A mammogram is a specialized X-ray of the breast tissue, used as the primary method for the early detection of breast cancer. This imaging technique looks for subtle changes, such as microcalcifications or masses, that may indicate cancer, often years before a lump can be felt. Advances in medical technology have created different approaches to mammography, all sharing the goal of providing the clearest possible picture of the breast’s internal structure. Understanding these variations helps patients and healthcare providers choose the most appropriate imaging strategy.
Defining the Procedure: Screening Versus Diagnostic
A screening mammogram is a routine examination performed on individuals who have no symptoms or signs of breast disease. This type of exam typically involves two X-ray views of each breast and serves to identify any abnormalities early on.
A diagnostic mammogram is ordered when a patient has a specific symptom, such as a lump, pain, or nipple discharge, or when a previous screening mammogram produced an abnormal or unclear result. This procedure is more focused and involves the radiologist taking additional X-ray views, sometimes including magnified or spot compression images, to closely examine the area of concern. The radiologist often reviews these detailed images while the patient is still present to determine the next steps.
Standard Imaging: Two-Dimensional (2D) Mammography
Traditional mammography, often called two-dimensional (2D) digital mammography, captures a single flat image of the breast tissue using a low-dose X-ray. During the procedure, the breast is compressed between two plates, and images are taken from two angles—usually top-to-bottom and side-to-side. Compression reduces the breast’s thickness and holds the tissue still to ensure a sharp image.
The primary challenge with 2D mammography is that it superimposes all the breast structures onto a single plane. Overlapping normal tissue, like dense glandular and fibrous tissue, can hide a small cancer, leading to a false negative result. Conversely, the overlap can create a shadow that mimics a true abnormality, sometimes resulting in a false alarm and a call-back for additional testing.
Advanced Imaging: Three-Dimensional (3D) Mammography (Tomosynthesis)
The advanced technique, known as three-dimensional (3D) mammography or Digital Breast Tomosynthesis (DBT), addresses the limitations of 2D imaging by providing a layered view of the breast. The DBT machine moves in a small arc over the compressed breast, taking multiple low-dose X-ray images from various angles. A computer then uses these images to reconstruct the breast tissue into thin, millimeter-sized slices.
This reconstruction allows the radiologist to scroll through the breast tissue layer by layer, much like flipping through the pages of a book. By separating the overlapping structures, 3D mammography significantly improves the clarity of the image, making it easier to distinguish between normal tissue and genuine abnormalities. Studies have shown that 3D mammography can increase the rate of cancer detection and decrease the number of patients called back for unnecessary follow-up images. This improved visualization is particularly beneficial for individuals with dense breast tissue, where overlapping tissue and tumors make detection difficult with 2D imaging.
Supplemental Tools Used with Mammography
While mammography is the standard, other imaging tools are often used as supplementary diagnostics when a mammogram result is unclear or for high-risk screening. Breast ultrasound uses sound waves to create images and is frequently employed to investigate a suspicious area found on a mammogram. Ultrasound is highly effective at determining whether a mass is a fluid-filled cyst, which is typically benign, or a solid mass, which may require further investigation like a biopsy.
Breast Magnetic Resonance Imaging (MRI) utilizes a magnetic field and radiofrequency waves to produce detailed images without using X-rays. MRI is not a replacement for a mammogram but is typically reserved for screening individuals who have an elevated risk of breast cancer, such as those with certain genetic mutations or a strong family history. It is also used to assess the extent of cancer after a diagnosis or to clarify uncertain findings from other imaging tests.