X-ray tube assemblies for medical diagnosis — Focal spot dimensions and related characteristics
IEC 60336-2020 pdf download.Medical electrical equipment — X-ray tube assemblies for medical diagnosis — Focal spot dimensions and related characteristics
Appareils électromédicaux — Gaines équipees pour diagnostic medical — Dimensions des foyers et caracteristiques connexes.
b) position of the diaphragm along the REFERENCE AXIS (see 5.5.2);
c) alignment of the axis of symmetry of the diaphragm with the REFERENCE AXIS (see 5.5.3);
d) position (distance and perpendicularity) of the DIGITAL FOCAL SPOT DETECTOR (see 5.5.4).
NOTE The typical total uncertainty of the camera set-up will lead to an error in the width of the LINE SPREAD FUNCTION deduced from the FOCAL SPOT SLIT RADIOGRAM (see 72) of the order or 5 %.The MANUFACTURER can choose a different set of geometrical tolerances, as long as the requirement in Clause 9 is met.
6 Production of RADIOGRAMS
6.1 Overview
Clause 6 deals with production of FOCAL SPOT SLIT RADIOGRAMS and FOCAL SPOT PINHOLE RADIOGRAMS, which shall be produced using a FOCAL SPOT camera according to Clause 5, while following the operating conditions in 6.2 and 6.3.
NOTE Adequate shielding Is usually needed to minimize the effect of STRAY RADIATION on the RADIOGRAM. FOCAL SPOT PINHOLE RADIOGRAMS have an informative character only. for showing the
distribution of radiant intensity over the FOCAL SPOT.
The method of indicating compliance with this document of FOCAL SPOT RADIOGRAMS is described in 6.4. The method of indicating compliance with this document of LINE SPREAD FUNCTIONS is described in 6.5,
6.2 Operating conditions
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 specified for NORMAL USE or it shall be placed under equivalent mounting and operating conditions as far as these can influence the results of the test.
All the materials belonging to the X-RAY TUBE ASSEMBLY in NORMAL USE shall be installed. No ADDITIONAL FILTRATION shall be used to decrease the X-ray output flux unless it is verified that the ADDITIONAL FILTRATION has no significant effect on the LINE SPREAD FUNCTION (see 6.3.3).
6.2.2 LOADING FACTORS
FOCAL SPOT SLIT RADIOGRAMS or FOCAL SPOT PINHOLE RADIOGRAMS for X-RAY TUBE ASSEMBLIES used in PROJECTION RADIOGRAPHY or in COMPUTED TOMOGRAPHY shall be obtained with constant LOADING FACTORS in accordance with Table 2.
6.2.3 Special LOADING FACTORS
If the LOADING FACTORS according to Table 2 do not tall within the RADIOGRAPHIC RATINGS for the X-RAY TUBE concerned or if they otherwise do not cover the typical special applications of specified NORMAL USE of the X-RAY TUBE. LOADING FACTORS shall be chosen to correspond to those specific conditions. In this case, the LOADING FACTORS under which the FOCAL SPOT SLIT RADIOGRAMS or FOCAL SPOT PINHOLE RADIOGRAMS were obtained shall be stated in the statement of compliance together with the characteristics.
In particular cases, it may be appropriate to state the characteristics of a FOCAL SPOT under additional LOADING conditions.
6.2.4 Special arrangements
If, for the purpose of production of suitable FOCAL SPOT SLIT RADIOGRAMS, arrangements were made for the adjustment and alignment of either the SLIT CAMERA or X-RAY TUBE ASSEMBLY, or if special electrical or LOADING conditions prevailed, details shall be stated together with the characteristics in the statement of compliance.
6.3 Production of FOCAL SPOT SLIT RADIOGRAMS, FOCAL SPOT PINHOLE RADIOGRAMS and
FOCAL SPOT LINE SPREAD FUNCTIONS
6.3.1 DIGITAL FOCAL SPOT DETECTOR requirements for FOCAL SPOT SLIT RADIOGRAMS
The spatial range of the FOCAL SPOT SLIT RADIOGRAM shall be such that further extension of the spatial range does not significantly change the result for the 15 % width.
NOTE In general, the spatial range of three times the 15 % width of the LINE SPREAD FUNCTION IS sufficient.
Discretization errors are Inherent to digital detectors and the subsequent signal processing.
These errors will lead to LINE SPREAD FUNCTION widths which are larger than in the ideal case.
The following choice of parameters is recommended in order to limit the error induced by
discretization to about I %.
a) The number of pixels over the 15 % width of the LINE SPREAD FUNCTION is at least 30, and linear interpolation is applied. If linear interpolation is not applied, the number of pixels should be at least 60.
b) The number of levels between the background level and the maximum signal of the LINE SPREAD FUNCTION is 200 or more.
c) The signal to noise ratio is 200 or better.
See also E.6.2 a).
6.3.2 DIGITAL FOCAL SPOT DETECTOR requirements for FOCAL SPOT PINHOLE RADIOGRAMS.IEC 60336-2020 pdf download.