This document specifies a method for the measurement of focal spot dimensions within the range of 5 µm to 300 µm of X-ray systems up to and including 225 kV tube voltage. This determination is based on the evaluation of an image with a dedicated focal spot that has been radiographically recorded using an edge and evaluated with a digital method. The imaging quality and the resolution of X-ray images depend highly on the characteristics of the effective focal spot, in particular the size and the two-dimensional intensity distribution as seen from the detector plane. For the characterisation of commercial X-ray tube types (i.e. for advertising or trade) the specific maximum values of annex A should be preferred.
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