Improved Circular Edge Analysis Method for Measuring the Focus Size and Shape in High-Energy Electron Accelerator

To achieve high spatial resolution of X-ray imaging, the focal spot size of high-energy nondestructive testing electron accelerators has been progressively reduced from 2 to below 1 mm, and, in some cases, down to tens of micrometers. To measure these increasingly smaller focal spots, traditional methods such as the “Sandwich” test method and the slit translation scanning method are no longer effective. This article developed an improved circular edge analysis method (ICEAM) for measuring the size and shape of the focal spot of electron accelerators. The ICEAM employs the detector’s point spread function (PSF) to correct the nonideal circular aperture image caused by the X-ray scatter and the detector’s crosstalk. Then, edge spread functions (ESFs) of the corrected circular aperture image are used to construct a sinogram of the focal spot, which is subsequently used to reconstruct the intensity distribution image of the focal spot by using the filtered back-projection (FBP) method. This approach enables precise measurement of both the shape and the size of the focal spot. Theoretical and experimental results demonstrate that ICEAM can not only conveniently and rapidly measure the shape and size of focal spots for conventional high-energy electron accelerators, with measurement errors within 5.8%, but also accurately measure the micrometer-scale focal spots for novel MeV energy electron accelerators (Rhodotron), with measurement errors within 16.2% of the theoretical value. The proposed ICEAM effectively tackles the challenges in measuring the shape and size of the microfocus for novel high-energy electron accelerators, and it is of significant importance for advancing the application of these electron accelerators in digital X-ray imaging and high-end equipment such as industrial CT.