IEC 60336:2020
(Main)Medical electrical equipment - X-ray tube assemblies for medical diagnosis - Focal spot dimensions and related characteristics
Medical electrical equipment - X-ray tube assemblies for medical diagnosis - Focal spot dimensions and related characteristics
IEC 60336:2020 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 document 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.
IEC 60336:2020 cancels and replaces the fourth edition published in 2005. This edition constitutes a technical revision.
The significant changes of this fifth edition with respect to the previous edition are detailed in Clause E.6. These changes are:
a) introduction of digital detectors and discretization errors;
b) fewer normative requirements;
c) support for both SLIT CAMERA and PINHOLE CAMERA;
d) reintroduction of distorted (skewed) FOCAL SPOT;
e) keeping of STAR PATTERNS and BLOOMING VALUE as informative.
The contents of the corrigendum of June 2022 have been included in this copy.
Appareils électromédicaux - Gaines équipées pour diagnostic médical - Dimensions des foyers et caractéristiques connexes
L'IEC 60336:2020 s’applique aux FOYERS des GAINES EQUIPEES à usage médical, pour diagnostic médical, fonctionnant à des POTENTIELS D’ACCELERATION DE TUBES RADIOGENES inférieurs ou égaux à 150 kV.
Le présent document décrit les méthodes d’essai ayant recours à des détecteurs numériques dans la détermination des:
a) dimensions des FOYERS en matière de VALEURS NOMINALES DE FOYER, variant de 0,1 à 3,0;
b) FONCTIONS DE DISTRIBUTION LINEAIRE;
c) FONCTIONS DE TRANSFERT DE MODULATION suivant une dimension;
d) RADIOGRAMMES A STENOPE,
et des moyens d’indiquer la conformité.
Les annexes informatives décrivent la MIRE ETOILE et la VALEUR DE DISPERSION.
L'IEC 60336:2020 annule et remplace la quatrième édition parue en 2005. Cette édition constitue une révision technique.
Les modifications majeures présentées dans cette cinquième édition par rapport à l’édition précédente sont énumérées dans l’Article E.6. Ces modifications sont:
a) introduction des détecteurs numériques et des erreurs de discrétisation;
b) exigences normatives moins nombreuses;
c) informations d’accompagnement relatives aux CAMERAS A FENTE et aux CAMERAS A STENOPE;
d) réintroduction de FOYER déformé (non linéaire);
e) conservation des MIRES ETOILES et de la VALEUR DE DISPERSION comme documents informatifs.
Le contenu du corrigendum de juin 2022 a été pris en considération dans cet exemplaire.
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IEC 60336 ®
Edition 5.0 2020-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Medical electrical equipment – X-ray tube assemblies for medical diagnosis –
Focal spot dimensions and related characteristics
Appareils électromédicaux – Gaines équipées pour diagnostic médical –
Dimensions des foyers et caractéristiques connexes
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IEC 60336 ®
Edition 5.0 2020-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Medical electrical equipment – X-ray tube assemblies for medical diagnosis –
Focal spot dimensions and related characteristics
Appareils électromédicaux – Gaines équipées pour diagnostic médical –
Dimensions des foyers et caractéristiques connexes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 11.040.50 ISBN 978-2-8322-9162-7
– 2 – IEC 60336:2020 © IEC 2020
