Spatial resolution is directly related to which of the following factors?

Spatial resolution refers to the ability of an imaging system to distinguish fine details in an image. It is influenced by several factors, including the distance from the x-ray tube to the image receptor and the size of the focal spot.

When considering the correct choice, it's important to recognize how the source-to-image distance (SID) impacts spatial resolution. Increasing the SID typically enhances spatial resolution because it reduces the penumbra effect, where the edges of objects appear blurred. A greater distance allows for a more focused beam of radiation to be delivered to the image receptor, resulting in sharper images with finer detail. This is why SID is a key factor directly affecting spatial resolution.

Focal-spot size also plays a crucial role in spatial resolution. A smaller focal spot leads to sharper images as it produces less geometric unsharpness. However, the query specifies a direct relational aspect without indicating a combination of multiple influences; hence the choice that highlights SID alone does not completely encompass the multifaceted nature of spatial resolution influenced by focal-spot size.

While tube current can affect image quality through its impact on radiation exposure and noise, it does not directly influence spatial resolution in the same clear manner as SID does. Thus, considering the relationships at play, the most direct factor impacting