How does increasing the source-to-image distance (SID) affect size distortion in radiography?

How does increasing the source-to-image distance (SID) affect size distortion in radiography?

• A. Size distortion increases
• B. Size distortion remains the same
• C. Size distortion decreases
• D. Size distortion becomes unpredictable

Answer: (C)

When the distance from the source to the image plane is increased, the projection of the object onto the detector is less exaggerated. The x-ray beams diverge less across the space between the object and the detector, so the image on the detector is closer in size to the actual object. In other words, magnification drops as SID increases, which reduces size distortion. This change also helps with sharpness, since the geometric blur from the finite focal spot becomes less pronounced over the longer distance.

When the distance from the source to the image plane is increased, the projection of the object onto the detector is less exaggerated. The x-ray beams diverge less across the space between the object and the detector, so the image on the detector is closer in size to the actual object. In other words, magnification drops as SID increases, which reduces size distortion. This change also helps with sharpness, since the geometric blur from the finite focal spot becomes less pronounced over the longer distance.