Which device is primarily used to reduce scatter radiation reaching the film?

• A. Grid
• B. Cassette
• C. Collimator
• D. Filter

Answer: (A)

Scatter radiation fogs the image and lowers contrast by adding unwanted exposure to the film. The device designed to minimize this effect is the anti-scatter grid. It sits between the patient and the film and is made of alternating lead strips and radiolucent interspace material. Scattered photons, which travel in many directions, are more likely to be absorbed by the lead strips, while primary photons travel more directly toward the film and pass through the interspaces. This selective absorption reduces fog and improves image contrast. Keep in mind that using a grid requires increasing exposure to compensate for the loss of some primary photons. The cassette simply houses the film, the collimator narrows the X-ray beam to limit field size and dose, and a filter hardens the beam by removing low-energy photons—neither is primarily tasked with reducing scatter reaching the film.