Which value controls the brightness in a CT image?

In computed tomography (CT) imaging, the value that controls the brightness of the image is known as the window level. The window level determines the center of a range of pixel values that will be displayed, effectively setting the brightness of the image. By adjusting the window level, the operator can increase or decrease the brightness of the image to enhance visibility for diagnostic purposes.

When the window level is set too high, darker areas may become less visible, while a lower setting can make lighter structures more prominent. This is critical for ensuring that the various anatomical structures within the body are clearly defined and can be accurately assessed.

While window width affects the contrast and the range of densities displayed, it does not directly control brightness. The contrast ratio is a measure of the difference in luminance or color that makes an object distinguishable, and the brightness index typically refers to a numerical representation of brightness but is not used as a direct control in image adjustment. Thus, the window level serves as the key parameter for manipulating image brightness effectively.