Spatial resolution is inversely related to which factor?

Spatial resolution refers to the ability of an imaging system to distinguish between objects that are close together. It is influenced by several factors, one of the most significant being object-to-image distance, or OID. When OID increases, the sharpness of the image typically decreases, leading to poorer spatial resolution. The relationship is inversely proportional; as OID increases, spatial resolution decreases.

A larger OID means that the distance between the object being imaged and the imaging receptor is greater. This greater distance allows for more scattering of the x-ray photons before they reach the receptor, which can result in a loss of detail in the image, thus negatively affecting spatial resolution.

The other factors mentioned, such as source-to-image distance (SID) and grid ratio, while they do have an impact on image quality, do not have the same direct and inverse relationship with spatial resolution as OID does. Increasing SID could actually improve spatial resolution by reducing the amount of divergence in the x-ray beam, and grid ratio relates more to image contrast than resolution.

Therefore, focusing on the relationship between OID and spatial resolution clarifies why OID is the correct choice in the context of this question.