On a portable chest radiograph of a very small patient, the receptor exposure is higher than desired even with low mAs and kVp. How can the technologist decrease receptor exposure?

On a portable chest radiograph of a very small patient, the receptor exposure is higher than desired even with low mAs and kVp. How can the technologist decrease receptor exposure?

• A. Decrease the diagnostic filtration
• B. Decrease the anode angle
• C. Increase the source-to-image distance (SID)
• D. Decrease the grid ratio

Answer: (C)

The key idea is how distance affects beam intensity at the image receptor. The x-ray beam does not deliver the same amount of energy to the receptor as you move farther away from the patient; it follows the inverse square law, meaning the intensity drops with the square of the distance. Increasing the source-to-image distance reduces the photons reaching the receptor, so receptor exposure decreases even when mAs and kVp stay low. This is particularly useful on portable exams of very small patients, where you want to bring exposure down without changing technique factors that would affect image quality or patient dose in other ways. Why the other options aren’t helpful here: decreasing filtration would actually let more low-energy photons reach the receptor, increasing exposure rather than decreasing it; altering the anode angle changes the beam’s distribution and field in a way that isn’t a reliable or standard method for reducing receptor exposure in this scenario; decreasing the grid ratio would allow more primary photons to pass through the grid, increasing receptor exposure rather than reducing it.

The key idea is how distance affects beam intensity at the image receptor. The x-ray beam does not deliver the same amount of energy to the receptor as you move farther away from the patient; it follows the inverse square law, meaning the intensity drops with the square of the distance. Increasing the source-to-image distance reduces the photons reaching the receptor, so receptor exposure decreases even when mAs and kVp stay low. This is particularly useful on portable exams of very small patients, where you want to bring exposure down without changing technique factors that would affect image quality or patient dose in other ways.

Why the other options aren’t helpful here: decreasing filtration would actually let more low-energy photons reach the receptor, increasing exposure rather than decreasing it; altering the anode angle changes the beam’s distribution and field in a way that isn’t a reliable or standard method for reducing receptor exposure in this scenario; decreasing the grid ratio would allow more primary photons to pass through the grid, increasing receptor exposure rather than reducing it.