CAMRT Radiography Practice Exam

Does a high grid ratio focusing range have a smaller or larger range?

1. Larger focusing range

2. Smaller focusing range

3. No effect on the focusing range

4. Depends on the type of grid used

The correct answer is: Smaller focusing range

A high grid ratio is associated with a smaller focusing range. The focusing range of a grid refers to the distance within which the primary x-rays should be directed in order for the grid to effectively absorb scatter radiation while allowing the primary beam to pass through. When a grid has a high ratio, it means that the grid strips are relatively tall compared to their interspace material. This design leads to a stricter requirement on the angle of the x-ray beam entering the grid. Consequently, this results in a more limited range of acceptable distances and angles from which the central ray can approach the grid. As a result, the high grid ratio effectively necessitates a smaller focusing range to ensure optimal image quality. Additionally, grids are often categorized by their ratio – for example, a grid with a 16:1 ratio will have a tighter focusing range than a grid with a 5:1 ratio. Thus, the nature of a high grid ratio indeed contributes to a smaller focusing range, making the provided answer correct.