Among the exposure factor sets provided, which yields the highest 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 is governed mainly by geometric factors in radiography. The key relationship is that geometric unsharpness grows with object-image distance (OID) and shrinks with a longer source-image distance (SID). If OID is kept constant, increasing SID reduces geometric blur and improves sharpness.

In these options, the OID is the same for all—4 inches—so the difference in resolution comes from SID. The set with the longest SID is 72 inches, which minimizes blur the most and thus provides the highest spatial resolution. The other sets use shorter SIDs (40 or 20 inches), which increases blur and lowers resolution. Exposure parameters like mA (mAs) and kVp affect exposure and image contrast/noise, but not the geometric sharpness described here.