A mammogram is a specialized X-ray imaging procedure designed to capture detailed pictures of the internal structures of the breast. Using low-dose radiation, the technique helps healthcare providers visualize tissue and detect abnormalities not noticeable during a physical examination. The specific type of mammogram received depends on symptoms, medical history, and the technology available.
Defining the Exam by Purpose
The most fundamental way to categorize a mammogram is by the reason for the exam, dividing them into two distinct procedural types. A screening mammogram is intended for women who have no noticeable breast symptoms, such as a lump or pain. This routine, preventative measure is typically performed annually or biennially to look for signs of disease before physical symptoms develop. It is a quick, standard check-up that captures two general views of each breast.
A diagnostic mammogram is a targeted evaluation performed when a patient has a symptom or when a prior screening result was abnormal. This exam is more detailed and focused, often taking longer than a screening exam. The radiologist may use specialized views, such as magnification or spot compression, to closely examine a specific area of concern. This process helps determine the precise size, shape, and location of an abnormality.
The primary goal of the diagnostic procedure is to solve a clinical problem, providing a definitive assessment. If a screening mammogram detects something suspicious, a diagnostic exam determines if the finding is benign or requires a biopsy. Diagnostic results are frequently available to the patient before they leave the clinic, unlike the standard timeline for screening results.
Standard Imaging Technology (2D vs. 3D)
Mammograms are defined by the imaging technology used to create the pictures. The traditional method is two-dimensional (2D) digital mammography, which captures a single, flat image of the entire breast from each angle. This technique successfully detects tumors and calcifications. However, a limitation of 2D imaging is that all layers of breast tissue are superimposed onto one picture.
This tissue overlap can hide small cancers, especially in women with dense breast tissue, which appears white on the image, similar to cancerous masses. Overlapping shadows can also mimic a true abnormality, leading to unnecessary callbacks for additional testing. The digital image allows for easy storage and electronic review by the radiologist.
A more advanced technology is three-dimensional (3D) mammography, also known as Digital Breast Tomosynthesis (DBT). This has become a common standard of care. During a DBT exam, the X-ray tube moves in an arc over the compressed breast, capturing many thin image slices from different angles. A computer reconstructs these slices into a volume of data, allowing the radiologist to scroll through the breast tissue layer by layer.
Looking at these thin cross-sections significantly reduces the effect of tissue overlap, which is particularly beneficial for women with dense breasts. Studies show that 3D mammography detects a greater number of cancers than 2D imaging alone, often finding them at an earlier stage. This improved clarity also results in fewer patients being called back for follow-up imaging, reducing anxiety and cost.
Specialized Diagnostic Techniques
When standard 2D or 3D mammography is inconclusive or for high-risk women, specialized techniques provide a more detailed diagnosis. Contrast-Enhanced Mammography (CEM) involves injecting an iodine-based dye into a vein before X-ray images are taken. The dye highlights areas of increased blood flow, a characteristic feature of rapidly growing tumors, which tend to develop more permeable blood vessels.
This functional imaging technique is less affected by breast density and offers high sensitivity, often comparable to magnetic resonance imaging (MRI). CEM can evaluate suspicious findings from a conventional mammogram or determine the extent of a known cancer. It is sometimes used as an alternative for patients who cannot undergo an MRI due to claustrophobia or implanted devices.
Another specialized approach is Molecular Breast Imaging (MBI), which uses a radioactive tracer injected into the bloodstream. This tracer is preferentially taken up by highly metabolically active cells, such as cancer cells. A specialized gamma camera detects the radiation emitted by the tracer, creating a functional map of the breast.
Like CEM, MBI is not limited by breast tissue density, making it a valuable tool for women where a standard mammogram may be challenging to interpret. MBI is used for further evaluation of an abnormality or as a supplemental screening method alongside a conventional mammogram for high-risk patients.