This International Standard applies to FOCAL SPOTs in medical diagnostic X-RAY TUBE ASSEMBLIES for medical use, operating at X-RAY TUBE VOLTAGEs up to and including 150 kV. This International Standard describes the test methods employing digital detectors for determining: a). FOCAL SPOT dimensions in terms of NOMINAL FOCAL SPOT VALUES, ranging from 0,1 to 3,0; b). LINE SPREAD FUNCTIONS; c). one-dimensional MODULATION TRANSFER FUNCTIONS; d). FOCAL SPOT PINHOLE RADIOGRAMS, and the means for indicating compliance. In informative annexes, STAR PATTERN imaging and BLOOMING VALUE are described.