Imaging of Focal Spots by Means of the Star Test Pattern

Abstract

Magnified radiographic images of the star test pattern yield information on the energy distribution in the focal spot allowing determination of the effective focal spot size, which may not be the same as that imaged by pinhole cameras. Variations in focal spot size induced by varying source intensity, magnification, and direction can also be determined. The star test pattern has demonstrated that by increasing milliamperage the effective focal spot doubles, although this phenomenon was expected, it was quickly determined with the test pattern. An appendix is included to describe the mathematical considerations.