What happens to spatial resolution if the focal spot size is increased?

When the focal spot size is increased, spatial resolution decreases. This relationship stems from the fact that a larger focal spot produces a wider area of X-ray production, which in turn leads to a greater blur in the image. Spatial resolution refers to the ability to distinguish between small structures in an image, and a smaller focal spot allows for more precise and detailed imaging.

A smaller focal spot size contributes to higher spatial resolution by reducing the amount of penumbra, which is the transition zone between the fully exposed area and the unexposed area. With a larger focal spot, the penumbra effect becomes more pronounced, as the X-rays spread over a larger area, thus creating more blur and reducing the ability to resolve fine details.

In summary, increasing the focal spot size leads to a decrease in spatial resolution, as it compromises the sharpness and detail needed to interpret the images accurately.