Which formula is used to determine the magnification factor?

Which formula is used to determine the magnification factor?

• A. source-to-image distance (SID) - object-to-image distance (OID)
• B. SID / OID
• C. source-to-object distance (SOD) / source-to-image distance (SID)
• D. SID / SOD

Answer: (D)

Magnification reflects how much larger the image is than the actual object, and it depends on where the object and the receptor sit relative to the X-ray source. The standard way to express this is the distance from the X-ray source to the image receptor divided by the distance from the X-ray source to the object. In other words, magnification equals SID / SOD. This makes intuitive sense: if the receptor sits farther away from the source, or the object sits closer to the source (reducing SOD), the ratio grows and the image appears more magnified. An equivalent way to write it is 1 + (OID / SOD), since OID = SID − SOD, which leads to SID / SOD = 1 + OID / SOD. For example, with SID 100 cm and SOD 40 cm, magnification is 2.5. Using SID/OID or SOD/SID does not correctly describe how the image size relates to the object size, so those forms aren’t the right expression for magnification.

Magnification reflects how much larger the image is than the actual object, and it depends on where the object and the receptor sit relative to the X-ray source. The standard way to express this is the distance from the X-ray source to the image receptor divided by the distance from the X-ray source to the object. In other words, magnification equals SID / SOD. This makes intuitive sense: if the receptor sits farther away from the source, or the object sits closer to the source (reducing SOD), the ratio grows and the image appears more magnified. An equivalent way to write it is 1 + (OID / SOD), since OID = SID − SOD, which leads to SID / SOD = 1 + OID / SOD. For example, with SID 100 cm and SOD 40 cm, magnification is 2.5. Using SID/OID or SOD/SID does not correctly describe how the image size relates to the object size, so those forms aren’t the right expression for magnification.