What is the relationship between kilovoltage and subject contrast?

In diagnostic imaging, kilovoltage (kV) is a crucial factor that influences the quality of the resulting images. Specifically, increased kilovoltage reduces subject contrast in images. This occurs because high kilovoltage settings produce x-rays with greater energy levels, resulting in a more uniform penetration capability through various tissues. As a result, different anatomical structures become less distinct in their radiographic representations, leading to decreased subject contrast.

Subject contrast refers to the differences in optical density among various tissues in the image. Lower contrast means that the shades of gray between tissues are closer together, making it harder to differentiate between them. When kilovoltage is increased, the x-rays are less attenuated by lower-density tissues such as fat and muscle, diminishing the variations in intensity seen on the image.

In summary, the relationship between increased kilovoltage and reduced subject contrast is foundational in radiographic technique, as it highlights the need for careful selection of exposure settings to balance image quality and diagnostic usefulness.