New Measurement Methods of Focal Spot Size and Shape of X-ray Tubes in Digital Radiological Applications in Comparison to Current Standards

Unsharpness in the image may reduce the visibility of details. Magnification is often required to achieve a spatial resolution similar to film technique, when using digital systems. A part of the unsharpness results from the focal spot size. To determine the effective focal spot size, thousands of images with different tubes, energies, magnifications and IQIs from different EN and ASTM standards were taken to evaluate the influence of the unsharpness in the digital image due to the focal spot. This leads to reference values for the effective focal spot size of the different tubes. These reference values were compared with the values of the pin hole camera images according to EN 12543-2 and they deviated significantly. Several modifications of the evaluation method were proposed and a method with Integrated Line Profiles which produces results like an edge profile method was developed and tested providing similar results as the reference values. A second more simple method for end-users was introduced based on the evaluation of Penetrameter hole edges. A proposed update of the standards for focal spot measurements in ASTM and ISO is introduced. New classes will help the users to identify more simple and reliable the X-ray tube for their application.