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Determinations for the evaluation of the FOCAL SPOT characteristics . 9
4.1 Statement of the FOCAL SPOT characteristics . 9
4.2 Longitudinal axis of the X-RAY TUBE ASSEMBLY . 9
4.3 REFERENCE AXIS of the X-RAY TUBE ASSEMBLY . 9
4.4 Direction of evaluation for the FOCAL SPOT length . 9
4.5 Direction of evaluation for the FOCAL SPOT width . 10
4.6 Directions of evaluation for distorted FOCAL SPOTS. 10
5 FOCAL SPOT camera set-up . 10
5.1 Overview. 10
5.2 Diaphragm of the SLIT CAMERA . 10
5.3 Diaphragm of the PINHOLE CAMERA. 11
5.4 Receptor . 12
5.5 Test arrangement . 12
5.5.1 Position of the slit or pinhole diaphragm normal to the REFERENCE AXIS . 12
5.5.2 Position of the slit or pinhole diaphragm along the REFERENCE AXIS . 13
5.5.3 Orientation of the slit or pinhole diaphragm . 14
5.5.4 Position and orientation of the receptor of the DIGITAL FOCAL SPOT
DETECTOR. 14
5.6 Total uncertainty of the camera set-up . 15
6 Production of RADIOGRAMS . 16
6.1 Overview. 16
6.2 Operating conditions . 16
6.2.1 X-RAY TUBE ASSEMBLY . 16
6.2.2 LOADING FACTORS . 16
6.2.3 Special LOADING FACTORS . 17
6.2.4 Special arrangements . 17
6.3 Production of FOCAL SPOT SLIT RADIOGRAMS, FOCAL SPOT PINHOLE RADIOGRAMS
and FOCAL SPOT LINE SPREAD FUNCTIONS . 17
6.3.1 DIGITAL FOCAL SPOT DETECTOR requirements for FOCAL SPOT SLIT
RADIOGRAMS . 17
6.3.2 DIGITAL FOCAL SPOT DETECTOR requirements for FOCAL SPOT PINHOLE
RADIOGRAMS . 17
6.3.3 Determination of the RADIOGRAMS and of the LINE SPREAD FUNCTIONS . 18
6.4 Statement of compliance of the FOCAL SPOT PINHOLE RADIOGRAM. 18
6.5 Statement of compliance of LINE SPREAD FUNCTIONS . 18
7 Determination of FOCAL SPOT dimensions and NOMINAL FOCAL SPOT VALUES . 19
7.1 Overview. 19
7.2 Measurement and determination of FOCAL SPOT dimensions . 19
7.3 Specified NOMINAL FOCAL SPOT VALUEs . 19
7.3.1 Nominal values . 19
7.3.2 Actual dimensions . 20
7.4 Statement of compliance . 21
7.5 Marking of compliance . 21
8 Determination of the MODULATION TRANSFER FUNCTION . 22
8.1 Overview. 22
8.2 Calculation and presentation of the MODULATION TRANSFER FUNCTION . 22
8.3 Statement of compliance . 22
9 Alternative measurement methods for determining NOMINAL FOCAL SPOT VALUES . 23
Annex A (informative) Alignment to the REFERENCE AXIS . 24
Annex B (informative) FOCAL SPOT STAR RADIOGRAM . 26
B.1 Overview. 26
B.2 Test EQUIPMENT . 26
B.2.1 STAR PATTERN CAMERA . 26
B.2.2 RADIOGRAPHIC FILM . 27
B.2.3 Position of the STAR PATTERN CAMERA normal to the REFERENCE AXIS . 27
B.2.4 Position of the STAR PATTERN CAMERA in REFERENCE DIRECTION . 27
B.2.5 Alignment of the STAR PATTERN CAMERA . 27
B.2.6 Position of the RADIOGRAPHIC FILM . 28
B.2.7 Operating conditions . 28
B.2.8 Production of the FOCAL SPOT STAR RADIOGRAM . 28
Annex C (informative) STAR PATTERN RESOLUTION LIMIT . 29
C.1 Overview. 29
C.2 Measurement . 29
C.3 Determination of the STAR PATTERN RESOLUTION LIMIT . 30
C.3.1 Determination of the magnification . 30
C.3.2 STAR PATTERN RESOLUTION LIMIT for standard magnification . 30
C.3.3 STAR PATTERN RESOLUTION LIMIT for finite magnification . 30
C.3.4 Presentation of STAR PATTERN RESOLUTION LIMIT . 31
Annex D (informative) BLOOMING VALUE . 32
D.1 Overview. 32
D.2 Determination of the BLOOMING VALUE . 32
Annex E (informative) Historical background . 33
E.1 Overview. 33
E.2 First edition (1970) . 33
