In an extreme case of off-focus grid error, which of the following may occur?

In an extreme case of off-focus grid error, the phenomenon of increased brightness and quantum mottle at the edges of the image can occur due to the misalignment of the grid with the x-ray beam. An off-focus or misaligned grid allows more radiation to reach the detector at the periphery of the exposure area, which results in an overexposed appearance along the edges. This can contribute to brightness levels that are higher than expected in those outer regions.

Additionally, the presence of quantum mottle, which refers to the graininess or noise in the radiographic image due to insufficient exposure to x-rays, can be exacerbated in these areas. When there is an increase in brightness, it often indicates a higher dose of radiation reaching those edges, but at the same time, the inconsistent distribution of incoming photons can lead to a noticeable grainy texture, illustrating the negative impact of the grid error.

In contrast, if the grid is functioning properly or not significantly misaligned, the exposure would be more uniform across the image, minimizing both brightness variations and quantum mottle. Therefore, the specific conditions of an extreme off-focus grid error lead to this unique combination of increased brightness and noise at the image edges.