How does an increase in OID (Object-to-Image Distance) affect spatial resolution?

An increase in Object-to-Image Distance (OID) decreases spatial resolution primarily due to the increased divergence of the x-ray beam as it travels from the object to the imaging receptor. As the OID increases, the x-ray beam spreads out more, leading to greater penumbra or halo effects around the edges of the structures being imaged. This results in less sharpness and clarity of the image, reducing the ability to distinguish fine details between adjacent structures.

Furthermore, the longer the distance the x-rays must travel, the more scatter can occur, which further contributes to a loss of image quality. This scatter adds unwanted density to the image, which can blur fine details, worsening the spatial resolution. Thus, increasing OID negatively impacts the clarity of the image, making it more challenging to accurately identify small anatomical features or pathologies.

In contrast, decreasing OID would have a beneficial effect on spatial resolution, as the beam would be less divergent and produce a sharper image with clearer detail.