Final answer:
The difference between the shades of gray in the context of radiation exposure is contrast.
Step-by-step explanation:
The difference between the shades of gray in the context of radiation exposure is contrast. Contrast refers to the difference in brightness between different areas of an image. In medical imaging, contrast is important for distinguishing different tissues or structures. In the case of X-ray images, areas with higher density, such as bones, appear whiter, while areas with lower density, such as soft tissues, appear darker.