The determination of the focal spot size of an X-ray tube from the radiation beam profile

• A model of the X-ray beam profile allows the determination of the focal spot size.
• A general profile function fits the data measurements of the beam profile.
• Links between beam profile and line spread and edge spread functions are discussed.
• No need for additional or specific devices to estimate the focal spot size.

The aim of this work is to show that the focal spot size of a given X-ray tube can be determined from the profile of the radiation beam without the use of devices specifically designed for that task. The approach presented relies on a simple model for the radiation beam profile and on an analytical function used to fit the beam profile data. The basics of the profile function are outlined and the relationship between the fitting and the profile parameters are deduced. The relationship of the proposed method with the edge spread function and line spread function concepts is discussed. The focal spot size of an X-ray tube used at the Laboratory for Metrology of Ionizing Radiation (LMRI) of IST was determined using the proposed method. In the analysis of the experimental results, the heel-effect was also evaluated.