Which concept describes how x-ray photons are weakened by the presence of bone?

• A. Attenuation
• B. Contrast resolution
• C. MRI
• D. Spatial resolution

Answer: (A)

Attenuation describes the reduction in x-ray photon intensity as it passes through matter, due to absorption and scattering. Bone has higher density and a higher effective atomic number than surrounding tissues, so it attenuates more photons. That greater attenuation means fewer photons reach the detector behind the bone, making bone appear brighter (radiopaque) on the image and creating the contrast between bone and soft tissues. Contrast resolution deals with distinguishing subtle differences in density, MRI is a different imaging modality, and spatial resolution concerns how small a detail can be resolved.