Mammography is a specialised form of X-ray imaging designed for the detection and diagnosis of breast disease, particularly early-stage carcinoma.

It requires a finely optimised balance between high spatial resolution, excellent soft-tissue contrast, and low radiation dose, since the breast is a radiosensitive organ and the structures of diagnostic interest differ only slightly in attenuation.

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Purpose and clinical role

Primary goal: early detection of breast cancer, often before it becomes palpable.
Secondary applications:
- Diagnostic evaluation of abnormalities detected on screening.
- Pre-operative localisation and interventional guidance.
- Post-surgical and implant assessment.
Typical imaging projections:
- Craniocaudal (CC) and Mediolateral oblique (MLO) for screening.
- Special views (spot compression, magnification, rolled, cleavage) for diagnostic evaluation.

Mammography differs from general radiography in both beam energy range and system design, optimised for the imaging of low-contrast soft tissue rather than bone.

Imaging requirements

Breast imaging demands:

High spatial resolution (up to 10 line pairs/mm) to visualise microcalcifications.
High contrast resolution to detect subtle attenuation differences between glandular and fatty tissue (≈ 1%).
Uniform exposure across variable breast thickness.
Low mean glandular dose (< 2 mGy per standard view).
Consistent image quality across repeated examinations for comparison.

To meet these requirements, mammography systems use dedicated X-ray tubes, filters, geometry, and detectors, all specifically designed for breast tissue imaging.

Differences from general radiography

Feature	General Radiography	Mammography
Tube potential (kVp)	50–120 kVp	25–32 kVp
Target material	Tungsten	Molybdenum, Rhodium, or Tungsten
Filtration	Aluminium (2–3 mm)	Thin Mo, Rh, or Ag (≈ 0.03–0.05 mm)
Focal spot	0.6–1.2 mm	0.1–0.3 mm
Detector	General DR/CR	High-resolution dedicated system
Compression	Not used	Essential for image quality and dose reduction

These differences ensure an X-ray spectrum optimised for the soft-tissue contrast range of breast tissue, where attenuation differences are small and photon energies must be low enough to enhance photoelectric interactions.

Characteristic energy range

Diagnostic mammography operates within an effective photon energy range of 17–23 keV.
This energy range maximises photoelectric contrast between glandular and adipose tissue while keeping dose as low as reasonably achievable.

Achieved through:

Appropriate target material selection (Mo, Rh, or W).
K-edge filtration to narrow the spectrum.
Tube voltage typically between 25–32 kVp.

By tailoring the X-ray spectrum, mammography systems provide high contrast in soft tissue without unnecessary high-energy photon penetration.

Mammography system components

A dedicated mammography unit consists of:

Component	Function
X-ray tube	Specialised target and anode design to generate characteristic X-rays in the optimal energy range.
Filtration assembly	K-edge filters to narrow the energy spectrum.
Compression paddle	Reduces thickness, scatter, and dose; immobilises the breast.
Flat-panel or CR detector	High DQE, small pixel size (≈ 70–100 µm) for high spatial resolution.
Automatic Exposure Control (AEC)	Adjusts exposure to breast thickness and density.
Dedicated geometry	Fixed SID (typically 60–70 cm) and small focal spot for geometric sharpness.

System optimisation principles

Lower kVp enhances contrast but increases dose — balance required.
Compression reduces both dose and motion blur.
Target–filter combinations are selected to optimise photon energy for breast composition:
- Mo/Mo: thin or fatty breasts.
- Mo/Rh or Rh/Rh: thicker or dense breasts.
- W/Rh or W/Ag: high-energy spectra for digital systems.

Key points and exam tips:

Mammography operates at low photon energies (17–23 keV) to maximise soft-tissue contrast.
Dedicated targets and filters are selected to shape the spectrum for photoelectric dominance.
Compression is central to dose reduction and image uniformity.
Spatial resolution and low noise are critical for microcalcification detection.
Mean glandular dose is the primary dose metric.
Common exam question: “Explain how mammography differs from general radiography in terms of X-ray spectrum, image quality, and dose.”

Up next

Next, we will move on to X-ray Production in Mammography, describing how specialised anode materials, anode angles, and tube voltages generate the optimal X-ray spectrum for high-contrast breast imaging.