What happens to image quality when the kVp is adjusted from 90 to 70 and other factors remain unchanged?

When the kilovolt peak (kVp) is adjusted, it directly affects the penetration power of the X-ray beam. Lowering the kVp from 90 to 70 reduces the energy of the X-rays, resulting in several significant changes in image quality.

As kVp decreases, the X-ray beam becomes less penetrating. This leads to a decrease in overall density (the blackness of the image), as fewer X-rays reach the film or detector. In terms of contrast, which is the difference in density between different structures in the image, reducing the kVp typically increases contrast. This happens because lower-energy X-rays are absorbed more by denser tissues and structures, creating a sharper distinction between different types of tissues in the image.

Thus, the correct response indicates that density decreases due to a lower quantity of X-rays reaching the detector, while contrast increases due to the enhanced differentiation among various tissue densities. This combination of increased contrast and decreased density aligns with the established principles of radiographic imaging.