This International Standard is applicable to X-RAY SOURCE ASSEMBLIES and X-RAY TUBE ASSEMBLIES, for use in MEDICAL DIAGNOSTIC RADIOLOGY for techniques in which the X-RAY PATTERN will be received simultaneously in all points of the IMAGE RECEPTION AREA. This standard specifies a method for the determination of the greatest geometrically symmetrical RADIATION FIELD at a specified distance from the FOCAL SPOT for which the percentage AIR KERMA RATE along the major axes of the RADIATION FIELD does not fall below a permitted value. NOTE 1 AIR KERMA or AIR KERMA RATE are the only practical verifiable physical quantities for X-RAY SOURCES. X-RAY SOURCES must be tested independently from MEDICAL ELECTRICAL SYSTEMS. Conversion to the characteristics of the X-RAY IMAGE RECEPTOR used in a MEDICAL ELECTRICAL SYSTEM may be done in addition. In case multiple FOCAL SPOTS are not super-imposed, each focal spot has its own REFERENCE AXIS. Then the maximum RADIATION FIELD may be given for each FOCAL SPOT separately NOTE 2 The maximum symmetrical RADIATION FIELD may change from its initial value as the X-RAY TUBE ages through use. NOTE 3 If, for certain MEDICAL ELECTRICAL SYSTEMs the scope of IEC 60806 does not fit, then the special RADIATION FIELD requirements could be incorporated in the MEDICAL ELECTRICAL SYSTEM particular standard. However, a statement on the RADIATION FIELD while referring IEC 60806 is then no longer possible.