Anti-Scatter Grids in Radiography: Grid Ratios, Focal Distance, and Dose
When to use a grid, when to remove it, and how to avoid grid cutoff artifacts.
Table of Contents
1. The Problem of Compton Scatter Radiation
When X-ray beams encounter tissue thicker than 10–12 cm, many photons undergo Compton scattering, deflecting randomly and striking the detector at oblique angles. This creates a uniform fog of useless exposure, degrading contrast. Anti-scatter grids use alternating thin lead strips separated by radiolucent aluminum or carbon interspacers to absorb angled scattered photons while allowing primary straight-line photons to pass through.
3. When to Remove Grids: ALARA Radiation Protection
Because lead strips also absorb a portion of useful primary beam photons, using a grid requires increasing patient exposure (mAs) by a factor of 3x to 5x (the Bucky factor). Grids should always be removed when imaging pediatric patients or extremities under 10 cm thick to prevent unnecessary radiation exposure.