Which statement correctly describes magnification in radiography?

Which statement correctly describes magnification in radiography?

• A. Magnification increases with shorter SID and longer OID
• B. Magnification increases with longer SID and shorter OID
• C. Magnification is unaffected by SID and OID
• D. Magnification only occurs with increased OID

Answer: (A)

Magnification in radiography comes from the geometry of the X-ray beam and how the object sits relative to the source and the receptor. The size of the image on the receptor depends on the magnification factor, which is SID divided by SOD, where SOD is the source-to-object distance (and SOD = SID − OID). When you shorten the SID, the source is closer to the object, and the rays spread more as they reach the receptor, increasing the projected size. When you increase the OID, the object moves farther from the receptor, decreasing SOD and also increasing magnification. So magnification grows with a shorter SID and a longer OID. For intuition, imagine the same object projected onto the detector: bring the X-ray source closer or pull the object farther from the detector; both moves cause the image to appear larger on the film. Keep in mind that increasing magnification often comes at the cost of reduced sharpness due to geometric unsharpness.

Magnification in radiography comes from the geometry of the X-ray beam and how the object sits relative to the source and the receptor. The size of the image on the receptor depends on the magnification factor, which is SID divided by SOD, where SOD is the source-to-object distance (and SOD = SID − OID). When you shorten the SID, the source is closer to the object, and the rays spread more as they reach the receptor, increasing the projected size. When you increase the OID, the object moves farther from the receptor, decreasing SOD and also increasing magnification. So magnification grows with a shorter SID and a longer OID.

For intuition, imagine the same object projected onto the detector: bring the X-ray source closer or pull the object farther from the detector; both moves cause the image to appear larger on the film. Keep in mind that increasing magnification often comes at the cost of reduced sharpness due to geometric unsharpness.