E.3 Second edition (1982) . 33
E.4 Third edition (1993) . 33
E.5 Fourth edition (2005) . 36
E.6 Fifth edition (2020) . 37
E.6.1 Overview . 37
E.6.2 Fifth edition technical details . 37
Bibliography . 42
Index of defined terms . 43
Figure 1 – Directions of evaluation over distorted FOCAL SPOTS . 10
Figure 2 – Essential dimensions of the slit diaphragm . 11
Figure 3 – Essential dimensions of the pinhole diaphragm . 12
Figure 4 – Position of the centre of the slit or pinhole diaphragm (marked as x in the
figure) with respect to the REFERENCE AXIS . 13
Figure 5 – Reference dimensions and planes . 14
– 4 – IEC 60336:2020 © IEC 2020
Figure 6 – Alignment of the receptor of the DIGITAL FOCAL SPOT DETECTOR with respect
to the slit diaphragm . 15
Figure 7 – LINE SPREAD FUNCTION . 19
Figure 8 – Graphical symbols – FOCAL SPOTS . 21
Figure A.1 – REFERENCE AXIS and directions of evaluation . 24
Figure A.2 – PROJECTION of the ACTUAL FOCAL SPOT on the IMAGE RECEPTION PLANE . 25
Figure B.1 – Essential dimensions of the star test pattern . 26
Figure B.2 – Alignment of the STAR PATTERN CAMERA . 27
Figure C.1 – Illustration of the zones of minimum modulation . 29
Figure E.1 – LSFs for a typical X-RAY TUBE with small FOCAL SPOT (< 0,3 mm) . 34
Figure E.2 – LSFs for a typical X-RAY TUBE with large FOCAL SPOT (≥ 0,3 mm) . 35
Figure E.3 – Corresponding MTFs for the LSFs in Figure E.2. 35
Figure E.4 – Percentage error of 15 % width . 38
Figure E.5 – Percentage error of LINE SPREAD FUNCTION width at 15 % . 39
Figure E.6 – Influence of the direction of evaluation on MTF-quality and on LINE SPREAD
width at 15 % . 40
FUNCTION
RADIOGRAMS . 15
Table 1 – Recommended enlargement for
Table 2 – LOADING FACTORS. 16
Table 3 – Maximum permissible values of FOCAL SPOT dimensions for NOMINAL FOCAL
SPOT VALUES . 20
Table C.1 – Standard magnifications for STAR PATTERN RESOLUTION LIMIT . 30
Table D.1 – LOADING FACTORS for the determination of the BLOOMING VALUE . 32
Table E.1 – Methods for evaluation of specific aspects characterising the FOCAL SPOT . 37
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEDICAL ELECTRICAL EQUIPMENT –
X-RAY TUBE ASSEMBLIES FOR MEDICAL DIAGNOSIS –
FOCAL SPOT DIMENSIONS AND RELATED CHARACTERISTICS
FOREWORD
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International Standard IEC 60336 has been prepared by subcommittee 62B: Diagnostic imaging
equipment, of IEC technical committee 62: Electrical equipment in medical practice.
This fifth edition cancels and replaces the fourth edition published in 2005. This edition
constitutes a technical revision.
The significant changes of this fifth edition with respect to the previous edition are detailed in
Clause E.6. These changes are:
a) introduction of digital detectors and discretization errors;
b) fewer normative requirements;
SLIT CAMERA and PINHOLE CAMERA;
c) support for both
d) reintroduction of distorted (skewed) FOCAL SPOT;
STAR PATTERNS and BLOOMING VALUE as informative.
e) keeping of
– 6 – IEC 60336:2020 © IEC 2020
The text of this document is based on the following documents:
CDV Report on voting
62B/1138/CDV 62B/1181/RVC
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
In this document, the following print types are used:
– requirements and definitions: roman type;
– informative material appearing outside of tables, such as notes, examples and references: in smaller type.
