If a radiograph was produced using 12 mAs and 85 kV with a 16:1 ratio grid, what should the new mAs value be when using an 8:1 ratio grid?

To determine the new mAs value when changing from a 16:1 ratio grid to an 8:1 ratio grid, it is essential to understand how grid ratios affect the amount of radiation required to achieve a similar image density.

Grids are designed to improve image quality by reducing scattered radiation that reaches the image receptor. The higher the grid ratio, the more effective the grid is at reducing scatter, but it also requires a higher radiation dose (increased mAs) to maintain the same exposure level. The relationship between grid ratio and the required mAs can be approximated by the factor of the ratios.

In this case, moving from a 16:1 grid to an 8:1 grid means there is a decreased efficiency in scatter reduction. The 16:1 grid has a higher lead content compared to the 8:1 grid, meaning that less mAs is needed to achieve the desired image density when using the 8:1 grid. The general rule of thumb is that using an 8:1 grid will typically require about half the mAs compared to a 16:1 grid.

Starting with 12 mAs at a 16:1 grid, if we apply the factor of efficiency change, we can