Thanks to energetic yearly awareness campaigns and the resilient breast cancer survivors in the community sharing their stories of early detection, most women of screening age know this mantra by heart: Get your mammogram every year, once a year.
But perhaps you or someone you know has been told they need a breast ultrasound or a breast MRI.
What is the purpose of these additional studies? Why have another breast imaging exam if I just had a mammogram?
The short answer: All breast imaging tests are less than perfect, each breast imaging exam provides different information, and all breast imaging studies are complimentary. Like snapping together pieces of a puzzle, the information obtained in each type of test helps illuminate the entire picture, according to the experts at Ackerman Cancer Center.
Understanding the strengths and weaknesses of the various types of breast imaging tests can give you peace of mind during your next exam.
Here’s a rundown of the most common breast imaging tests you may encounter during your next breast health visit, provided by Ackerman:
The Digital Mammogram
The digital mammogram is the gold standard of early breast cancer detection. The exam is a very low-dose X-ray of the breasts performed with each breast in moderate compression. Compression is important because it prevents breast tissue motion during image acquisition and improves contrast between the tissues in the breast.
A standard screening mammogram usually includes at least four pictures, two of each breast.
Some women may need more than four pictures to screen all the breast tissues adequately depending on certain factors like breast size, breast shape, and presence of implants.
- Upsides: Mammograms are the cornerstone, first-line screening tool for early breast cancer detection because they are a quick, cost-efficient way to get a global view of how the breast tissues are organized, and assess for any changes related to early breast cancer. The mammogram is particularly good at finding very early breast cancer in the form of developing calcifications. While no woman ever finds the mammogram a particularly pleasant experience, any discomfort from the exam is usually minimal or mild, and typically only lasts seconds – the length of time required for compression.
- Downsides: Mammograms are less sensitive in the detection of early breast cancer if a woman has dense breast tissue. This is because cancer can hide within areas of dense glandular breast tissue – the so-called “masking effect” of dense breasts. Additionally, some types of breast cancer, particularly lobular cancers, can be challenging to detect on the mammogram.
The “3D” Mammogram, also known as Digital Breast Tomosynthesis (DBT)
A 3D mammogram is an improvement on the traditional mammogram that helps address the problem of dense breast tissue obscuring an underlying breast cancer. A traditional 2D digital mammogram image represents a picture of the breasts as a slab of tissue, while the 3D mammogram parses the traditional slab image into 1mm-thin slices.
To patients, getting a 3D mammogram is a nearly identical experience to the traditional mammogram. Compression is still used and multiple pictures are taken, but the mammogram machine moves in an arc while acquiring images. A 2D mammogram image is still necessary for the annual screening exam and can be performed at the same time as the 3D mammogram or derived from the 3D images, a so-called “synthetic” 2D mammogram.
- Upsides: 3D mammograms find more cancers than traditional 2D mammograms. About 2.8 more breast cancers per 1,000 women are found on 3D mammography compared to 2D digital mammography. 3D mammograms also help decrease callbacks from screening by resolving areas of asymmetry on the 2D mammogram that are due to overlapping breast tissues.
- Downsides: Unfortunately, the 3D mammogram is still a mammogram. And all the imperfections of 2D mammograms still apply to 3D mammography, including use of ionizing radiation, challenges visualizing early cancers embedded amongst dense breast tissue, and problems visualizing mammographically subtle cancers like lobular breast cancers or very small non-calcified invasive or in situ ductal carcinomas. Lastly, 3D mammograms aren’t as excellent as 2D mammograms when evaluating breast calcifications.
A breast ultrasound uses sound waves to evaluate the breast tissues, and is most often used in a targeted fashion to examine specific areas of the breast with symptoms such as focal pain or a palpable lump. Ultrasound is also used when there is a mammographic finding requiring more characterization.
Targeted breast ultrasound is performed by a technologist or a breast radiologist while the patient is lying on an exam table. Warm gel is used between the skin of the breast and the handheld ultrasound transducer to facilitate the sending and receiving of sound waves and to allow the transducer to glide across the tissues using gentle pressure.
Most women do not find breast ultrasound painful, but occasionally women note heightened breast sensitivity or mild tenderness during the exam.
- Upsides: No ionizing radiation is used during the ultrasound exam, making it a very safe test. Breast ultrasound is reasonably quick to perform and relatively inexpensive. Breast ultrasound is very helpful to characterize breast masses as solid or cystic, even in women with dense breast tissue. Additionally, if a mass is seen with ultrasound, ultrasound can be used as a tool to assist with breast biopsy. In fact, the majority of breast biopsies are performed using ultrasound to guide biopsy needle placement.
- Downsides: While ultrasound approaches the sensitivity of mammography for the detection of cancers, it can also detect benign (noncancerous) masses in the breast, as well. This would be OK if all benign masses looked friendly, but sometimes even noncancerous masses can look suspicious under sonography, resulting in a recommendation for short-term imaging surveillance or breast biopsy. In fact, women who undergo supplemental screening in a whole-breast ultrasound are up to three times more likely to have a false-positive ultrasound exam resulting in additional follow-up breast imaging tests or a breast biopsy that turns out to be benign. Other downsides of sonography include the limited ability of ultrasound to visualize calcifications, and, like mammography, imperfect visualization of lobular cancers and very early invasive cancers, especially in women who have complex breast tissues containing multiple cystic or solid masses.
Breast MRI (Magnetic Resonance Imaging)
Breast MRI uses magnetic fields and radiofrequency pulses to image both breasts. The exam is always performed using IV gadolinium contrast, and takes about 30 minutes to complete. There is no compression required for breast MRI, but the exam is obtained in the face-down position, while lying on the belly, with the breasts hanging pendulous. Breast MRI exams are not painful, per se, but the test is more laborious to endure because of the face-down positioning, the length of the exam, the need to have a temporary IV for the contrast injection, and the loud MRI environment. Also challenging: It is necessary to remain very still during imaging, as even small amounts of motion can ruin the exam.
- Upsides: Breast MRI is the single-most sensitive and specific breast imaging test available for the detection of early breast cancer. Breast MRI isn’t perfect, but it is nearly so, with a sensitivity of 95% or better for finding breast cancer. This means that if you have a negative breast MRI exam, you are unlikely to have breast cancer. Because of this excellent sensitivity, breast MRI exams are the study of choice for women at elevated lifetime risk for breast cancer who need supplemental breast cancer screening in addition to an annual mammogram. Like ultrasound, the breast MRI does not use any ionizing radiation, and is very safe.
- Downsides: Not everyone can tolerate a breast MRI exam. Women who have implanted medical devices that are not MRI-compatible (for instance, many types of pacemakers), certain types of retained metal in the body, or poor kidney function cannot have an MRI. Some women may struggle with the face-down positioning necessary for the test, or may have feelings of claustrophobia during the exam. Although many insurance plans are covering the cost of breast MRI exams as a supplemental screening study for women at higher-than-average risk for breast cancer, this is not true for every insurance plan, and out-of-pocket cost for this expensive study can be prohibitive.
Women can be empowered by the knowledge that their breast imaging provider may use multiple tools in addition to the traditional mammogram to ensure optimal breast health.
By leveraging the strengths of multiple breast imaging modalities, breast imaging physicians provide patients with the most accurate evaluation possible to rule out the presence of early, curable breast cancer.