Normative text of tables is also in a smaller type;
– TERMS DEFINED IN CLAUSE 3 OF THIS DOCUMENT OR AS NOTED: SMALL CAPITALS.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it
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MEDICAL ELECTRICAL EQUIPMENT –
X-RAY TUBE ASSEMBLIES FOR MEDICAL DIAGNOSIS –
FOCAL SPOT DIMENSIONS AND RELATED CHARACTERISTICS
1 Scope
This document 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 document 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.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60417, Graphical symbols for use on equipment (available at http://www.graphical-
symbols.info/equipment)
IEC 60601-1:2005, Medical electrical equipment – Part 1: General requirements for basic safety
and essential performance
IEC 60601-1:2005/AMD1:2012
IEC 60601-1-3:2008, Medical electrical equipment – Part 1-3: General requirements for basic
safety and essential performance – Collateral Standard: Radiation protection in diagnostic X-
ray equipment
IEC 60601-1-3:2008/AMD1:2013
IEC 60613:2010, Electrical and loading characteristics of X-ray tube assemblies for medical
diagnosis
IEC TR 60788:2004, Medical electrical equipment – Glossary of defined terms
3 Terms and definitions
For the purposes of this document, terms and definitions given in IEC TR 60788:2004,
IEC 60613:2010, IEC 60601-1:2005 and IEC 60601-1:2005/AMD1:2012, IEC 60601-1-3:2008
and IEC 60601-1-3:2008/AMD1:2013 and the following apply.
– 8 – IEC 60336:2020 © IEC 2020
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
ACTUAL FOCAL SPOT
area on the surface of the TARGET that intercepts the beam of accelerated particles
Note 1 to entry: Regarding accelerated particles, only the intended primary beam is included.
3.2
BLOOMING VALUE
ratio of two resolution limits obtained under specific LOADING conditions
Note 1 to entry: The BLOOMING VALUE is a characteristic of the EFFECTIVE FOCAL SPOT of an X-RAY TUBE.
3.3
DIGITAL FOCAL SPOT DETECTOR
pixel-array device applied to FOCAL SPOT analysis of X-RAY TUBE ASSEMBLIES, providing a digital
output value per pixel which is linearly related to the input X-ray intensity
3.4
EFFECTIVE FOCAL SPOT
FOCAL SPOT
perpendicular PROJECTION of the ACTUAL FOCAL SPOT on the REFERENCE PLANE
3.5
FOCAL SPOT PINHOLE RADIOGRAM
RADIOGRAM obtained by means of a PINHOLE CAMERA, showing the shape and orientation of an
EFFECTIVE FOCAL SPOT, and the spatial distribution of intensity of radiation across it
3.6
FOCAL SPOT SLIT RADIOGRAM
RADIOGRAM obtained by means of a SLIT CAMERA, showing the distribution, across an EFFECTIVE
FOCAL SPOT, in the direction normal to the length of the slit, of the intensity of the radiation
emitted
3.7
FOCAL SPOT STAR RADIOGRAM
RADIOGRAM obtained by means of a STAR PATTERN CAMERA for the determination of the STAR
PATTERN RESOLUTION LIMIT in one or more directions across an EFFECTIVE FOCAL SPOT
3.8
NOMINAL FOCAL SPOT VALUE
dimensionless numerical value having a specific relation to the dimensions of the EFFECTIVE
FOCAL SPOT of an X-RAY TUBE, measured under specific conditions
3.9
PINHOLE CAMERA
assembly of EQUIPMENT used to obtain a FOCAL SPOT PINHOLE RADIOGRAM
3.10
REFERENCE AXIS
line in the REFERENCE DIRECTION through the centre of the RADIATION
SOURCE
3.11
REFERENCE DIRECTION
specified direction to which characteristics such as TARGET ANGLE,
RADIATION FIELD and specifications with respect to the imaging quality of the RADIATION SOURCE
are referenced
3.12
REFERENCE PLANE
plane perpendicular to the
REFERENCE DIRECTION containing the point at which the REFERENCE AXIS intersects with the
ACTUAL FOCAL SPOT
Note 1 to entry: By convention, the point of intersection forms the centre of the EFFECTIVE FOCAL SPOT.
