The thicker the tissue, the more the x-ray scatters.
Thick body parts like thorax, abdomen, skull and joints greater than 10 cm require a grid.
A grid is like the focusing lens in a camera.
A high-ratio grid permits FEWER x-rays to pass through it from the animal, but you get a better, more high-resolution radiograph.
The grid prevents scattered radiation from reaching an x-ray film, so that only the primary, directly aimed x-rays penetrate straight into the animal for the best image.
An x-ray grid is basically a plate made of alternating strips of lead, which block scattered x-rays, interspersed between strips of plastic or aluminum, which allow the straight x-rays through. Grids are used in traditional film screen radiography and are frequently used in digital and computed radiography (DR and CR). However, in some DR and CR systems, grids are unnecessary because their effects are digitally reproduced by vendor software.
