What is the distance between the anatomy being imaged and the focal spot called?

What is the distance between the anatomy being imaged and the focal spot called?

• A. source-to-image distance (SID)
• B. object-to-image distance (OID)
• C. source-to-object distance (SOD)
• D. focal spot size (FSS)

Answer: (C)

The distance between the X-ray focal spot and the anatomy being imaged is called the source-to-object distance. This term specifically describes how far the object (the anatomy) sits from the X-ray source, which, together with the object-to-image distance, influences image magnification and sharpness. Magnification is roughly SID divided by SOD, so changing how close the object sits to the focal spot will change how large the image appears. The other terms refer to different gaps: source-to-image distance is from the focal spot to the image receptor, and object-to-image distance is from the object to the receptor. Focal spot size is the physical size of the X-ray source itself.

The distance between the X-ray focal spot and the anatomy being imaged is called the source-to-object distance. This term specifically describes how far the object (the anatomy) sits from the X-ray source, which, together with the object-to-image distance, influences image magnification and sharpness. Magnification is roughly SID divided by SOD, so changing how close the object sits to the focal spot will change how large the image appears. The other terms refer to different gaps: source-to-image distance is from the focal spot to the image receptor, and object-to-image distance is from the object to the receptor. Focal spot size is the physical size of the X-ray source itself.