IEC 62945:2018

IEC 62945 ®
Edition 1.0 2018-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Radiation protection instrumentation – Measuring the imaging performance of
X-ray computed tomography (CT) security-screening systems

Instrumentation pour la radioprotection – Mesure des performances d'imagerie
des systèmes de contrôle de sécurité utilisant la tomographie par ordinateur
(CT) à rayons X
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IEC 62945 ®
Edition 1.0 2018-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Radiation protection instrumentation – Measuring the imaging performance of

X-ray computed tomography (CT) security-screening systems

Instrumentation pour la radioprotection – Mesure des performances d'imagerie

des systèmes de contrôle de sécurité utilisant la tomographie par ordinateur

(CT) à rayons X
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.280 ISBN 978-2-8322-6025-8

– 2 – IEC 62945:2018 © IEC 2018
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references. 9
3 Terms and definitions, abbreviated terms, quantities and units . 9
3.1 Terms and definitions . 9
3.2 Abbreviated terms . 12
3.3 Quantities and units . 12
4 Imaging performance evaluation procedures . 12
4.1 General test performance requirements . 12
4.2 Description of test articles . 13
4.3 Manually recorded data . 16
4.3.1 Purpose . 16
4.3.2 System data . 16
4.3.3 Evaluation environment data . 18
4.3.4 Comments . 18
4.3.5 Deviations from specified methods . 18
4.3.6 Presentation of results . 19
4.4 Object length accuracy . 20
4.4.1 Purpose . 20
4.4.2 Test object description . 21
4.4.3 Test method . 21
4.4.4 Presentation of results . 23
4.5 Path-length CT value and Z . 24
eff
4.5.1 Purpose . 24
4.5.2 Test object description . 24
4.5.3 Test method . 25
4.5.4 Presentation of results . 26
4.6 Noise equivalent quanta (NEQ) . 26
4.6.1 Purpose . 26
4.6.2 Test object description . 27
4.6.3 Test method . 27
4.6.4 Presentation of results . 29
4.7 CT value consistency . 30
4.7.1 Purpose . 30
4.7.2 Test object description . 30
4.7.3 Test method . 30
4.7.4 Presentation of results . 30
4.8 CT value uniformity and x-ray energy spectrum consistency . 30
4.8.1 Purpose . 30
4.8.2 Test object description . 31
4.8.3 Test method . 31
4.8.4 Presentation of results . 32
4.9 Streak artifacts . 33
4.9.1 Purpose . 33
4.9.2 Test object description . 33

4.9.3 Test method . 33
4.9.4 Presentation of results . 34
4.10 Slice sensitivity profile (SSP) . 35
4.10.1 Purpose . 35
4.10.2 Test object description . 35
4.10.3 Test method . 35
4.10.4 Presentation of results . 36
4.11 Image registration . 36
4.11.1 Purpose . 36
4.11.2 Test object description . 36
4.11.3 Test method . 37
4.11.4 Presentation of results . 40
5 Environmental requirements. 40
Annex A (normative) Detailed test article specifications and drawings . 41
A.1 General . 41
A.2 Commercial parts . 41
A.3 Outer enclosure . 41
A.4 Detailed drawings of custom components . 42
Annex B (informative) Example of reporting format . 66
B.1 General . 66
B.2 Example report . 66
Annex C (informative) Statistical guidance on multiple scans, summary statistics, and
comparison of results . 70
C.1 General . 70
C.2 Scenario A: Comparing a single CT system between its baseline and
candidate (revised) configuration . 70
C.3 Scenario B: Comparing a single (candidate) system against an existing
historical population of systems . 71
Bibliography . 72

Figure 1 – Reference axes for testing procedures . 13
Figure 2 – Test article A . 14
Figure 3 – Test article B . 15
Figure 4 – Format example for manually recorded data . 20
Figure 5 – Object length test object . 21
Figure 6 – Output from object length procedure when test article is submitted within
angular tolerance . 24
Figure 7 – Output from object length procedure when test article rotation is outside of
angular tolerance . 24
Figure 8 – Path-length test object . 25
Figure 9 – Example plot of path-length test results . 26
Figure 10 – NEQ test object . 27
Figure 11 – Z uniformity test object and streak artifact test object . 31
Figure 12 – Pins in test object axial slice (large circle), midpoints between neighboring
pin pairs (small circles), traced line, and rectangular ROI. 33
Figure 13 – Slanted edge test object used to measure z resolution . 35
Figure 14 – Registration test object (not to scale) . 37

