What is the primary interaction responsible for image contrast in radiographs?

The primary interaction responsible for image contrast in radiographs is the photoelectric effect. This interaction occurs when X-ray photons are absorbed by the tissues in the body, specifically when they transfer enough energy to an inner-shell electron of an atom in the tissue, resulting in the electron being ejected from its orbit.

The significance of the photoelectric effect in radiography lies in its dependence on the atomic number of the tissue being imaged and the energy of the incident photons. Tissues with higher atomic numbers, like bone, have a greater probability of absorbing X-rays through the photoelectric effect compared to lower atomic number tissues, such as muscles or fat. This differential absorption creates the contrast seen on the radiograph—the denser structures appear lighter (more opaque) because they absorb more radiation, while less dense structures appear darker due to fewer X-rays being absorbed.

Other interactions play roles in imaging, but they primarily contribute to either reducing overall image quality or producing unwanted noise rather than enhancing contrast. The Compton effect, which involves the scattering of X-ray photons and results in reduced image quality, doesn't contribute as effectively to contrast as the photoelectric effect does. Scatter radiation is a byproduct of other interactions, like the Compton effect, and mainly affects image