What is the function of a grid?

• A. Absorb primary radiation
• B. Absorb remnant radiation
• C. Absorb scattered radiation
• D. Absorb low energy radiation before it reaches the image receptor

Answer: (C)

Grids are used to boost image contrast by cutting down scatter. When X-rays pass through the patient, some photons scatter in many directions. Those scattered photons travel to the image receptor and create a fog that hides fine details. A grid placed between the patient and the receptor has lead strips with spaces between them; the lead strips absorb much of the scatter, especially photons coming at oblique angles, while the primary photons that travel in the intended direction mostly pass through the gaps to the receptor. By reducing the scatter reaching the film or detector, the image shows greater contrast and clearer detail. It’s worth noting that a grid does not primarily absorb primary radiation—that would darken the image and require higher exposure—and its main job isn’t to filter out low-energy photons before they reach the receptor, although some absorption of such photons occurs incidentally. The essential idea is absorbing scattered radiation to improve image quality.