At what body-part thickness is the use of a grid recommended?

• A. 5 cm
• B. 8 cm
• C. 15 cm
• D. 20 cm

Answer: (B)

When imaging, scattered photons inside the body degrade image contrast. A grid sits between the patient and the film to absorb much of this scatter while letting the primary beam reach the detector, which improves image quality. The point at which scatter starts to noticeably affect contrast—and thus a grid becomes beneficial—occurs as the part gets thicker. In many radiography guidelines, that tipping point is around eight centimeters of thickness. Below that, scatter is usually manageable without a grid, so using one offers less benefit and would raise the patient dose and technique requirements. Above this thickness, a grid is routinely used to preserve contrast. So eight centimeters is the practical threshold where grid use becomes recommended, with thicker parts like fifteen or twenty centimeters clearly warranting it.