IEC 60336:2020 pdf free download – Medical electrical equipment – X-ray tube assemblies for medical diagnosis
4.5Direction of evaluation for the FoCAL SPoT width
The direction of evaluation for the FOCAL SPOT width is normal to the longitudinal axis of the X-RAY TUBE ASSEMBLY and normal to the REFERENCE AXIS.
4.6Directions of evaluation for distorted FOCAL SPOTs
lf the PROJECTION of the EFFECTIVE FOCAL SPoT in the REFERENCE DIRECTION is distorted, thedirection of evaluation over the width may be chosen normal to the pronounced orientation ofthe regions of highest radiation intensity，which is usually the direction over the FocAL SPOTshowing the smallest width (see Figure 1).
The direction of evaluation over the width of distorted FOCAL SPOTs shall not exceed ±20° fromthe standard evaluation direction as specified in 4.5. lf a direction of evaluation other than thestandard direction is used to determine the FocAL SPoT width, then the value of this directionshall be stated as part of the statement of compliance with this document.The angle of suchdirection of evaluation is counted positive if the direction of evaluation has been rotatedclockwise, as seen from the FOCAL SPOT.
NOTE 1 As presented in Figure 6, the direction of the arrays of the 2D-detector is not critical, as with a well-designed detector, following the recommendations for the number of pixels in 6.3.1 and 6.3.2 the pixels are smallenough to not influence the deduced NOMINAL FOCAL SPOT VALuEs significantly.
NOTE 2 lf the 1D-detector is not perfectly normal to the direction of the slit diaphragm, then the length of the pixelwill lead to an effective width of the pixel which is larger than the actual pixel-width. This effect can influence theaccuracy of the determination. lt is good practice that the effective width of the pixel normal to the direction of theslit diaphragm is not larger than twice the actual width of the pixel. The effective width of the pixels has a similareffect on the accuracy as the aperture of the optical densitometer as applied in 7.2 of IEC 60336:2005.Therequirements for the aperture of the densitometer in lEC 60336:2005 are translated into this recommendation for theeffective pixel-width and for the alignment and length of the pixels.
6.2.1 X-RAY TUBE ASSEMBLY
The X-RAY TUBE shall be installed in an X-RAY TUBE HOUSING of the type for which it is specifiedfor NORMAL USE or it shall be placed under equivalent mounting and operating conditions as faras these can influence the results of the test.
All the materials belonging to the X-RAY TUBE ASSEMBLY in NORMAL USE shall be installed.NoADDITIONAL FILTRATION shall be used to decrease the X-ray output flux unless it is verified thatthe ADDITIONAL FILTRATION has no significant effect on the LINE SPREAD FUNCTION (see 6.3.3).