What is the mechanism of mammography in breast cancer screening?

How Mammography Works

Mammography uses low-dose X-rays to create images of breast tissue by detecting differences in tissue density—dense fibroglandular tissue and cancers appear white, while fatty tissue appears dark, allowing radiologists to identify suspicious masses, calcifications, or architectural distortions that may indicate breast cancer. 1

Basic Physical Principles

• X-ray absorption: Mammography relies on differential X-ray absorption by different breast tissues—glandular tissue, fat, and potential tumors absorb X-rays at different rates, creating contrast on the image 1, 2
• Standard technique: A screening mammogram involves compressing the breast between two plates and taking two X-ray images of each breast: one from the top (craniocaudal view) and one from the side (mediolateral oblique view) 1
• Compression purpose: Breast compression reduces tissue thickness, spreads overlapping structures, decreases radiation dose, and minimizes motion blur to improve image quality 1
• Radiation dose: Modern mammography delivers a mean glandular dose of approximately 1.9 mGy per view, which is considered low-dose and poses minimal measurable risk 2, 3

Image Interpretation and Detection

• Visual appearance: Cancers typically appear as white masses, clusters of microcalcifications, or areas of architectural distortion on mammograms 1, 4
• Density challenge: Both normal dense fibroglandular tissue and cancers appear white on mammography, making cancer detection difficult in women with dense breasts—sensitivity drops from 87% in fatty breasts to as low as 30-63% in extremely dense breasts 1, 4
• Detection sensitivity: Overall mammographic sensitivity for breast cancer is approximately 75% in average-risk women, but only 50% in women with heterogeneously dense tissue 1

Modern Technological Advances

Digital Breast Tomosynthesis (DBT)

• Mechanism: DBT acquires multiple low-dose X-ray images as the X-ray tube moves in an arc around the breast, then reconstructs these into thin-section 2D images that reduce summation shadows and overlapping structures 1
• Improved detection: DBT increases cancer detection rates by 1.7-2.27 per 1,000 screened women compared to standard 2D mammography, with detected cancers tending to be smaller, lymph node-negative, and less biologically aggressive 1
• Reduced false positives: DBT decreases recall rates by 15-63% compared to standard mammography by revealing the true nature of potential false-positive findings without additional imaging 1, 4

Digital vs. Film Mammography

• Digital advantages: Digital mammography generates electronic images that allow computer storage, manipulation, image transmission, and improved detection in younger women with dense breasts 1
• Equivalent overall accuracy: Large-scale trials show no difference in overall accuracy between digital and film mammography, though digital performs significantly better in women under 50 with dense breasts 1

Clinical Application and Reporting

• BI-RADS classification: Mammographic results are reported using standardized Breast Imaging Reporting and Data System (BI-RADS) categories 1-6, which classify likelihood of malignancy and provide management recommendations 1
• Double reading: Independent review by two radiologists increases screening sensitivity by 5-15% and is recommended in screening programs 1
• Quality standards: Mammographic equipment must produce low-dose, high-quality examinations subject to regular quality control testing, and radiologists should read a minimum of 5,000 mammograms annually to maintain proficiency 1

Limitations and Supplemental Imaging

• Dense breast limitation: Mammography sensitivity decreases by 30-48% in extremely dense tissue, where both normal tissue and cancers appear white 1, 4
• Supplemental screening: Women with extremely dense breasts benefit from supplemental MRI screening, which demonstrates 81-100% sensitivity and detects an additional 16.5 cancers per 1,000 screened 1, 4
• Mortality benefit: Screening mammography reduces breast cancer mortality by approximately 30-40% through early detection of cancers before they become clinically apparent 1, 2