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Ionising · Breast

Mammography

Using low-energy X-rays to image the soft tissue of the breast with high contrast — the modality subject to some of the strictest quality and dose standards in the world.

Modality profile· ~10 min read· With photos & sources
Mammography unit
A mammography unit: compression paddle, target–filter assembly and detector platform.  Foto: Wikimedia Commons · Public domain

Overview

Mammography is designed specifically to reveal small differences in the soft tissue of the breast (masses, microcalcifications). Because the breast consists largely of soft tissues of similar density, achieving sufficient contrast requires low-energy X-rays and a dedicated detector/technique. This sensitivity makes mammography the principal tool of breast cancer screening.1

How it works

In mammography the typical tube voltage is about 25–35 kVp — very low compared with other X-ray exams, because the goal is to maximize soft-tissue contrast. The beam spectrum is shaped with dedicated target–filter combinations; common options are based on molybdenum, rhodium and tungsten (e.g. Mo/Mo, Mo/Rh, W/Rh).2 These combinations preserve diagnostic contrast without raising dose unnecessarily.

The role of compression

The distinctive step of mammography is compression of the breast with a paddle. Compression does several jobs at once: it reduces tissue thickness (lowering the required dose), spreads tissue to reduce overlap, and limits motion to prevent blur. This both improves image quality and optimizes dose.1

Mean glandular dose (MGD)

Unlike other modalities, dose in mammography is described by the mean glandular dose (MGD), because the most radiosensitive tissue is the glandular component of the breast.2 In the United States, MQSA limits the average glandular dose to 3 mGy per view for a standard phantom.4 Frameworks such as the European/EUREF guidance and the UKHSA NDRL table use acceptance or reference values around 2.5 mGy in standard screening contexts.5

In terms of effective dose, a typical mammography exam is low-dose (commonly reported in the ~0.1–0.4 mSv range), and the early-detection benefit it provides far outweighs this small dose.3

Example of a mammogram
A typical output: a mammographic image.  Image: Wikimedia Commons · Public domain

Digital mammography and tomosynthesis

Today, film has largely given way to full-field digital mammography (FFDM). A step beyond is digital breast tomosynthesis (DBT, "3D mammography"): the tube moves along a small arc to acquire many low-dose projections, from which thin slices are reconstructed. By reducing the problem of overlapping tissue, tomosynthesis improves lesion detection, especially in dense breasts.1

Tube voltage
~25–35 kVp
Target / filter
Mo, Rh, W Mo/Mo · Mo/Rh · W/Rh
Dose metric
MGD MQSA limit 3 mGy/view (standard phantom)
Advanced
FFDM, tomosynthesis (DBT)

References

  1. U.S. FDA. Mammography & Mammography Quality Standards Act (MQSA). fda.gov · Mammography
  2. Sechopoulos I, et al. Joint AAPM Task Group 282 / EFOMP Working Group Report: Breast dosimetry for standard and advanced mammography. Medical Physics, 2023.
  3. RadiologyInfo.org (RSNA/ACR). Radiation Dose in X-Ray and CT Exams (mammography effective dose). radiologyinfo.org
  4. U.S. FDA. Mammography Quality Standards Act (MQSA), 21 CFR 900 (average glandular dose limit for the standard phantom). eCFR · 21 CFR 900
  5. European Commission / EUREF. European Guidelines for Quality Assurance in Breast Cancer Screening and Diagnosis; UKHSA. National Diagnostic Reference Levels for screening mammography. EUREF protocol · UKHSA NDRL
  6. Images: Mammography machine.jpg & Mammogram.jpg, Wikimedia Commons (public domain).
Note: Dose limits and targets vary by country and body; technical values depend on device and protocol. For clinical and regulatory decisions, consult a qualified medical physicist and current regulations.

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