3.13
SLIT CAMERA
assembly of EQUIPMENT used to obtain a FOCAL SPOT SLIT RADIOGRAM
3.14
STAR PATTERN CAMERA
assembly of EQUIPMENT used to obtain a FOCAL SPOT STAR RADIOGRAM
3.15
STAR PATTERN RESOLUTION LIMIT
characteristic of the FOCAL SPOT of an X-RAY TUBE, which represents the highest spatial
frequency that can be resolved under specific measuring conditions
3.16
TARGET
part of an X-RAY TUBE or a PARTICLE ACCELERATOR onto which is directed a beam of accelerated
particles to produce IONIZING RADIATION or other particles
4 Determinations for the evaluation of the FOCAL SPOT characteristics
4.1 Statement of the FOCAL SPOT characteristics
The FOCAL SPOT characteristics shall be stated for two normal directions of evaluation referred
to as the length direction and width direction. An illustration for Clause 4 can be found in Figure
A.1.
4.2 Longitudinal axis of the X-RAY TUBE ASSEMBLY
Generally, the longitudinal axis can be identified unambiguously. If the X-RAY TUBE ASSEMBLY
does not have an identifiable longitudinal axis or if it is specified otherwise by the
MANUFACTURER, the longitudinal axis shall be specified together with the FOCAL SPOT
characteristics.
4.3 REFERENCE AXIS of the X-RAY TUBE ASSEMBLY
If not specified otherwise, the REFERENCE AXIS is normal to the longitudinal axis and intersects
both the centre of the ACTUAL FOCAL SPOT and the longitudinal axis of the X-RAY TUBE ASSEMBLY.
4.4 Direction of evaluation for the FOCAL SPOT length
The direction of evaluation for the FOCAL SPOT length is normal to the REFERENCE AXIS in the
plane given by the REFERENCE AXIS and the longitudinal axis of the X-RAY TUBE ASSEMBLY.
NOTE The direction of evaluation for the FOCAL SPOT length is normally parallel to the longitudinal axis of the X-RAY
TUBE ASSEMBLY. See Figure A.1.
– 10 – IEC 60336:2020 © IEC 2020
4.5 Direction 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.
4.6 Directions of evaluation for distorted FOCAL SPOTS
If the PROJECTION of the EFFECTIVE FOCAL SPOT in the REFERENCE DIRECTION is distorted, the
direction of evaluation over the width may be chosen normal to the pronounced orientation of
the regions of highest radiation intensity, which is usually the direction over the FOCAL SPOT
showing the smallest width (see Figure 1).
Key
1 direction over the width
2 direction over the length
Figure 1 – Directions of evaluation over distorted FOCAL SPOTS
The direction of evaluation over the width of distorted FOCAL SPOTS shall not exceed ±20° from
the standard evaluation direction as specified in 4.5. If a direction of evaluation other than the
standard direction is used to determine the FOCAL SPOT width, then the value of this direction
shall be stated as part of the statement of compliance with this document. The angle of such
direction of evaluation is counted positive if the direction of evaluation has been rotated
clockwise, as seen from the FOCAL SPOT.
5 FOCAL SPOT camera set-up
5.1 Overview
Clause 5 deals with the design requirements of the camera: the diaphragm, the receptor and
the position and orientation of the diaphragm and the receptor.
5.2 Diaphragm of the SLIT CAMERA
The diaphragm of the SLIT CAMERA shall be made from materials with high ATTENUATION
properties and shall have dimensions as given in Figure 2.
