American Registry of Radiologic Technologists (ARRT) Practice Exam

Increasing the SID will have what effect on recorded detail?

1. Decrease it

2. Increase it

3. No change

4. Only affect patient exposure

The correct answer is: Increase it

Increasing the Source-to-Image Distance (SID) enhances recorded detail due to the reduction of penumbra, which results from the increased distance between the x-ray tube and the image receptor. Penumbra is the blurred area around the edges of a radiographic image; by maximizing the distance, the x-ray beam converges more precisely at the receptor, leading to sharper images. This principle of geometry in radiography indicates that a larger SID minimizes the divergence of the x-ray beam, improving the resolution of the details on the film or digital detector. While increasing the SID does not directly affect patient exposure levels, it is significant to consider how it may influence those levels indirectly by requiring a longer exposure time to maintain adequate density, depending on the imaging technique used. Nevertheless, the main effect of increasing SID is the improvement in the sharpness and detail of the resultant image.