Final answer:
A high kVp leads to lower contrast in x-ray images because it allows more x-ray photons to penetrate tissues, making the differences between densities less distinct.
Step-by-step explanation:
A high kilovoltage peak (kVp) in x-ray imaging results in lower contrast because the increased energy allows more x-ray photons to penetrate different densities of tissue. This increased penetration reduces the differences in the absorption of x-rays between soft and hard tissues, leading to a more uniform image that has less contrast between these structures. With a lower kVp, there's a greater variance in x-ray absorption, making the differences in tissue density more pronounced and thereby increasing the image contrast. High kVp is typically used to image denser structures, like a leg in a cast, while lower kVp can be sufficient for less dense areas, such as a chest x-ray.