What is the relationship between object-to-image distance (OID) and entrance skin exposure (ESE)?

The relationship between object-to-image distance (OID) and entrance skin exposure (ESE) is that they are directly related. This means that as OID increases, the entrance skin exposure also increases. The reason for this relationship is rooted in the geometry of radiation and the way it interacts with the imaging system.

When the OID is greater, the radiation beam must travel a longer distance to reach the image receptor after passing through the object. This increase in distance generally leads to an increase in the radiographic dose to the skin because more scatter and primary radiation can be absorbed by the tissues before reaching the image receptor. Essentially, a larger OID can reduce the amount of radiation reaching the image receptor directly but can result in more scatter radiation, increasing the dose to the skin in the process.

In scenarios where OID is kept minimal, the radiation has a more direct path to the image receptor, potentially lowering the dose at the entrance skin. Conversely, as OID increases, the chances of increased skin dose from both primary and scattered radiation also grow, establishing a direct relationship in the context of entrance skin exposure.