What are the tradeoffs between spot size, magnification and resolution?
The combination of focal spot size and magnification determines the theoretical maximum resolution in the x-ray image. The finite spot size of the x-ray source creates a penumbra around the edges of the x-ray shadow, much like the sun casting a shadow of your hand. A larger spot size and a longer object-to-detector distance (ODD) both increase the penumbra and thus the minimum feature size detectable at the image plane. The geometric magnification factor is given by the ratio of the source-to-detector distance (SDD) to the source-to-object distance (SOD). The minimum feature size is calculated by multiplying the focal spot size by the ratio of the ODD to SOD. The camera resolution (pixel size and scintillator) needs to be matched to these parameters in order to be able to image the required features.