Suitable materials are for example:
– tungsten;
– tantalum;
– alloy of gold and 10 % platinum;
– alloy of tungsten and 10 % rhenium;
– alloy of platinum and 10 % iridium.
Dimensions in millimetres
Key
1 axis of symmetry
Not drawn to scale.
Figure 2 – Essential dimensions of the slit diaphragm
5.3 Diaphragm of the PINHOLE CAMERA
The diaphragm of the PINHOLE CAMERA shall be constructed from materials with high
ATTENUATION and shall have dimensions as given in Figure 3.
Suitable materials are for example:
– tungsten;
– tantalum;
– alloy of gold and 10 % platinum;
– 12 – IEC 60336:2020 © IEC 2020
– alloy of tungsten and 10 % rhenium;
– alloy of platinum and 10 % iridium.
Dimensions in millimetres
Key
1 axis of symmetry
Not drawn to scale.
Figure 3 – Essential dimensions of the pinhole diaphragm
5.4 Receptor
The receptor is the X-RAY sensitive part of the DIGITAL FOCAL SPOT DETECTOR. The DIGITAL FOCAL
SPOT DETECTOR is a pixel-array device providing a digital output value per pixel which is linearly
related to the input X-ray intensity. Two types are specified for use in this document (see also
Figure 6):
– 1D-detector; the receptor consists of one pixel-array. This detector shall be applied to obtain
the FOCAL SPOT SLIT RADIOGRAMS (see 6.3.1).
NOTE The 1D-detector is sometimes referred to as "line-detector".
– 2D-detector; the receptor consists of a two-dimensional matrix of pixels. This detector may
be applied to obtain the FOCAL SPOT SLIT RADIOGRAMS (see 6.3.1), and it shall be applied to
obtain the FOCAL SPOT PINHOLE RADIOGRAM (see 6.3.2).
5.5 Test arrangement
5.5.1 Position of the slit or pinhole diaphragm normal to the REFERENCE AXIS
The slit or pinhole diaphragm shall be positioned in such a way that the distance from its centre
to the REFERENCE AXIS is within 0,2 mm per 100 mm of m (as indicated in Figure 4).
Key
1 EFFECTIVE FOCAL SPOT
2 REFERENCE AXIS
3 REFERENCE PLANE
4 incident face of the slit or pinhole diaphragm
5 IMAGE RECEPTION PLANE
Figure 4 – Position of the centre of the slit or pinhole diaphragm
(marked as x in the figure) with respect to the REFERENCE AXIS
5.5.2 Position of the slit or pinhole diaphragm along the REFERENCE AXIS
The incident face of the slit or pinhole diaphragm shall be placed at a distance from the
REFERENCE PLANE sufficient to ensure that the variation of the enlargement over the extension
of the ACTUAL FOCAL SPOT along the REFERENCE AXIS does not exceed ±5 %.
In Figure 5, the determining parameters are indicated, namely:
k is the distance from the REFERENCE PLANE to the edge of the ACTUAL FOCAL SPOT farthest
away from the slit or pinhole diaphragm;
p is the distance from the REFERENCE PLANE to the edge of the ACTUAL FOCAL SPOT closest to
the slit or pinhole diaphragm;
m is the distance from the REFERENCE PLANE to the incident face of the diaphragm;
n is the distance from the incident face of the diaphragm to the IMAGE RECEPTION PLANE;
E is the enlargement given by n/m.
NOTE Whether the requirement on the variation of the enlargement is met depends on the values of p, k and m –
whereas p and k depend in turn on the ANODE ANGLE and the ACTUAL FOCAL SPOT length. As an example, for m = 100,
maximum p and k is 5 mm.
– 14 – IEC 60336:2020 © IEC 2020
Key
1 ACTUAL FOCAL SPOT
2 REFERENCE AXIS
3 REFERENCE PLANE
4 incident face of the slit or pinhole diaphragm
5 IMAGE RECEPTION PLANE
Figure 5 – Reference dimensions and planes
5.5.3 Orientation of the slit or pinhole diaphragm
The axis of symmetry (see Figure 2 and Figure 3) shall be aligned with the REFERENCE AXIS
forming an angle that is smaller than 1°.
