Grid cutoff occurs when:

Grid cutoff is a phenomenon that occurs when there is improper alignment between the x-ray tube and the grid. Grids are used in radiography to improve image quality by absorbing scattered radiation while allowing primary radiation to pass through. However, if the x-ray tube is not correctly positioned in relation to the grid, some primary radiation may be blocked by the grid itself, leading to a reduction in image density in certain areas of the radiograph. This misalignment can result from the tube being angled incorrectly or the grid being off-centered, ultimately resulting in a portion of the image appearing darker or lighter than intended.

The other scenarios mentioned do not directly relate to grid cutoff. For instance, if the x-ray tube is too far from the grid, it may affect the overall image quality, but it does not specifically cause grid cutoff. Similarly, the grid cannot absorb all primary radiation under normal operation, as that would defeat its purpose. Patient movement during the exposure can cause motion artifacts but does not relate to the alignment of the grid and x-ray tube, which is at the core of grid cutoff.