Which set would produce the best spatial resolution?

• A. 60 mAs, 80 kVp, 72-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: (A)

Spatial resolution improves when geometric unsharpness is minimized. Geometric unsharpness is proportional to the focal spot size times the object-to-image distance (OID) divided by the image receptor distance (SID). Since OID is the same across all options, the key difference is SID. The longest SID (72 inches) produces the least geometric blur, yielding the sharpest edges, even though exposure factors mainly affect brightness and noise rather than resolution. Higher mAs can reduce quantum mottle and improve perceived image quality, but it doesn’t reduce blur caused by the geometry. Therefore, the combination with the 72-inch SID will give the best spatial resolution.