CAMRT Radiography Practice Exam

Changing the slope of the look-up table (LUT) graph impacts:

1. Exposure time

2. Contrast

3. Image brightness

4. Patient dose

The correct answer is: Contrast

The choice of contrast as the correct answer relates to how the slope of the look-up table (LUT) graph directly influences the differences in shades of gray in an image. The LUT serves as a function that maps the input pixel values (raw data) from the digital receptor to output pixel values (the displayed image). When the slope of the LUT is increased, this causes a steeper transition between different pixel values, leading to a greater distinction between the lighter and darker areas of the image. Consequently, the image will exhibit higher contrast because the range of brightness levels is expanded, making it easier to distinguish between various tissues or structures in the radiograph. In contrast, a shallower slope would produce lower contrast, where the shades of gray are closer together, making it difficult to differentiate between different tissues. This relationship underlines the importance of the LUT in image processing and the visual interpretation of radiographic images in terms of contrast. While changes to exposure time, image brightness, or patient dose can affect the quality of an image, they operate through different mechanisms. The LUT specifically manipulates the processing of existing pixel data to enhance the perceived contrast in an image, which is why it is the most relevant factor in this context.