For the production of a pair of FOCAL SPOT SLIT RADIOGRAMS, the slit diaphragm shall be
orientated such that the length of the slit is normal to the direction of evaluation within ±1°.
5.5.4 Position and orientation of the receptor of the DIGITAL FOCAL SPOT DETECTOR
The receptor plane of the DIGITAL FOCAL SPOT DETECTOR (Figure 4 and Figure 5) shall be placed
normal to the REFERENCE AXIS within ±1°.
The enlargement E = n/m (Figure 4 and Figure 5) shall be determined with an accuracy to within
±3 %.
NOTE 1 For the choice of the enlargement, the following can be considered: with an infinitely narrow slit or pinhole,
a true image of the FOCAL SPOT would be obtained. However, the finite size of the slit or pinhole will broaden the
FOCAL SPOT image. Table 1 gives recommendations for the enlargement factor E. E is then larger for smaller FOCAL
SPOTS.
Table 1 – Recommended enlargement for RADIOGRAMS
NOMINAL FOCAL SPOT VALUE Enlargement
a b
(f) (E = n / m)
f ≤ 0,4 E ≥ 3
0,4 < f < 1,1 E ≥ 2
1,1 ≤ f E ≥ 1
a
See 7.3.
b
See Figure 4 and Figure 5.
The direction of evaluation for the FOCAL SPOT width or length shall be oriented normal to the
direction of the diaphragm slit to within ±1°. In Figure 6, such alignment of the diaphragm slit
and 1D-detector is indicated. Also, in Figure 6, for the 2D-detector, the output of such pixels is
combined to simulate the 1D-detector configuration.
NOTE Objects not to scale – for orientation only.
Figure 6 – Alignment of the receptor of the DIGITAL FOCAL SPOT DETECTOR
with respect to the slit diaphragm
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 small
enough to not influence the deduced NOMINAL FOCAL SPOT VALUES significantly.
NOTE 2 If the 1D-detector is not perfectly normal to the direction of the slit diaphragm, then the length of the pixel
will lead to an effective width of the pixel which is larger than the actual pixel-width. This effect can influence the
accuracy of the determination. It is good practice that the effective width of the pixel normal to the direction of the
slit diaphragm is not larger than twice the actual width of the pixel. The effective width of the pixels has a similar
effect on the accuracy as the aperture of the optical densitometer as applied in 7.2 of IEC 60336:2005. The
requirements for the aperture of the densitometer in IEC 60336:2005 are translated into this recommendation for the
effective pixel-width and for the alignment and length of the pixels.
5.6 Total uncertainty of the camera set-up
The total uncertainty of the camera set-up stems from the geometrical tolerances of the camera,
i.e.
a) position of the diaphragm normal to the REFERENCE AXIS (see 5.5.1);
– 16 – IEC 60336:2020 © IEC 2020
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 7.2) of the order of 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).
OADING FACTORS
6.2.2 L
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.
Table 2 – LOADING FACTORS
NOMINAL X-RAY Required X-RAY Exposure time Required X-RAY
TUBE VOLTAGE TUBE VOLTAGE TUBE power
kV
NOMINAL X-RAY 50 % of the NOMINAL
RADIOGRAPHY other
U < 75
TUBE VOLTAGE RADIOGRAPHIC
than COMPUTED
As a guideline see
ANODE INPUT POWER
TOMOGRAPHY
75 ≤ U ≤ 150 75 kV recommendations in
6.3.1 b) and c) or
120 kV 50 % of the NOMINAL
6.3.2 b) and c)
COMPUTED TOMOGRAPHY CT ANODE INPUT
POWER
6.2.3 Special LOADING FACTORS
If the LOADING FACTORS according to Table 2 do not fall 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 1 %.
a) The number of pixels o
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