The principal controlling factor of radiographic contrast when using film-screen technology?

• A. Source-to-image distance
• B. Exposure time
• C. kVp
• D. mA

Answer: (C)

The main thing that sets how much contrast you see in a film-screen radiograph is the energy of the X-ray beam, controlled by kilovoltage peak (kVp). Lower kVp produces photons with less penetrating power, so tissues with different densities (like bone vs. soft tissue) attenuate the beam more differently, giving higher subject contrast on the film. Higher kVp makes the beam more penetrating, reducing those differential attenuations and resulting in a more uniform, gray appearance (lower contrast). The film-screen system then converts that attenuation pattern into the visible grayscale, while factors like source-to-image distance or exposure time mainly affect overall image density (how dark or light the film is) rather than the contrast between tissues.