Mammography is a medical imaging technology designed to find signs of breast cancer using low-dose X-rays. It is important because small tumors or tiny calcium deposits can sometimes be seen before they can be felt. The breast is gently compressed to spread tissue into a thinner, more uniform layer for clearer imaging.
Modern systems use digital detectors to produce high-contrast images while keeping radiation exposure low.
During an exam, an X-ray tube sends a controlled beam through the compressed breast toward a detector. Different tissues absorb X-rays by different amounts, creating contrast that can reveal masses, calcifications, or tissue distortion. Digital breast tomosynthesis takes many low-dose images from slightly different angles and reconstructs thin slices of the breast.
This helps reduce the problem of overlapping tissue and can improve detection in dense breasts.
Key Facts
- X-ray photon energy is given by E = hf, where h is Planck's constant and f is frequency.
- X-ray intensity after passing through tissue follows I = I0e^(-μx), where μ is the attenuation coefficient and x is thickness.
- Compression reduces tissue thickness x, which can improve image sharpness and reduce the dose needed for a useful image.
- Mammography commonly uses low-energy X-rays, often about 20 to 40 keV, to create strong contrast in soft tissue.
- Digital detectors convert absorbed X-ray energy into electrical signals that are processed into an image.
- Digital tomosynthesis records projections at multiple angles and reconstructs slice images to reduce tissue overlap.
Vocabulary
- Mammography
- Mammography is a breast imaging method that uses low-dose X-rays to look for changes such as masses or calcifications.
- Compression paddle
- A compression paddle is the clear plate that gently presses the breast to make tissue thinner and more evenly spread.
- Attenuation
- Attenuation is the reduction of X-ray intensity as photons are absorbed or scattered while passing through matter.
- Digital detector
- A digital detector is an electronic sensor that records transmitted X-rays and converts them into image data.
- Digital tomosynthesis
- Digital tomosynthesis is a 3D-like mammography method that reconstructs thin image slices from many low-dose X-ray views.
Common Mistakes to Avoid
- Thinking compression is only for patient positioning. This is wrong because compression also reduces tissue thickness, lowers motion blur, improves contrast, and can reduce the dose needed for a clear image.
- Assuming more radiation always gives a better mammogram. This is wrong because image quality must be balanced with patient safety, and modern systems use optimized low-dose exposures with sensitive detectors.
- Confusing a 2D mammogram with tomosynthesis. This is wrong because a 2D mammogram records a small number of flat projection images, while tomosynthesis uses many angles to reconstruct thin slices.
- Ignoring tissue overlap when interpreting images. This is wrong because overlapping normal tissue can hide a lesion or mimic one, which is one reason tomosynthesis can be helpful.
Practice Questions
- 1 An X-ray beam has initial intensity I0 = 100 units and passes through breast tissue with μ = 0.12 cm^-1 and x = 5.0 cm. Using I = I0e^(-μx), calculate the transmitted intensity.
- 2 Compression reduces breast thickness from 6.0 cm to 4.0 cm. If μ = 0.10 cm^-1 and I0 stays the same, calculate the ratio of transmitted intensity after compression to transmitted intensity before compression.
- 3 Explain why compressing the breast can improve a mammogram even though it may be uncomfortable for a short time. Include at least two physical reasons.