How does decreasing the window width affect the contrast of a CT image?

Decreasing the window width in CT imaging refers to a reduction in the range of Hounsfield units displayed in the image. This action causes a visual amplification of the difference in attenuation between adjacent tissues or structures. When the window width is narrower, the display histogram is concentrated on a smaller range of values, which means that slight differences in tissue density are enhanced.

As a result, soft tissues that might have only minimal differences in density can appear with more noticeable contrast against one another. For example, in a narrower window setting, the distinction between gray and white matter in the brain becomes clearer because only a specific, limited range of densities is represented, showcasing those differences more distinctly.

This alteration in contrast is essential in diagnostic imaging, as it can facilitate the identification of pathological changes, such as tumors or lesions, which may not be as clearly visualized with a broader window width, where the densities are averaged out and differences may be less perceptible. Thus, decreasing the window width increases the contrast in a CT image, making it easier for radiologists and clinicians to interpret the images effectively.