Which of the following factors primarily affects the contrast of an x-ray image?

The factor that primarily affects the contrast of an x-ray image is the kVp (kilovolt peak) setting. The kVp determines the quality and energy of the x-ray photons produced. A higher kVp results in x-rays with higher energy, which penetrate tissues more effectively, leading to fewer differences in the absorption of x-rays between different tissues. This results in lower contrast images because structures with varying densities may appear more similar in shades of gray.

Conversely, a lower kVp produces lower energy x-rays, which are less penetrating and result in greater differences in absorption. This can enhance the contrast, allowing for better differentiation between structures of varying densities. Therefore, adjusting the kVp allows radiologic technologists to control the contrast of the image effectively, making it a crucial factor in producing diagnostic-quality radiographs.