– 4 – IEC 62945:2018 © IEC 2018
Figure 15 – CT image of registration test object, slice plane 1 . 38
Figure 16 – Horizontal line profile through CT slice of the registration test object . 38
Figure 17 – Projection image of the registration test object and vertical profile through
image . 39
Figure A.1 – Assembly of Case A test article . 43
Figure A.2 – Assembly of Case B test article . 44
Figure A.3 – Test component sub-assembly of Case A test article (drawing 1 of 2) . 45
Figure A.4 – Test component sub-assembly, Case A test article (drawing 2 of 2) . 46
Figure A.5 – Test component sub-assembly, Case B test article (drawing 1 of 2) . 47
Figure A.6 – Test component sub-assembly, Case B test article (drawing 2 of 2) . 48
Figure A.7 – Sub-components for Case A cylinder test object . 49
Figure A.8 – Ring sub-components for Case A cylinder test object . 50
Figure A.9 – Pin sub-components for Case A cylinder test object (streak artifacts) . 51
Figure A.10 – Al sub-component for image registration test object, Case A . 52
Figure A.11 – POM sub-components for image registration test object, Case A . 53
Figure A.12 – Cylinder test object (NEQ and CT value consistency), Case B . 54
Figure A.13 – Object length test object, Cases A and B . 55
Figure A.14 – Path length test object, Case A . 56
Figure A.15 – SSP test object, Case B . 57
Figure A.16 – Partition panel for component support, Cases A and B (drawing 1 of 4) . 58
Figure A.17 – Partition panel for component support, Case A (drawing 2 of 4) . 59
Figure A.18 – Partition panel for component support, Case B (drawing 3 of 4) . 60
Figure A.19 – Partition panel for component support, Case B (drawing 4 of 4) . 61
Figure A.20 – Component support rods, Cases A and B . 62
Figure A.21 – Assembly washers, Cases A and B . 63
Figure A.22 – Sub-assembly for Case A cylinder test object . 64
Figure A.23 – Sub-assembly for Case A image registration test object . 65

Table 1 – List of test methods and indicators measured . 16
Table 2 – NEQ procedure results . 29
Table 3 – CT value uniformity results . 32
Table 4 – Streak artifact procedure results . 34
Table 5 – SSP procedure results . 36
Table A.1 – Commercial foils required for fabrication of CT value uniformity and x-ray
energy spectrum consistency test object (4.8) . 41

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RADIATION PROTECTION INSTRUMENTATION –
MEASURING THE IMAGING PERFORMANCE OF X-RAY
COMPUTED TOMOGRAPHY (CT) SECURITY-SCREENING SYSTEMS

FOREWORD
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62945 has been prepared by subcommittee 45B: Radiation
protection instrumentation, of IEC technical committee 45: Nuclear instrumentation.
The text of this International Standard is based on the following documents:
FDIS Report on voting
45B/908/FDIS 45B/910/RVD
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.

– 6 – IEC 62945:2018 © IEC 2018
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.
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understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
This document establishes standard test methods and test objects for measuring the imaging
performance of x-ray computed tomography (CT) security-screening systems. The quality of
data for automated analysis is the primary concern. This document does not address the
system’s ability to use its image data to automatically detect explosives or other threat
materials, which is typically verified by an appropriate regulatory body.
Three annexes are included. Annex A (normative) provides mechanical drawings of the
imaging test objects that compose the test article. A sample test report form is given in Annex
B (informative). Annex C (informative) offers statistical guidance on multiple scans, summary
statistics, and comparison of results. Finally, a bibliography is given (informative).

