To reduce magnification, which distance parameter should be decreased?

To reduce magnification, which distance parameter should be decreased?

• A. OID
• B. SID
• C. FSS
• D. kVp

Answer: (A)

Magnification in radiography comes from the geometry of the beam as it travels from the focal spot to the receptor. The apparent size of the anatomy on the image grows as the distance between the object and the image receptor (OID) increases, because the divergent X-ray beams project a larger image when the object sits farther from the detector. Decreasing OID places the object closer to the receptor, which reduces the projection enlargement and yields an image that more closely matches the true size of the object. The other factors listed affect exposure, contrast, or sharpness rather than the image size: changing the source-to-image distance would alter magnification in the opposite direction, while focal spot size and kVp influence sharpness and exposure but not the magnification in the same way.

Magnification in radiography comes from the geometry of the beam as it travels from the focal spot to the receptor. The apparent size of the anatomy on the image grows as the distance between the object and the image receptor (OID) increases, because the divergent X-ray beams project a larger image when the object sits farther from the detector. Decreasing OID places the object closer to the receptor, which reduces the projection enlargement and yields an image that more closely matches the true size of the object. The other factors listed affect exposure, contrast, or sharpness rather than the image size: changing the source-to-image distance would alter magnification in the opposite direction, while focal spot size and kVp influence sharpness and exposure but not the magnification in the same way.