Effect of electrode configurations on the focal spot of x-ray tube

摘要

Ihe grating-based x-ray phase-contrast imaging have more advantages over the conventional x-ray imaging techniques based on the attenuation of x-rays in soft tissues in the medical diagnosis. However, until now the phase contrast imaging technique have not been put into practical uses, one of the reasons is that there is no compact x-ray source suitable for phase signal detection. The x-ray tube that can be used as the source of phase contrast imaging system is becoming the focus of research, the key issues of which could be the shape and the uniformity of focal spot. This paper provided and studied one kind of x-ray tube based on the electron impinging target. According to the system design of the phase contrast imaging, an x-ray tube with square focal spot of 0.8 mm side length was needed. An electrode structure which could form a planar electric field distribution was so designed that the emitted electrons from filament could move to target along straight paths. For comparison, an axis-symmetry field x-ray tube was designed too. The electron trajectories were simulated following the computation of the electric potential distributions in the two cases of electrode structure, respectively. The simulation results show that the x-ray tube of planar field structure may lend more regular square shape to focus spot than the axis-symmetry field structures.