What effect does decreasing SID have on image sharpness?

Decreasing the source-to-image distance (SID) has a direct impact on image sharpness, leading to a decrease in sharpness. When the SID is reduced, the x-ray beam diverges more by the time it reaches the image receptor. This divergence causes increased penumbra, which is the blurred edges of a structure on the image, as the rays are not hitting the receptor in a straight line. The result is that the fine details of the structures being imaged become less distinct and can appear more blurred.

In radiography, maintaining an appropriate SID is crucial for achieving optimal image quality, as increased distances typically enhance the sharpness of the image. Therefore, decreased SID compromises the clarity and resolution needed for precise diagnostic interpretation.