Mammography: Breast Cancer Screening and Diagnosis

Mammography is the primary imaging modality used to screen for and diagnose breast cancer, employing low-dose X-ray technology to produce detailed images of breast tissue. This page covers how mammography works, the regulatory framework governing its use, the distinction between screening and diagnostic applications, and the evidence-based thresholds that guide clinical decision-making. Breast cancer remains the second most common cancer diagnosis among women in the United States (National Cancer Institute), making mammography one of the most consequential and widely regulated imaging examinations in radiology.

Definition and scope

Mammography is an X-ray-based imaging examination of the breast, regulated under federal law by the Mammography Quality Standards Act (MQSA), which requires all mammography facilities operating in the United States to be certified by the FDA. The MQSA, enacted in 1992 and enforced through ongoing facility inspections, sets minimum standards for equipment, personnel qualifications, and quality assurance protocols. Facilities that fail inspection can be subject to sanctions ranging from corrective action plans to full closure.

The scope of mammography encompasses two principal applications:

A third application, breast tomosynthesis (also called 3D mammography), generates multiple thin-slice X-ray images through the breast at different angles, which are reconstructed into a three-dimensional dataset. The FDA has cleared tomosynthesis as a mammographic technology, and it is now offered alongside conventional 2D digital mammography at certified facilities.

Mammography is situated within a broader landscape of breast imaging that includes ultrasound and MRI; the how medical imaging works page provides a foundational overview of how these modalities differ mechanically.

How it works

During a mammographic examination, the breast is positioned on a flat receptor plate and compressed by a paddle. Compression serves two purposes: it reduces tissue thickness to lower radiation dose, and it separates overlapping structures to improve lesion conspicuity. The compression force typically ranges from 111 to 200 Newtons, as specified in MQSA equipment standards (FDA MQSA).

X-rays are generated at tube voltages typically between 25 and 35 kilovolts (kVp) — considerably lower than chest or abdominal radiography — using molybdenum, rhodium, or tungsten target/filter combinations optimized for breast tissue contrast. The average glandular dose per standard two-view screening examination is approximately 3 to 4 milligray (mGy) (FDA, MQSA National Statistics), which falls within accepted safety parameters outlined in the ACR (American College of Radiology) Mammography Accreditation Program.

Digital detectors — either full-field digital mammography (FFDM) or digital breast tomosynthesis (DBT) detectors — have largely replaced film-screen systems in certified U.S. facilities. Images are interpreted by radiologists who hold credentials meeting MQSA interpreter requirements: a minimum of 60 mammographic interpretation hours of training and at least 960 examinations read in a 24-month period.

Radiologists document findings using the ACR BI-RADS® (Breast Imaging Reporting and Data System) lexicon, a standardized classification framework published by the American College of Radiology. BI-RADS assigns a category from 0 to 6 to each examination, with explicit management recommendations tied to each category.

Common scenarios

Routine annual screening: The most common mammography scenario involves asymptomatic individuals presenting for scheduled screening. Standard positioning includes craniocaudal (CC) and mediolateral oblique (MLO) views of each breast — four images total for a bilateral examination.

Callback for additional imaging: A BI-RADS 0 (incomplete) assessment triggers a callback for additional evaluation. Approximately 10% of screening mammograms result in a callback, according to the American Cancer Society, though the majority of callbacks do not result in a cancer diagnosis.

Diagnostic workup: When a patient presents with a specific symptom, diagnostic mammography is performed under direct radiologist supervision, often with real-time additional views (spot compression, magnification) tailored to the area of concern.

Short-interval follow-up: A BI-RADS 3 (probably benign) finding carries an estimated malignancy risk of less than 2% (ACR BI-RADS Atlas, 5th Edition) and typically warrants a 6-month follow-up examination rather than immediate biopsy.

Image-guided biopsy: Suspicious findings classified as BI-RADS 4 or 5 require tissue sampling. Mammography-guided (stereotactic) core needle biopsy is one of the percutaneous methods available; the image-guided biopsy page details biopsy techniques across modalities.

Decision boundaries

Determining when to perform mammography, and at what frequency, involves formal guideline thresholds that differ across major professional bodies:

  1. U.S. Preventive Services Task Force (USPSTF): Recommends biennial screening for average-risk individuals starting at age 40 (USPSTF, 2024 Final Recommendation).
  2. American Cancer Society: Recommends annual screening beginning at age 45, with the option to begin at 40, transitioning to biennial screening at age 55 (ACS Guidelines, 2015).
  3. American College of Radiology / Society of Breast Imaging: Recommends annual screening beginning at age 40 for average-risk individuals.

High-risk individuals — defined by factors including BRCA1/BRCA2 pathogenic variants, a first-degree relative with a known mutation, or a lifetime breast cancer risk of 20% or greater calculated by an accepted risk model — may qualify for supplemental MRI screening, as specified in ACR Appropriateness Criteria.

The BI-RADS 4 category is subdivided into 4A (low suspicion, estimated malignancy risk 2–10%), 4B (moderate suspicion, 10–50%), and 4C (high suspicion, 50–95%), providing radiologists and referring clinicians a gradient for prioritizing biopsy urgency.

Mammography is not applied uniformly across all symptomatic presentations. Individuals under age 30 with a palpable mass are typically evaluated first with ultrasound rather than mammography due to breast tissue density patterns in younger populations. Dense breast tissue — classified under the ACR four-category density scale — reduces mammographic sensitivity and is now subject to federal notification requirements under the Dense Breast Notification Law, effective since 2024.

The regulatory context for radiology page documents the broader federal and state-level compliance framework within which mammography facilities must operate, including MQSA inspection cycles and ACR accreditation requirements.

Facilities, screening intervals, and appropriate supplemental imaging are also discussed within the cancer screening surveillance imaging section of this reference network, which situates mammography alongside CT lung cancer screening and other population-level imaging programs.

For a structured overview of all imaging modalities and their clinical applications, the radiology authority index provides a navigable entry point to this reference network.

References

The law belongs to the people. Georgia v. Public.Resource.Org, 590 U.S. (2020)