Introduction to Anti-Scatter Grids

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X-ray grids improve the sharpness of x-ray images by trapping the greater part of scatter radiation, resulting in a cleaner, clearer and more detailed image.

One of the most important factors in choosing a grid is grid ratio. The ratio of a grid is the relation between the height of the lead strips to the distance between them. The higher the ratio, the more radiation trapped, and the more effective the grid.

A variety of x-ray grids are available, and each varies in quality, size, configuration and recommended application. Understanding basic grid terminology will help you choose the right grid for your application.

FOCUSED GRID

PARALLEL GRID

CRISS-CROSS GRID

In a focused grid, the lead strips are tilted progressively as they move away from the center. Lines through each of these strips would converge at a point known as the grid focus.

With a parallel grid, only lead strips directly under the x-ray tube are perfectly aligned with the primary rays. To minimize shadows cast by strips not in alignment, use grid ratios no higher than 6:1 and tube-grid distances no less than 48".

A criss-cross grid is actually two grids enclosed in a cover, one above the other, their grid lines perpendicular. Available either focused or parallel, they are generally more than twice as effective as linear grids of equal ratio.

SELECTION BASED ON CLEAN-UP REQUIREMENTS

CLEAN-UP

RATIO/ TYPE

POSITIONING LATITUDE

RECOMMENDED

UP TO

REMARKS

Superlative

15:1

Critical

120 - 140 KVP

Not recommended for tilted tube techniques

Excellent

12:1 Linear

Very slight

110 KVP

(Suitable for higher KV)

Extra care required for proper alignment; usually used in fixed mount.

6:1

Good

100 KVP

Tube tilt limited to five degrees.

Good

8:1 / 10:1 Linear

Distance fair; centering and

leveling - slight

100 KVP

For general stationary grid use.

Moderate

6:1 Linear

Good

80 KVP

Greatest Positional Latitude of stationary grids.

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