Which factor primarily affects contrast on an X-ray image?

The factor that primarily affects contrast on an X-ray image is kVp, which stands for kilovoltage peak. The kVp setting controls the quality and penetrating power of the X-ray beam. When the kVp is increased, it results in a higher energy beam that not only penetrates tissues more effectively but also reduces the contrast because more tissues will absorb the radiation uniformly.

In contrast, when the kVp is lower, the X-ray beam is less penetrating, leading to greater variations in the levels of radiation absorption by different tissues. This creates distinct shades of gray on the film, resulting in higher contrast. Therefore, adjusting the kVp allows for the control of contrast in X-ray images, making it a critical factor in diagnostic imaging.

While other factors like mAs (milliamperage-seconds), exposure time, and film type play roles in image brightness and detail, their influence on contrast is secondary compared to that of kVp. MAs primarily affect the quantity of X-rays produced rather than their energy and penetrating power, while film type relates more to the sensitivity of the film rather than the inherent contrast of the image produced by varying energy levels of the X-ray beam.