What type of radiation interaction mainly provides diagnostic information by representing anatomical structures?

The photoelectric effect is the primary interaction that provides significant diagnostic information in radiographic imaging because it involves the complete absorption of incoming X-ray photons by the tissues in the body. When an X-ray photon is absorbed through the photoelectric effect, it results in the ejection of an inner-shell electron from an atom, leading to the ionization of that atom. This process creates a contrast in the images produced because different tissues have varying atomic number compositions; for example, dense tissues like bone absorb more X-ray photons than softer tissues, making them appear lighter on an X-ray image.

This differential absorption allows radiologists to visualize anatomical structures clearly, identifying both normal and pathological conditions based on the variations in density and composition of different tissues. The resultant image thus provides crucial diagnostic information essential for clinical decision-making.

Other interactions such as Compton scattering also contribute to image formation but are less specific in representing anatomical structures, as they can result in scattered photons that degrade image quality. Thermal radiation is not relevant in the context of radiographic imaging, and pair production requires very high-energy photons, which are not typically encountered in routine diagnostic imaging.