Which windowing option will produce the longest scale of contrast for a CT image of the abdomen?

The chosen option utilizes a window width of 900, which is significant in achieving a long scale of contrast in CT imaging of the abdomen. A wider window width allows for more shades of grey to be displayed in the image, which translates to a greater range of tissue densities being visualized. This is particularly beneficial in abdominal imaging where differentiation between various soft tissues, fat, fluid, and possibly pathology is crucial.

With a window level set at 40, the midpoint of the window remains well positioned for assessing tissues and structures typically present in the abdomen. The combination of a wide window width and an appropriate window level effectively enhances the ability to visualize subtle differences in tissue contrast.

In contrast, narrower window widths would limit the range of greyscale displayed, thus compressing the contrast and reducing the ability to distinguish between adjacent tissues. Therefore, utilizing a window width of 900 optimizes the visibility of structures within the CT image, providing the longest scale of contrast for detailed assessment.