Which set of exposure factors would produce the poorest spatial resolution?

Which set of exposure factors would produce the poorest spatial resolution?

• A. 60 mAs, 80 kVp, 40-inch SID, 4-inch OID
• B. 30 mAs, 92 kVp, 40-inch SID, 4-inch OID
• C. 120 mAs, 92 kVp, 20-inch SID, 4-inch OID
• D. 15 mAs, 100 kVp, 40-inch SID, 4-inch OID

Answer: (C)

Spatial resolution is mainly affected by geometric factors, especially the distance from the focal spot to the image receptor (SID) and the object-to-image distance (OID). When OID is held constant, a shorter SID increases magnification and geometric unsharpness, making edges blurrier and reducing sharpness. In these options, OID is the same for all (4 inches), while SID varies. The shortest SID is 20 inches, which produces the most magnification and blur, leading to the poorest spatial resolution. The other sets use 40-inch SID, which minimizes magnification and improves sharpness. Therefore, the factors that produce the poorest spatial resolution are the exposure factors with the smallest SID.

Spatial resolution is mainly affected by geometric factors, especially the distance from the focal spot to the image receptor (SID) and the object-to-image distance (OID). When OID is held constant, a shorter SID increases magnification and geometric unsharpness, making edges blurrier and reducing sharpness. In these options, OID is the same for all (4 inches), while SID varies. The shortest SID is 20 inches, which produces the most magnification and blur, leading to the poorest spatial resolution. The other sets use 40-inch SID, which minimizes magnification and improves sharpness. Therefore, the factors that produce the poorest spatial resolution are the exposure factors with the smallest SID.