What is the role of a grid in radiography?

• A. It reduces patient dose by absorbing photons
• B. It decreases image contrast
• C. It absorbs primary beam to prevent overexposure
• D. It improves image contrast by absorbing scattered radiation; requires higher exposure to compensate

Answer: (D)

The main idea here is how a grid controls scattered radiation to improve image quality. When x-rays pass through the patient, some photons scatter in all directions. This scattered radiation adds a uniform fog to the image and lowers contrast, making it harder to see details. A grid, made of alternating lead strips and radiolucent spacers, sits between the patient and the image receptor and absorbs many of these scattered photons before they reach the detector. That reduction in scatter leads to higher image contrast and better visibility of anatomy.

Because the grid also absorbs some of the primary beam, you must increase the exposure to keep the receptor image adequately exposed. This is why using a grid typically requires a higher technique (more mA or longer exposure) than without a grid—the grid factor accounts for the loss of primary photons. It’s not about reducing patient dose; the grid often results in a higher dose to compensate for the primary photon absorption. The grid’s purpose is not to decrease contrast or to absorb only the primary beam to prevent overexposure; its role is to clean up scatter and improve contrast by absorbing scattered photons.