CAMRT Radiography Practice Exam

In radiography, what effect does a longer SID have on magnification?

1. It reduces magnification

2. It increases magnification

3. It has no effect on magnification

4. It only affects film size

The correct answer is: It reduces magnification

A longer source-to-image distance (SID) has a significant impact on the level of magnification observed in radiographic images. When SID is increased, the radiation emitted from the X-ray tube travels a greater distance before it reaches the imaging receptor. This increased distance causes the rays to diverge less as they approach the object being imaged, resulting in a more accurate representation of the object's size. Consequently, the reduction of magnification occurs because the rays that create the image are more parallel. This minimization of the divergence leads to a clearer and more proportionate depiction of the object, allowing for more precise measurements and assessments. In clinical practice, achieving a longer SID is often desirable for enhancing image quality by reducing distortion and magnification of the structures being examined. In contrast, a shorter SID would lead to increased magnification, as the X-ray beam would diverge more, causing the objects to appear larger on the image than they actually are. Thus, the correct answer reflects the fundamental principle of radiographic imaging that increasing the distance from the X-ray source to the image receptor helps to produce images with reduced magnification.