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The Many Shades of Breast Imaging Studies:

A Comparison of Mammogram vs. Ultrasound vs. Breast MRI

Article by: Laura Thomas, MD

Breast radiologists - the physicians who specialize in screening and diagnosing women with breast cancer - are used to seeing shades of black, white, and grey all day long. But what does that mean when it comes to breast imaging?

Color, or the absence of color, means everything in imaging studies. Breast abnormalities such as calcifications, lesions, or masses may show up differently – or not at all— depending on the imaging modality being used.

While most patients are familiar with mammography, radiologists also use ultrasound and magnetic resonance imaging (MRI) to evaluate breast tissue in an effort to detect breast cancer as early as possible. With that said, patients may wonder what the differences are between these techniques and how to know which study might be best for them.

In most cases, the answer to which study is best isn’t a simple or straightforward decision. Due to the complexities around breast imaging, your OB/GYN or primary care doctor will work with your radiologist to determine which imaging tool is best for you based on your overall risk of breast cancer and/or your current breast complaint.

Among the three modalities: mammography, ultrasound, and MRI, none are necessarily “better” than the other, but instead, they work together as needed to give the radiologist a full picture of your breast tissue. Each tool uses a different technology to look at the breast and they are complementary. As indicated, each study tells us something different as we piece together information to help patients get the diagnoses they need.

Mammogram – What is it and Who Needs One?

Mammogram is the best method for overall breast cancer screening. While some women with dense breast tissue or a family history of breast cancer may think they need an ultrasound or a breast MRI in lieu of a mammogram, the mammogram is typically the best place to start for most women. Following the mammogram screening, other imaging studies can be added as needed for certain patients.

Mammography is the imaging tool that’s been most widely studied and is the only modality proven effective for decreasing breast cancer mortality rates. 3D mammography is proving to be an even more effective method of screening with an enhanced ability to detect cancers.

The American College of Radiology recommends all women age 40 and above (of average risk) should get a mammogram each year to screen for breast cancer. Certain high-risk patients may need to start even earlier (your primary care physician or OBGYN can advise you on when to start).

How does it work? The mammogram uses x-ray technology to look at the structure of the breast tissue to detect abnormalities such as calcifications, masses, or areas of abnormal tissue pattern.

With a mammogram, radiologists can sometimes see things that aren’t visible on a breast MRI or ultrasound and vice versa. For example, calcifications are sometimes a sign of extremely early disease – and they can often only be detected using a mammogram.

Mammograms are also used during a stereotactic breast biopsy procedure, a test that allows the radiologist to take x-ray images while using a needle to sample a specific area of breast tissue for further evaluation.

Breast MRI – What is it and Who Needs One?

A breast MRI may be an appropriate supplemental screening tool in patients who are determined to have a high lifetime risk of breast cancer, as determined by various risk calculators, most commonly with a risk model known as Tyrer-Cuzick.

The Tyrer-Cuzick method assigns patients with a score that correlates to an average, medium, or high-risk designation. The calculation is based on a wide range of information such as genetic factors including the presence of the BRCA genes, mammographic breast density, detailed family history, age, onset of menses, age of menopause, use of hormone replacement therapy, and age of first live birth.

Even though it’s more ‘sensitive,’ a breast MRI isn’t necessarily ‘better’ and is rarely used by itself. Even for women who are referred for a breast MRI study, experts recommend a yearly mammogram to complement the MRI. In these cases, women should stagger their imaging so they are seen every six months – getting a breast MRI followed by a mammogram just six months later so each woman gets two screenings per year. The information taken from each of these studies will be used together to allow your radiologist to keep a careful watch for any changes that may signal cancerous or precancerous activity.

How does an MRI work? It uses magnetic resonance technology to detect changes in the tissue that may allow the radiologist to diagnose disease before structural changes show up on a mammogram.

Unlike a mammogram and ultrasound which look primarily at the structure of the tissue, MRI studies can also evaluate how the breast tissue is behaving, allowing radiologists to potentially differentiate a cancerous vs a noncancerous mass.

Specifically, MRI allows us to look at blood flow patterns within the breast tissue by using a contrast agent that is injected into the veins. When cancers grow, they recruit blood vessels to feed them due to their rapid growth, so if we see a mass that takes up a lot of the contrast agent (or glows), we may have a higher level of concern for cancer. Conversely, if there is a mass that isn’t taking up any contrast, we understand that this mass may have little cell growth or activity and that it’s likely a non-cancerous mass.

Breast Ultrasound – What is it and Who Needs One?

Breast ultrasound is most commonly used as a complementary imaging test to target specific areas within the breast. For example, if a woman feels a lump or is experiencing breast pain in a specific area, a breast ultrasound may be used in conjunction with a mammogram to look specifically at this region of concern. Or, if a screening mammogram shows an abnormality, your radiologist may call you back in for additional mammogram images and then get a targeted ultrasound of the area in question to get a closer look.

How does a breast ultrasound work? Ultrasound technology sends sound waves through your breast and converts them to images that can help radiologists study various properties of the tissue and of any masses. They are often used to help determine whether a mass felt by the patient or seen by the radiologist might be a fluid-filled cyst or a solid mass.

Breast ultrasounds can also be used to help guide a biopsy. Known as an ultrasound-guided breast biopsy, the radiologist will use ultrasound technology to precisely visualize their needle as they sample a specific area of breast tissue for further evaluation.

In conclusion, each imaging study provides a range of information to your radiologist, to aid them in the early diagnosis of breast cancer and breast conditions. The determination of which tools should be used is a decision made best by your OB/GYN and/or primary doctor who will work with your radiologist to determine the best imaging approach specifically for you.

About the Author

Laura Thomas, MD is a Breast Interventional Radiologist at Raleigh Radiology.
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