A Breast Imaging Primer: Mammos and Sonos and MR’s, Oh My!
Thanks to energetic yearly awareness campaigns and the resilient breast cancer survivors 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’s that all about? What is the purpose of these additional tests? Why have another breast imaging study if I just had a mammogram? The short answer is that all breast imaging tests are imperfect. Each test provides different information and they are all complimentary. Like snapping together pieces of a puzzle, the information obtained in each type of test helps define the overall picture.
Understanding the strengths and weaknesses of the various types of breast imaging tests can give you peace of mind during your next exam. With this goal in mind, I want to empower you with this primer of key information about the cornerstone breast imaging tests you are most likely to encounter during your next breast health visit.
The Traditional Mammogram
A mammogram is basically a very low-dose x-ray of the breast tissues. This is performed with each breast in moderate compression. Compression is used to prevent breast tissue motion during the image and to improve the contrast between the fibroglandular and the fatty tissues that are present in the breasts of all women. A standard screening mammogram usually includes four total 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 fairly quick, cost-efficient way to get a global view of how the breast tissues are organized and assess for changes from year to year that might indicate development of early breast cancer. The mammogram is particularly good at finding very early cancers that show up as 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 – basically the length of time required for compression.
- Downsides: Mammograms are less sensitive for changes related to early breast cancer if a person has dense breast tissue. This is because early cancers can hide within areas of dense glandular breast tissue – the so-called “masking effect” of dense breast tissue. Additionally, some types of breast cancer, particularly lobular cancers, can be mammographically occult, meaning they do not show up well on the mammogram. Mammograms also use ionizing radiation to create the image
The New Mammogram also known as Digital Breast Tomosynthesis (DBT) or “3D” Mammogram
A 3D mammogram is an improvement on the traditional mammogram that helps address the problem of overlapping tissues masking an underlying cancer. A traditional mammogram image represents a picture of the breasts as a slab of tissue while the 3D mammogram breaks up the traditional slab image into 1mm thick slices. The patient experience of getting a 3D mammogram is nearly identical to the traditional mammogram. Compression is still used and multiple pictures 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 a composite of 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 1000 women are found on 3D mammography compared to 2D mammography. 3D mammograms also help decrease callbacks from screening by resolving 2D mammographic asymmetries due to overlapping breast tissues. More cancers found and less diagnostic mammograms required, what’s not to love?
- Downsides: Unfortunately the 3D mammogram is still, well, a mammogram. All the imperfections of 2D mammograms still apply to the 3D variety including the use of ionizing radiation, difficulty visualizing early cancers embedded among dense breast tissue, and problems identifying mammographically subtle pathologies like lobular cancers or very small non-calcified invasive or in situ ductal carcinomas. 3D mammograms aren’t as good as 2D mammograms when it comes to visualization of calcifications.
A breast ultrasound uses sound waves to evaluate the breast tissues and is most often used in a targeted fashion to evaluate a specific area or areas of the breast where a patient has symptoms, such as pain or a palpable lump or where there is a mammographic finding requiring more in-depth characterization. Targeted breast ultrasound is performed by a technologist and/or breast radiologist with the patient lying down 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 do report heightened breast sensitivity or mild tenderness during the exam.
- Upsides: No ionizing radiation is used during the ultrasound exam, making it a very safe study. Breast ultrasound is also reasonably quick to perform and fairly inexpensive. One of the biggest benefits of breast ultrasound is that it is often able to detect breast masses and characterize them as solid or cystic, even in women with dense breast tissue. Additionally, if a mass is found with ultrasound, ultrasound can be used as a tool to guide breast biopsy. The majority of breast biopsies are, in fact, 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 masses in the breast as well. This would be fine if all benign masses looked friendly, but sometimes benign masses can look indeterminate or suspicious by sonography, resulting in a recommendation for imaging surveillance or breast biopsy. In fact, women who undergo supplemental screening 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 recommendation for a breast mass that, in the end, 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 where there is a background of multiple bilateral solid and cystic 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 completed in the face-down position, while lying on your belly, with the breasts hanging down from the chest. Breast MRI exams are not painful per se, but the whole 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. What is also challenging is the necessity to maintain absolute stillness 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, it’s a strong negative, and you are highly 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 requiring 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’s as this test is more widely utilized, this is not true of every insurance plan, and out-of-pocket cost for this expensive study can be prohibitive.
It is my hope that our readers may take the pearls in this primer to their next breast imaging appointment, empowered by the knowledge that their breast imaging provider may use multiple tools in addition to the mammogram, leveraging the strength of each type of study to render the most accurate evaluation possible for the detection of early, treatable breast cancer. As always, please don’t hesitate to reach out to me or to our team with questions.