Which factor determines image magnification?

• A. Resolution of the receptor
• B. Beam quality
• C. Object contrast
• D. Ratio of SOD to OID

Answer: (D)

Magnification is determined by the geometry of the imaging setup—the distances between the X-ray tube (source), the object, and the image receptor. The larger the object-to-receptor distance (OID) or the smaller the source-to-object distance (SOD), the bigger the image will appear. This relationship is captured by the idea that image size grows with the overall source-to-image distance (SID) and shrinks as the object moves farther from the source relative to its distance to the receptor. In terms of the two distances, considering how SOD compares to OID gives a practical handle on magnification: as the ratio SOD to OID increases, magnification decreases; as that ratio decreases, magnification increases. Because of this geometric interplay, the ratio of SOD to OID directly influences how large the image looks.

Other factors like receptor resolution, beam quality, and object contrast affect image sharpness, noise, and visibility, but they do not change the actual size of the projected image.