When the source-to-image distance (SID) is 80 cm (31.5 inches), the actual SID should match the displayed SID within a range of

When the source-to-image distance (SID) is 80 cm (31.5 inches), the actual SID should match the displayed SID within a range of

• A. +/- 0.8 cm (0.3 inch)
• B. +/- 4.0 cm (1.5 inches)
• C. +/- 1.6 cm (0.6 inch)
• D. +/- 8.0 cm (3.1 inches)

Answer: (C)

SID accuracy is governed by a tolerance expressed as a percentage of the indicated distance. In QA practice, the actual SID should fall within ±2% of the displayed SID. For an 80 cm SID, that translates to a range of 78.4 cm to 81.6 cm, i.e., a tolerance of ±1.6 cm. The other options represent different percentages (1%, 5%, 10%), which are not the standard tolerance. Maintaining this ±2% range helps ensure correct image magnification and geometric accuracy in radiographs.

SID accuracy is governed by a tolerance expressed as a percentage of the indicated distance. In QA practice, the actual SID should fall within ±2% of the displayed SID. For an 80 cm SID, that translates to a range of 78.4 cm to 81.6 cm, i.e., a tolerance of ±1.6 cm. The other options represent different percentages (1%, 5%, 10%), which are not the standard tolerance. Maintaining this ±2% range helps ensure correct image magnification and geometric accuracy in radiographs.