What term describes the phenomenon where the image intensity is greater at the center than at the edges?

The phenomenon where the image intensity is greater at the center than at the edges is referred to as vignetting. This visual effect is commonly observed in imaging systems, including those used in fluoroscopy and radiology. Vignetting occurs due to several factors, including lens design, the position of the light source, and the sensitivity of the imaging detector.

In practical terms, vignetting creates a gradual fade of brightness from the center towards the corners of an image, which can impact the overall quality and diagnostic potential of the images produced. Understanding vignetting is crucial for radiologists and imaging professionals to ensure they interpret images correctly and account for any potential distortions resulting from this effect.

Other terms like lag, quantum mottle, and pincushion effect describe different phenomena related to imaging but do not apply to the description of intensity variation from center to edges. Lag relates to the time delay in sensor response, quantum mottle refers to noise created by insufficient photon statistics, and the pincushion effect is a type of distortion where images appear pinched in the center. Thus, vignetting is distinctly characterized by its gradient of intensity, accurately representing the question's criteria.