The technology of medicine is rapidly changing as the medical community strives to develop advanced imaging equipment and tests in order to diagnose the disease at the earliest possible moment. As a breast radiologist, I have been extremely interested in the development and implementation of 3D mammography- also known as digital breast tomosynthesis (DBT).
In conventional 2D mammography, the breast is compressed in two different positions, producing 4 total images (2 images of each breast). Cancer can have a similar appearance to glandular breast tissue. When all of the breast tissue is overlapping in a two-dimensional image, it is conceivable that cancer may be hidden in the midst of dense glandular tissue. In 3D mammography, each breast is imaged in the same 2 positions but produces 4 images for each breast– two 2D and two 3D images per breast.
3D mammography acquires a series of low-dose images taken in an arc over the breast. These images are then manipulated or reconstructed by a computer software program so that the radiologist can scroll through images of the breast at one-millimeter increments for the 3D images. Depending on the equipment being used at your facility additional 2D images may also be obtained, or the data from the 3D images will be reconstructed into 2D images for a complete examination. Even if additional 2D images are acquired, the total radiation dose is still below the FDA recommended dose limit for mammography.
The main benefit of 3D mammography over 2D mammography is the ability to better separate normal breast tissue from a breast mass. In the illustration, imagine a photograph of a forest. Being familiar with this particular forest, you know there is a cabin in the trees, however, it is not visible on the two-dimensional static image in the midst of the numerous trees. The photograph of the forest is equivalent to a 2D mammogram which is hiding cancer (the cabin) behind the glandular tissue (the trees). Now, instead of looking at the photograph of the forest, you are in the forest and are able to walk through the trees until the cabin becomes visible. This is representative of 3D mammography in which the radiologist is able to scroll through each part of the breast to better differentiate the normal glandular tissue from cancer.
In 2011 the FDA approved 3D mammography for all mammographic clinical indications (this includes screening mammograms for women not currently experiencing breast symptoms as well as to further evaluate new or changing breast symptoms). Unfortunately, due to the high cost of equipment and the reluctance of insurance companies to reimburse for the examination, transitioning to 3D mammography has been slow throughout the United States. However, with an increasing body of research documenting the advantages of 3D mammography when compared to standard 2D mammography, the implementation of 3D mammography in the United States has been gaining momentum, particularly in the last two years.
In my practice I find 3D mammography to be superior to conventional 2D mammography. The following five main points illustrate the specific advantages of 3D mammography as compared to conventional 2D mammography.
A call back is when a woman is asked to return for additional imaging of the breast to further evaluate an abnormality seen on the screening mammogram. The additional imaging of the breast is referred to as diagnostic imaging. Although with 2D mammography less than 10% of women called back for additional imaging will have cancer, many women experience concern and anxiety when asked to return for additional imaging.
According to Haas et al (Radiology 2013 269:3, 694-700), the callback rate with 3D mammography has been reduced by 29.7%.
Fewer diagnostic images when a patient is called back equals less radiation exposure.
Peppard et al (RadioGraphics 2015 35:4, 975-990) evaluated the change in diagnostic images obtained one year after beginning 3D mammography. They reported an overall 32% decrease in the number of additional images obtained. Additionally, 72% of patients called back did not require additional mammogram images to complete the evaluation. I have found similar trends in my practice since implementing 3D mammography. For a woman called back from a 2D mammogram screening exam, evaluating the screening abnormality involves obtaining additional 2D mammogram views and many times a breast ultrasound. However, with 3D mammography, I have found that the additional mammogram images are only helpful in a select few cases, with most patients being sent directly to ultrasound to evaluate the screening abnormality.
Higher cancer detection rate.
Although 2D screening mammography is known to miss 15-20% of cancers, it is currently considered the gold standard screening exam for breast cancer. Peppard et al reports that 16% of invasive breast cancers were not visible on 2D mammography, compared with 3% not visible on 3D mammography. What does this mean? The radiologist reading your screening exam has a much better chance of seeing breast cancer with 3D technology compared with conventional 2D mammography.
Better screening exam for women with dense breast tissue.
As discussed above, dense breast tissue can hide developing cancer that would otherwise be visible on a screening mammogram in a patient with less glandular tissue and more fatty tissue. 3D mammography allows for the radiologist to see small segments of the breast at a time, more effectively finding a small breast cancer surrounded by dense glandular tissue. Fewer false positives (women called back for additional imaging who ultimately do not have cancer) and higher cancer detection rates have been shown with 3D mammography in women with dense breast tissue. Additionally, if you have received a letter notifying you of your dense breast tissue status, in most cases 3D mammography satisfies the recommendation for additional screening in women with dense breast tissue.
Improved visualization of architectural distortion.
Normal breast tissue has a flowing appearance due to the ligaments maintaining the architecture of the breast. When cancer is growing (as well as a few noncancer diagnoses), the normal flowing appearance of the breast tissue is disrupted, resulting in what breast radiologists refer to as architectural distortion. Architectural distortion can be quite subtle, particularly on 2D mammography. According to Durand et al (RadioGraphics 2016 36:2, 311-321), 12-45% of missed breast cancers have been retrospectively noted to be areas of architectural distortion on the 2D screening exam. 47% of women who underwent surgery for architectural distortion were determined to have breast cancer. 3D mammography shows architectural distortion more clearly, including those not visible on 2D mammography.
Although no breast cancer screening test is perfect, 3D mammography is establishing itself as a superior examination to detect breast cancer when compared to conventional 2D mammography. If 3D mammography is available in your area, I encourage you to discuss this article with your physician prior to scheduling your next annual screening mammography appointment.
About Dr. Carrol
Written by Danielle Carroll, M.D.
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