Which change to exposure geometry would most effectively reduce receptor exposure for a portable chest exam when dose must be kept low?

Which change to exposure geometry would most effectively reduce receptor exposure for a portable chest exam when dose must be kept low?

• A. Decrease SID
• B. Increase filtration
• C. Increase SID
• D. Increase grid ratio

Answer: (C)

Increasing the distance between the X-ray source and the patient (exposure geometry) lowers receptor exposure because of the inverse square law: as you move the source farther away, the beam spreads out and the intensity at the receptor drops quickly (roughly a quarter of the exposure if you double the distance). For a portable chest exam where keeping dose low is important, this distance increase is the most effective way to reduce the radiation reaching the image receptor without changing technique, compared with other geometry-based options. Decreasing the distance would raise receptor exposure, so that wouldn’t help. Filtration lowers patient dose by removing low-energy photons but isn’t a geometry change and doesn’t directly reduce receptor exposure the same way distance does. Increasing grid ratio does reduce scattered radiation and can lower receptor exposure, but it also absorbs more primary photons and typically requires higher technique to maintain image brightness, making it less straightforward for reducing exposure in this context.

Increasing the distance between the X-ray source and the patient (exposure geometry) lowers receptor exposure because of the inverse square law: as you move the source farther away, the beam spreads out and the intensity at the receptor drops quickly (roughly a quarter of the exposure if you double the distance). For a portable chest exam where keeping dose low is important, this distance increase is the most effective way to reduce the radiation reaching the image receptor without changing technique, compared with other geometry-based options.

Decreasing the distance would raise receptor exposure, so that wouldn’t help. Filtration lowers patient dose by removing low-energy photons but isn’t a geometry change and doesn’t directly reduce receptor exposure the same way distance does. Increasing grid ratio does reduce scattered radiation and can lower receptor exposure, but it also absorbs more primary photons and typically requires higher technique to maintain image brightness, making it less straightforward for reducing exposure in this context.