Which description best fits a focused grid?

A focused grid is designed to improve image quality by compensating for the angle of the x-ray beam as it diverges from the tube. In this type of grid, the lead strips are not perfectly vertical; rather, they are angled to coincide with the path of the x-ray photons as they travel towards the image receptor. This angling allows the grid to more effectively absorb scattered radiation while allowing unscattered radiation to pass through, thereby reducing image fog and enhancing contrast.

The description of strips angled to match the divergent beam accurately captures the essence of how focused grids function. This alignment is critical for achieving the desired benefits of using a grid, particularly in situations where a focused approach is needed to manage scatter effectively.

Other descriptions, while they have their own significance in radiography, do not accurately characterize focused grids. For instance, having strips aligned parallel to the x-ray beam refers to parallel grids, which do not account for beam divergence and therefore may not perform as well in certain clinical scenarios. Grids with an infinite source-to-image distance are a concept relevant to other types of grids and not exclusive to focused grids, while the notion of grids used exclusively for portable devices applies to a narrower category of mobile imaging equipment but does not define the focused grid