The effect of focal spot size on the spatial resolution of variable resolution X-ray CT scanner

Background: A variable resolution X-ray (VRX) CT scanner provides a great increase in the spatial resolution. In VRX CT scanners, the spatial resolution of the system and its field of view (FOV) can be changed according to the object size. One of the main factors that limit the spatial resolution of VRX CT scanner is the effect of the X-ray focal spot. Materials and Methods: A theoretical study of the effect of X-ray focal spot on the spatial resolution of VRX CT is presented in this paper. In this study, we used the parameters of an actual VRX CT scanner. By using the relevant equations, the effects of foal spot sizes of 0.6 and 0.1 mm were calculated on spatial resolution of the system at various opening half angles. Results: Focal spot size of 0.6 mm had no significant effect on spatial resolution of the system for opening half angles of above 14°. Even focal spot sizes of larger than 0.6 mm could not affect the spatial resolution of the system. For opening half angles of below 14°, foal spot size of 0.6 mm limited the spatial resolution of the system to 5.7 cycle/mm and caused great spatial resolution non-uniformity along the detector length. Conclusion: By focal spot size of 0.1 mm, the spatial resolution varied as a function of the opening half angle and increased to more than 30 cycle/mm. Additionally, focal spot size of 0.1 mm minimized the spatial resolution non-uniformity along the detector length.