What is the purpose of an anti-scatter grid and how does grid ratio influence image quality and patient dose?

• A. Grid absorbs scattered photons to improve contrast; higher grid ratio improves contrast but requires higher exposure (dose).
• B. Grid increases scattered photons.
• C. Grid ratio has no effect on dose.
• D. Higher grid ratio reduces patient dose.

Answer: (A)

Anti-scatter grids work by absorbing scattered photons that originate from the patient before they reach the image receptor, which reduces fog and increases image contrast. The grid ratio—the height of the lead strips relative to the interspace distance—determines how much attenuation the grid provides. A higher grid ratio means more lead and stronger attenuation, so scatter is reduced even further and image contrast improves. But that same increased attenuation also cuts into the primary beam, so to keep the same receptor exposure you must increase the exposure (more mA or longer exposure time), which raises the patient dose. So the trade-off is clear: higher grid ratio boosts contrast but at the cost of higher dose and potentially more challenging alignment.

The other statements don’t fit: a grid does not increase scattered photons; grid ratio does influence dose (increasing it when compensating for attenuation); and higher grid ratio does not reduce patient dose.