What does subject contrast in radiography refer to?

Subject contrast in radiography refers to the magnitude of signal difference in the remnant beam after it passes through the patient. This distinction arises because various tissues absorb x-rays differently, depending on their atomic composition and density. As a result, some areas of the radiographic image will have higher levels of radiographic density (appear darker) while others will have lower levels (appear lighter). This contrast enables the visualization of different structures and pathologies within the body.

While brightness levels are influenced by subject contrast, they do not define it. Similarly, detail resolution pertains to the film's ability to portray fine structures, which is also not the same as subject contrast. Exposure time affects the overall density of the image, but it does not directly relate to the inherent differences in x-ray absorption by various tissues. Therefore, the best definition of subject contrast is grounded in the variations in signal differences within the remnant beam post-interaction with the patient.