people claustrophobic.

Test Sensitivity

Generally speaking, a mammogram has a sensitivity of around 87 percent in the average woman. Sensitivity is the term used to describe the percentage of time a test makes a correct positive diagnosis.

In women with dense breasts (seen on a mammogram as areas of opacity and striation), the specificity can drop to anywhere from 48 percent to 64 percent, according to a 2015 review of studies in the American Journal of Roentgenology.

Because MRI offers a higher resolution, it is better able to visualize masses in dense tissue. When compared to a mammogram, a breast MRI has a specificity closer to 93 percent, says a 2013 study in the Journal of Thoracic Surgery.

False Positives

Despite its imaging capabilities, breast MRIs are notoriously variable when it comes to specificity—that is, the percentage of times a test correctly yields a negative result.

What this means is that an MRI is prone to false-positive results. According to the current body of evidence, the specificity can range anywhere from as high as 97 percent to as low 37 percent. The main reason for this is that an MRI will enhance both benign and cancerous lesions, often with little differentiation in their characteristics.

A mammogram has slightly better specificity than an MRI (75 percent), mainly because it can detect calcification (the characteristic deposit of calcium around a malignancy) that can help differentiate benign and cancerous tumors.

In the end, mammograms have their fair share of false positives, but they have a far less variability compared to a breast MRI.

Possible Risks

Women often worry that exposure to radiation during a mammogram can place them at risk of developing cancer. Most of the current evidence suggests that the risk of this is low, even with annual mammogram screening.

According to a 2016 study in the Annals of Internal Medicine, around 125 of every 100,000 women who undergo an annual mammogram will develop radiation-induced breast cancer (0.00125 percent). Of those, 16 (0.00016 percent) will die.

There has also been an ongoing debate as to whether gadolinium used in MRI poses a health risk. The concerns first arose in 2014 when a study reported that the contrast dye could be retained and deposited in the brain. While there has yet to be any evidence of this being harmful, most current research suggests that it is not.

Despite this, the U.S. Food and Drug Administration issued a safety announcement in 2017, recommending that patients be advised about gadolinium retention prior to undergoing an MRI.

Costs

Any health screening tool must fulfill three criteria to be effective in a public health setting: reliability, availability, and affordability. By and large, a mammogram fulfills these aims.

From a cost perspective, a mammogram is relatively affordable, ranging from $75 to $250, depending on the facility and where you live. By contrast, a breast MRI with contrast dye may cost you anywhere from $750 to $2,500 or more.

While newer rapid breast MRI tests are becoming more affordable, many insurance companies will not cover a breast MRI of any sort unless an abnormality is found. This is one of the reasons why a mammogram remains as important as it does, despite its technical limitations.

According to a 2019 study in Cancer, routine mammogram screenings reduce the risk of breast cancer by no less than 60 percent over 10 years.

When to Have a Breast MRI

Women who are at high risk for developing breast cancer should consult their doctors about having a breast MRI in addition to a standard mammogram. High-risk individual includes those who:

  • Have the genetic mutations BRCA1 and BRCA2
  • Have one of the other genetic mutations associated with breast cancer, such as CHEK2, PALB2, ATM, and others
  • Have a first-degree relative with a familial breast cancer mutation
  • Had radiation therapy to the breast between the ages of 10 and 30, such as to treat Hodgkin lymphoma
  • Have a lifetime breast cancer risk of 20 percent to 25 percent based on assessment tools issued by the National Cancer Institute

Women who have had breast cancer or conditions that predispose them to the disease (such as atypical ductal hyperplasia) may also need an MRI. Women who have had a mastectomy on one side are often offered regular MRIs on the contralateral (non-involved) breast. Those with dense breasts on a mammogram may also need a breast MRI.

Breast MRI is commonly performed if a mammogram and a subsequent breast ultrasound reveal a breast abnormality.

Conventional vs. Fast Breast MRI

Women who have dense breasts have both an elevated risk of developing breast cancer, but mammograms are less sensitive. In some states, women who are found to have dense breasts on mammography are now required to be informed of the diagnosis and may wish to undergo additional testing. In the past, combining mammography and breast ultrasound was found to improve detection to some degree, but with an increased risk of false positives.

A newer MRI technique referred to as fast breast MRI or abbreviated MRI may be combined with mammography in this situation. Unlike conventional MRI, a fast MRI takes only around 10 minutes to perform, and unlike the high cost of conventional MRI, fast MRI costs roughly the same as a mammogram. In studies thus far, the combination of mammography with fast MRI detected significantly more breast cancers than mammography alone (or combined with ultrasound), especially aggressive breast cancers. Since the technique is relatively new, however, it is not yet available at all breast cancer screening institutions.

A Word From Verywell

Since recommendations on when to do an MRI for breast cancer screening are relatively new, it's important to be your own advocate if you feel that you need one.

The same applies to identifying the genetic mutations that can place you at risk. There are a number of genetic tests today that can detect 20 to 40 key mutations associated with breast cancer. By working with your doctor and a genetic counselor, you can have a clearer picture of your screening needs. It's important to note that at-home-screening tests such as 23andme are not adequate to screen for a genetic predisposition to breast cancer. In fact, it's thought that these tests likely miss around 90 percent of BRCA mutations as well as other non-BRCA mutations that raise breast cancer risk.

For women at risk of breast cancer, groups such as FORCE (Facing Our Risk of Cancer Empowered) can provide both information and the means to connect with others facing similar questions and concerns.

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Article Sources

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