Digital Breast Tomosynthesis (DBT), commonly known as 3D mammography, is an advanced imaging technique that is rapidly becoming the standard of care for breast screening. It offers a clearer, more detailed view of the breast tissue compared to traditional methods. This article explains the mechanics of this technology, how it differs from older screening methods, what to expect during the appointment, and how to understand the results.
How Digital Breast Tomosynthesis Works
DBT operates on the principle of layered imaging, similar to a CT scan. The breast is compressed in the same manner as a conventional exam to ensure tissue separation and reduce radiation dose. The primary difference is that the X-ray tube moves in a slight arc over the compressed breast instead of remaining stationary.
As the tube moves, it captures a series of multiple low-dose projection images from various angles, typically ranging from 9 to 25 separate exposures. This collection of two-dimensional images is then sent to a powerful computer. The computer uses complex algorithms to reconstruct the data into a set of thin, cross-sectional images, sometimes as thin as one millimeter slices.
This reconstruction allows the radiologist to scroll through the breast tissue layer by layer on a high-resolution workstation. The radiologist can “page through” the breast, much like flipping through a book, to examine the entire volume of tissue. This layered approach is why the technique is called “tomosynthesis,” which literally means “imaging in slices.”
Key Differences from Standard 2D Screening
The most significant advantage of 3D mammography over standard 2D digital mammography is its ability to overcome the problem of overlapping tissue. In a traditional 2D image, all breast structures are captured in a single flat picture. This superposition can cause normal tissue to overlap and appear suspicious (a false positive), or obscure a small cancer (a false negative).
By providing multiple thin slices, DBT effectively separates the overlapping structures, allowing for a much clearer visualization of masses and distortions. This separation is particularly beneficial for women with dense breast tissue, where the risk of a hidden cancer is higher. Studies show that adding 3D technology can increase cancer detection rates by 10% to 54% compared to 2D alone.
The ability to see clearly through the tissue layers significantly reduces the rate of false positives. This translates directly to a decrease in patient “callbacks,” the request for a patient to return for additional imaging. Research indicates that DBT can reduce these recall rates by 15% to 59%. While a 3D exam involves taking more images, the radiation dose is comparable to a standard 2D exam in many modern systems.
Preparing for the Exam and What to Expect
Preparing for a 3D mammogram is similar to preparing for a traditional 2D exam. Patients are advised to schedule the appointment during the week after their menstrual period, as breasts are less tender and swollen, which helps minimize discomfort. On the day of the exam, avoid applying any deodorant, antiperspirant, powder, lotion, or cream to the chest or underarm area.
These substances can contain tiny particles that may appear on the X-ray image as white spots, potentially interfering with the correct diagnosis. Wearing a two-piece outfit simplifies the process since the patient only needs to undress from the waist up. The actual procedure is quick and mirrors the experience of a 2D exam, involving a few moments of compression for each breast.
The main physical difference the patient will notice is the slow, sweeping motion of the X-ray tube arm as it moves in an arc overhead. This movement, which lasts only a few seconds per view, is when the multiple images are acquired. Compression is still necessary to spread the tissue and ensure a clear picture, and the technologist will work quickly and efficiently to complete the imaging.
Understanding Your Results and Follow-Up
Following the exam, the multiple images and reconstructed slices are sent to a specialized radiologist for review. The radiologist examines each layer of tissue for signs of abnormality, a process that takes longer than reviewing a single 2D image. You will often receive a formal report within two weeks of your screening.
The results of the mammogram are communicated using the standardized Breast Imaging Reporting and Data System, known as BI-RADS. This system uses a number scale from 0 to 6 to categorize the findings and recommend the next steps. For instance, a score of 1 means the result is negative, and a score of 2 signifies a benign finding.
A “call back” is assigned a BI-RADS score of 0, meaning the image is incomplete or additional evaluation is needed, usually a diagnostic mammogram or ultrasound. While 3D mammography significantly reduces the need for callbacks, they still occur when the radiologist needs clarification. Most callbacks, even with a BI-RADS 0 score, do not ultimately result in a cancer diagnosis; they simply mean more information is required.