Final answer:
Increasing the source-to-image distance (SID) causes a decrease in the patient dose due to the inverse square law of radiation. The increased distance leads to a lower radiation intensity at the patient's location, and thus the dose is reduced.
Step-by-step explanation:
When discussing the effect of increasing the source-to-image distance (SID) on patient dose in the context of radiographic imaging, the key principle involved is the inverse square law of radiation. The inverse square law states that the intensity of radiation is inversely proportional to the square of the distance from the source. Thus, if you increase the SID, the radiation intensity at the image receptor (or patient) decreases, which in turn means the patient dose will decrease as well. For example, if the SID is doubled, the radiation intensity at the image receptor would be reduced to one-fourth of its original value. This is because the area over which the radiation is spread increases with the square of the distance, diminishing the intensity of radiation per unit area. Hence, increasing the SID is a strategy used to reduce the patient dose without compromising the image quality significantly, provided other factors such as exposure time and kVp (kilovolt peak) are adequately adjusted.