– 8 – IEC 62945:2018 © IEC 2018
RADIATION PROTECTION INSTRUMENTATION –
MEASURING THE IMAGING PERFORMANCE OF X-RAY
COMPUTED TOMOGRAPHY (CT) SECURITY-SCREENING SYSTEMS

1 Scope
This document provides test methods for the evaluation of image quality of computed
tomography (CT) security-screening systems. The quality of data for automated analysis is
the primary concern. This document does not address the system’s ability to use this image
data to automatically detect explosives or other threat materials, nor is it intended for vendor-
to-vendor comparisons of threat-detection performance.
Security screening systems are generally used to scan parcels, including luggage, for the
presence of illicit items such as explosives, drugs, or other contraband. Many of the screening
systems currently used, particularly in transportation security applications, are based on CT
imaging technology. Generally, as the parcel is transported through the system, the system
collects a CT image of the parcel. These data are then subjected to automated analysis to
determine whether a threat may be present or the parcel is considered clear. If the automated
analysis determines a threat may be present, the image is often presented to a system
operator who can override the automated decision, clearing the parcel, or referring it for
further processing such as opening it and manually searching for threats.
Historically, government regulators have established evaluation procedures to determine
whether a system’s automated detection performance is adequate for use in applications
within their borders. Typically, a vendor submits a copy of their product, including their
software to the regulator’s facility. The regulator runs a wide variety of parcels with threats
inside through the system as well as parcels without threats that represent the typical stream
of commerce. Detection and false alarm rates are determined and compared against
performance criteria. If the criteria are met, the system is approved for use. This testing
ensures that the system is capable of meeting the required criteria, but how does one ensure
that all copies of the system meet the criteria? Normal manufacturing variability, quality
control issues, or aging of the equipment may degrade performance versus what was
observed on the article tested by the regulator. Replicating the original test on each machine
in question is impractical. Transporting the regulator’s threat set to a factory site or to
locations where the machines are in use presents significant security and in some cases
safety concerns. This document seeks to address this issue by specifying a suite of test
methods that can be carried out on site without need for hazardous materials.
The performance testing carried out by the regulators essentially evaluates the combination of
the system’s ability to produce an image of the parcel along with its automatic analysis of that
image data to reach a decision of threat or clear. The second part of this sequence, the
analysis, is implemented through software. Regulators generally require that this software be
designed so as to not evolve through use. The software used at all locations in the field must
perform the same as the software did at the time of evaluation by the regulator. Configuration
management of such software is a well-known and straightforward art. Therefore, the real
opportunity for performance variation comes from the imaging system that provides the data
to the analysis software. If one can quantitatively validate that the quality of the image
produced by the system in question is statistically equivalent to the image produced by the
article evaluated by the regulator, one can be highly confident that the performance of the
system in question is the same as what was approved by the regulator.
Purchasers of CT systems for security screening applications are generally not CT experts.
Inconsistencies in methods for measuring seemingly standard image quality values (resolution,
signal-to-noise, etc.) can confuse the potential user of such CT systems. Other standards
exist for testing aspects of CT image quality, particularly in the medical field. This document
specifies a set of methods to apply in assessing CT image quality geared towards security

screening. An application of this document would be in the factory acceptance testing of
equipment. The document could be used to indicate whether the unit offered for sale
produces the equivalent image quality as the unit that was tested by the cognizant regulatory
agency. Since various image quality metrics can be traded off against one another and
achieve similar levels of threat detection, it is generally not valid, in contrast to medical CT, to
make model-to-model or manufacturer-to-manufacturer comparisons of individual test results
for CT systems used for security-screening.
This document does not address image quality presented to the operator. The image quality
provided to the operator is not necessarily at the same level as that used by the automated
analysis. The data may be degraded before presenting to the operator to decrease resources
required for rendering the image on the screen. Conversely, the data used in the automated
analysis may be intentionally degraded to control the computational loading of the analysis
computer. The user of this document may want to separately assess the quality of the images
presented to the system’s operator. A wide range of methods is available for this purpose
including the use of visual line pair gauges and ASTM F792 [1].
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 60050-395:2014, International Electrotechnical Vocabulary – Part 395: Nuclear
instrumentation: Physical phenomena, basic concepts, instruments, systems, equipment and
detectors
IEC 60050-881, International Electrotechnical Vocabulary. Radiology and radiological physics
ASTM E1695, Standard Test Method for Measurement of Computed Tomography (CT) System
Performance
ASTM publications are available from the ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA
19428-2959, USA (http://www.astm.org/).
ASTM D6100, Standard Specification for Extruded, Compression Molded and Injection Molded
Polyoxymethylene Shapes (POM)
SAE AMS 4027: Aluminum Alloy, Sheet and Plate, 1.0Mg – 0.60Si – 0.28Cu – 0.20Cr (6061; -
T6 Sheet, -T651 Plate), Solution and Precipitation Heat Treated
SAE AMS 4117: Aluminum Alloy, Rolled or Cold Finished Bars, Rods, and Wire and Flash
Welded Rings, 1.0Mg – 0.60Si – 0.28Cu – 0.20Cr, (6061; -T6, -T651), Solution and
Precipitation Heat Treated
3 Terms and definitions, abbreviated terms, quantities and units
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply. The general
terminology concerning x-ray systems and radiological physics is given in IEC 60050-395 and
IEC 60050-881.
___________
Numbers in square brackets refer to the Bibliography.

