What is the name of the process by which an X-ray beam is reduced in intensity by absorption and scattering as it passes through matter?

• A. Attenuation
• B. Absorption
• C. Scattering
• D. Filtration

Answer: (A)

Attenuation is the name for the decrease in X-ray beam intensity as it passes through matter. This happens because photons are either absorbed by the atoms or scattered out of the beam. Absorption removes photons entirely, transferring their energy to the material, while scattering redirects photons away from the original beam path (for example, Compton and coherent scattering). The remaining photons that continue toward the image receptor produce the transmitted beam, with intensity that decreases approximately according to I = I0 e^{-μx}, where μ depends on the material’s density, atomic number, and the photon energy. In diagnostic radiography, the main contributors are photoelectric absorption and Compton scattering, both of which reduce beam intensity. Filtration is a separate technique that uses a material to remove low-energy photons before they reach the patient or detector, but it’s not the general process of attenuation itself. So, the term that best describes the described process is attenuation.