Which interaction with matter is known to reduce contrast in an x-ray image?

Compton scattering is the correct answer because it involves the scattering of x-ray photons by electrons in matter, which results in a loss of energy and a change in direction of the x-ray photon. This process increases the amount of scattered radiation that reaches the detector, which can lead to a reduction in image contrast. In simpler terms, when Compton scattering occurs, the x-rays that might have contributed to a clearer distinction between structures in the image are instead scattered, causing a more uniform exposure that diminishes the contrast between different tissues or materials.

In comparison, the photoelectric effect contributes to image contrast by allowing for greater absorption of x-ray photons in areas with higher atomic numbers, which makes those areas appear lighter on the final image. Rayleigh scattering, although it can affect image quality, is less significant in terms of clinical x-ray imaging compared to Compton scattering. Characteristic radiation is primarily the result of interactions within the x-ray tube and does not directly relate to how photons interact with matter in a patient during an x-ray examination. Therefore, while all these interactions have different implications in imaging, Compton scattering is specifically associated with reducing contrast.