– 10 – IEC 62945:2018 © IEC 2018
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
3.1.1
computed tomography
CT
process of rendering a three-dimensional image of a volume based on x-ray projection data
3.1.2
CT value
value reported by CT systems on a per voxel basis that is a function of the material’s density
and atomic number
3.1.3
coronal image
two-dimensional image produced by summing a three-dimensional volume image along the y-
axis
Note 1 to entry: Axes defined in Figure 1.
3.1.4
effective atomic number
Z
eff
material property that represents the atomic number of a theoretical element that, if the
material were replaced by the element, would produce the same x-ray attenuation
characteristics
Note 1 to entry: Z measurements can be scanner-dependent and should not be considered absolute values.
eff
3.1.5
mean
for n quantities, x , x , … x , the quotient of the sum of the quantities by n:
1 2 n
𝑛𝑛
𝑥𝑥̅= � 𝑥𝑥
𝑖𝑖
𝑛𝑛
𝑖𝑖=1
3.1.6
modulation transfer function
MTF
frequency-dependent measure of an imaging system’s resolution or ability to reproduce object
contrast. In one dimension it is computed from the system's response to an edge of high
contrast using ASTM E1695
3.1.7
multi-energy
x-ray imaging system that collects image data at more than one x-ray energy spectrum
Note 1 to entry: This can be accomplished, for example, by varying the x-ray tube voltage, using an energy
discriminating detector, or using multiple sets of detectors with differing energy response.

3.1.8
noise equivalent quanta
NEQ
spatial-frequency-dependent measure of noise, interpreted as the number of quanta (radiation
exposure) that an ideal detector would have needed to yield the same signal-to-noise ratio as
an actual imaging system. It is computed from measurements of average CT value in an
imaged object, the system’s modulation transfer function and noise power spectrum
3.1.9
noise power spectrum
NPS
spatial-frequency-dependent variance of an imaging system’s noise, computed using the
Fourier transform of uniform noise-limited images
3.1.10
projection image
x-ray image created by detecting the x-ray intensity transmitted through the subject, resulting
in an image in which all the subject’s components appear to be projected onto a single image
plane
3.1.11
registration
spatial relationship between the coordinate systems of multiple imaging subsystems. It
determines the ability to accurately correlate observations from one image to the others
3.1.12
slice
cross-sectional image of the inspected object
Note 1 to entry: The normal of the plane of the image is in the direction of the conveyer belt motion (z axis).
3.1.13
slice sensitivity profile
SSP
frequency-dependent measure of CT image resolution along the direction of the conveyer belt
motion (z axis)
3.1.14
standard deviation
sample standard deviation, σ , of n quantities, x , x , … x given by:
n 1 2 n
𝑛𝑛 2
𝜎𝜎 = � ∑ (𝑥𝑥 −𝑥𝑥̅) where 𝑥𝑥̅ is given by 3.1.5
𝑛𝑛 𝑖𝑖
𝑖𝑖=1
𝑛𝑛−1
3.1.15
standard mode of operation
mode of operation normally recommended by the manufacturer for inspection of parcels
Note 1 to entry: Some systems have special modes for collecting extra data for training. This would not be
considered a standard mode of operation.
3.1.16
test article
item, to be imaged by the system, containing multiple test objects in a specific geometric
layout
Note 1 to entry: As used in this document, test article refers to the specific items defined in 4.2.

