A grid should be usually employed in which of the following circumstances?

A grid should be employed particularly when radiographing a large or dense body part because these conditions typically result in increased scatter radiation. Grids are designed to absorb some of this scatter before it reaches the image receptor. By doing this, grids enhance image quality by improving contrast, making the structures of interest more visible against the background noise of scattered radiation.

Large or dense body parts, such as the abdomen or pelvis, can generate significant scatter due to the volume of tissue being imaged. Without a grid, this scatter can degrade the image quality, resulting in a radiograph that is harder to interpret. Utilizing a grid in these cases significantly improves diagnostic accuracy.

In contrast, while using high kilovoltage can also benefit from a grid due to changes in beam quality and scatter, it is not a direct criterion for grid use like the density and size of the body part is. Also, using a grid does not typically reduce patient dose; in fact, grids often require higher exposure settings to achieve adequate image quality, which can lead to increased dose. Therefore, the most appropriate circumstance for grid utilization is specifically tied to the density or size of the body part being imaged.