Which of the following is an exposure parameter rather than a beam geometry parameter?

Which of the following is an exposure parameter rather than a beam geometry parameter?

• A. Source-to-image distance (SID)
• B. Milliampere-seconds (mAs)
• C. Object-to-image distance (OID)
• D. Tube angulation

Answer: (B)

Distinguishing exposure factors from geometric factors is what this question tests. Milliampere-seconds (mAs) is the exposure parameter: it directly controls the number of X-ray photons produced and reaching the image receptor, determining receptor exposure and image density. It relates to how bright the image will look and the dose to the patient, independent of how the beam is geometrically arranged. The other options are geometric factors. Source-to-image distance changes beam intensity at the receptor via the inverse-square law and alters magnification. Object-to-image distance affects magnification and sharpness, while tube angulation changes the projection geometry and can cause distortion.

Distinguishing exposure factors from geometric factors is what this question tests. Milliampere-seconds (mAs) is the exposure parameter: it directly controls the number of X-ray photons produced and reaching the image receptor, determining receptor exposure and image density. It relates to how bright the image will look and the dose to the patient, independent of how the beam is geometrically arranged.

The other options are geometric factors. Source-to-image distance changes beam intensity at the receptor via the inverse-square law and alters magnification. Object-to-image distance affects magnification and sharpness, while tube angulation changes the projection geometry and can cause distortion.