– 12 – IEC 62945:2018 © IEC 2018
3.1.17
test object
individual object having specific properties (size, shape, materials, etc.) that when imaged by
the system allows a certain image quality evaluation to be carried out
3.1.18
voxel
volume element representing a rectangular prism-shaped region in space within a volumetric
image
3.2 Abbreviated terms
CT computed tomography
MTF modulation transfer function
NEQ noise equivalent quanta
NPS noise power spectrum
POM polyoxymethylene
NOTE POM is the acetal copolymer (CH O) of which the test objects of this document are fabricated.
2 n
ROI region of interest (in an image)
SNR signal-to-noise ratio
SSP slice sensitivity profile
3.3 Quantities and units
In this document, the units are the multiples and sub-multiples of units of the International
System of Units (SI) [2]. The definitions of radiation quantities are given in
IEC 60050-395:2014.
The following units may also be used:
–19
• for energy: electron-volt (symbol: eV), 1 eV = 1,602 x 10 J;
• for time: years (symbol: y), days (symbol: d), hours (symbol: h), minutes (symbol: min):
• for temperature: degrees Celsius (symbol: ºC), 0 ºC = 273,15 K.
Multiples and submultiples of SI units are used, when practicable, according to the SI system.
4 Imaging performance evaluation procedures
4.1 General test performance requirements
System components and adjustments should be as for the standard commercial product in
normal security screening operation mode; any deviations shall be noted by the evaluators in
the manually recorded data. If the system is approved to operate under more than one
configuration, the user may want to request the test be carried out at all appropriate settings.
Evaluation is to be based on images or other data normally used in standard mode of
operation. The exposure time and level shall be chosen as that used when the CT system is
operated for the intended use in the security screening application. A calibration of the CT
system shall be carried out prior to any testing. Any recalibration of the CT system shall be
allowed according to the standard operation of the system. In order to ensure that the system
is using a configuration approved by the appropriate regulatory agency, the user may wish to
request that the vendor provide the specific settings used during the evaluation such as: tube
voltage(s), amperage, voxel size, belt speed, etc. Changes in CT image reconstruction
software should be followed by gathering a new baseline measurement set. Alternatively, new
baseline results may be recomputed offline if the data are available.

The test articles (see 4.2) shall be presented to the system in a controlled position and
orientation. The main axis of each test article should be parallel to the conveyor belt motion
direction and the front of the article shall enter the system first (front designated via labeling).
The test method described in 6.3 determines the angle of rotation and side to side offset of
the test articles relative to the centerline of the system conveyor. Results for rotations more
than 2 degrees off parallel from conveyor centerline shall be rejected. This document requires
that the test articles be measured at the center of the belt, directly on the belt, within ± 2 cm
of the conveyor centerline. If the user decides to also run the test articles off centerline, the
parallel requirement shall still be met, and the data shall be segregated and treated
separately.
For reference, Figure 1 shows the coordinate system that shall be used for all procedure
descriptions. The z axis is aligned along the direction of the conveyor motion. The y axis is in
the vertical direction and the x axis is across the belt. The positive/negative direction of the
axis system is immaterial as used in this document.
Not all the methods stated are applicable to all CT systems. Each method shall identify
whether it is applicable to all CT types or only a subset.
Each of the test methods specified in this document can include required procedures and
examples of optional techniques for achieving the required results. This is necessary because
of the range of implementations used in security CT equipment. Each test method identifies
where latitude for deviation from the analysis techniques exists. Any deviation from provided
example techniques shall be documented including rationale for deviating from the suggested
standard method of analysis. Such documentation shall be provided to the end user of the
image quality evaluation.
Y
X
Z
IEC
Figure 1 – Reference axes for testing procedures
4.2 Description of test articles
Execution of this document requires two test articles. They are designated “test article A” and
“test article B,” and are represented in Figure 2 and Figure 3. The articles consist of several
test objects supported in a machined frame within a commercial or custom-built carrying case.

– 14 – IEC 62945:2018 © IEC 2018
The placement of the test objects has been selected to minimize artifacts from one test object
interfering with the image of another test object.
When fabricating test articles for use in this document, the test objects and the supporting
structural frame shall be built in accordance with the detailed drawing package included in
Annex B. The outer case should be selected for durability. It shall be large enough to contain
the specified support structure. If commercial encasements are used, they may need to be
modified to remove any metal structures (hinges, handles, fasteners, etc.) from the sides, top
and bottom. Removing structures on the front and back surfaces (facing the z direction) is
optional. If a commercial case is used, it shall be modified to remove any significant plastic
structure along the sides, top, and bottom that might interfere with the imaging of the test
object. Comparison of testing results, across time for example,
...