The central ray indicator must align to the actual center of the x-ray field within what tolerance?

• A. 2% SID
• B. 5% SID
• C. 10% SID
• D. 1% SID

Answer: (D)

Precise beam alignment is essential in radiography because the central ray defines where exposure is directed and how the image will be formed. The central ray indicator must line up with the actual center of the x‑ray field within a very tight tolerance to ensure the radiation field and the light field are congruent, so the intended anatomy is centered and not clipped at the edges. Keeping this within one percent of the source-to-image distance minimizes geometric errors that could shift exposure off-center or distort magnification. If the tolerance were looser, even small misalignments could show up on the image, affecting accuracy and consistency, especially at longer distances. Therefore, the required standard is within one percent of SID.