The term "dynamic range" in digital radiography refers to:

Dynamic range in digital radiography is primarily concerned with the range of exposure values that the imaging system can accurately capture and display. This means it defines how well the system can detect and represent different levels of radiation exposure, which is crucial for producing images that have sufficient detail and contrast.

When a digital radiography system has a wide dynamic range, it is able to accommodate a broad spectrum of exposure levels, from very low to very high. This ability is important in ensuring that both underexposed and overexposed areas of an image can be visualized clearly without significant loss of detail or loss of image information.

The definition of dynamic range closely ties to the quality of the diagnostic images produced, impacting the clinician's ability to make accurate diagnoses based on these images. Systems with limited dynamic ranges might result in poor image quality where critical structures may be obscured or indistinguishable.

In contrast, the other options refer to aspects of radiography that do not define dynamic range directly. For instance, pixel sizes relate more to the resolution of the image, the number of image files speaks to storage capacity, and contrast levels are about the difference between shades in an image rather than the ability of the system to detect those shades over a range of exposures.