For an SID of 80 cm, the acceptable actual SID range is:

For an SID of 80 cm, the acceptable actual SID range is:

• A. 80.0 to 82.0 cm
• B. 79.0 to 81.0 cm
• C. 78.4 to 81.6 cm
• D. 77.0 to 83.0 cm

Answer: (C)

Maintaining a fixed source-to-image distance (SID) within a small tolerance is crucial because even small changes in SID alter image magnification and sharpness. The standard often used for SID tolerance is ±2% of the requested SID. For an SID of 80 cm, 2% equals 1.6 cm. Subtracting and adding that from 80 gives 80 − 1.6 = 78.4 cm and 80 + 1.6 = 81.6 cm. So the acceptable actual SID range is 78.4 to 81.6 cm. This symmetric range ensures the radiograph’s geometry stays consistent, avoiding too much magnification or too little. The other options either don’t cover the full allowable spread or exceed it, so they don’t represent the standard tolerance for an 80 cm SID.

Maintaining a fixed source-to-image distance (SID) within a small tolerance is crucial because even small changes in SID alter image magnification and sharpness. The standard often used for SID tolerance is ±2% of the requested SID. For an SID of 80 cm, 2% equals 1.6 cm. Subtracting and adding that from 80 gives 80 − 1.6 = 78.4 cm and 80 + 1.6 = 81.6 cm. So the acceptable actual SID range is 78.4 to 81.6 cm. This symmetric range ensures the radiograph’s geometry stays consistent, avoiding too much magnification or too little. The other options either don’t cover the full allowable spread or exceed it, so they don’t represent the standard tolerance for an 80 cm SID.