The primary controlling factor(s) of contrast is (are):

• A. mAs, which control the energy of the x-rays produced
• B. kVp, which primarily controls the quantity of x-rays produced at the target
• C. Focal-spot size, which controls the quantity and quality of x-rays produced
• D. kVp and bit depth

Answer: (D)

Contrast in radiographic imaging is driven by beam energy and how finely we can represent grayscale. Kilovoltage peak sets the X-ray beam’s energy, which determines how differently tissues attenuate the beam. Higher energy beams penetrate more uniformly, reducing apparent contrast, while lower energy beams enhance differences in attenuation and increase contrast. In digital systems, bit depth defines how many gray shades can be displayed; more bits per pixel allow finer distinctions between brightness levels, improving contrast resolution. The other factors mainly affect brightness or sharpness rather than contrast itself: mAs changes the number of photons (influencing exposure and noise), and focal-spot size affects sharpness. So the primary controls of image contrast are kilovoltage peak and bit depth.