SIST EN ISO 15708-3:2025

SLOVENSKI STANDARD
01-oktober-2025
Neporušitvene preiskave - Sevalne metode za računalniško tomografijo - 3. del:
Delovanje in razlaga (ISO 15708-3:2025)
Non-destructive testing - Radiation methods for computed tomography - Part 3:
Operation and interpretation (ISO 15708-3:2025)
Zerstörungsfreie Prüfung - Durchstrahlungsverfahren für Computertomographie - Teil 3:
Durchführung und Auswertung (ISO 15708-3:2025)
Essais non destructifs - Méthodes par rayonnements pour la tomographie informatisée -
Partie 3: Fonctionnement et interprétation (ISO 15708-3:2025)
Ta slovenski standard je istoveten z: EN ISO 15708-3:2025
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 15708-3
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2025
EUROPÄISCHE NORM
ICS 19.100 Supersedes EN ISO 15708-3:2019
English Version
Non-destructive testing - Radiation methods for computed
tomography - Part 3: Operation and interpretation (ISO
15708-3:2025)
Essais non destructifs - Méthodes par rayonnements Zerstörungsfreie Prüfung - Durchstrahlungsverfahren
pour la tomographie informatisée - Partie 3: für Computertomographie - Teil 3: Durchführung und
Fonctionnement et interprétation (ISO 15708-3:2025) Auswertung (ISO 15708-3:2025)
This European Standard was approved by CEN on 15 June 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

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Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15708-3:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 15708-3:2025) has been prepared by Technical Committee ISO/TC 135 "Non-
destructive testing " in collaboration with Technical Committee CEN/TC 138 “Non-destructive testing”
the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by January 2026, and conflicting national standards shall
be withdrawn at the latest by January 2026.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 15708-3:2019.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 15708-3:2025 has been approved by CEN as EN ISO 15708-3:2025 without any
modification.
International
Standard
ISO 15708-3
Second edition
Non-destructive testing —
2025-06
Radiation methods for computed
tomography —
Part 3:
Operation and interpretation
Essais non destructifs — Méthodes par rayonnements pour la
tomographie informatisée —
Partie 3: Fonctionnement et interprétation
Reference number
ISO 15708-3:2025(en) © ISO 2025

ISO 15708-3:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 15708-3:2025(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Operational procedure . 1
4.1 General .1
4.2 CT system set-up .2
4.2.1 General .2
4.2.2 Geometry .2
4.2.3 X-ray source .3
4.2.4 Detector .3
4.3 Reconstruction parameters .3
4.4 Visualization .3
4.5 Analysis and interpretation of CT data .4
4.5.1 General .4
4.5.2 Feature testing/defect testing .4
4.5.3 Dimensional testing .4
5 Parameters and procedures for acceptable results . 6
5.1 Image quality parameters .6
5.1.1 Contrast .6
5.1.2 Noise .8
5.1.3 Signal to noise ratio .9
5.1.4 Contrast to noise ratio .10
5.1.5 Spatial resolution .10
5.2 Suitability of testing . 12
5.3 CT examination interpretation and acceptance criteria . 12
5.4 Records and reports . 13
5.5 Artefacts . 13
5.5.1 General . 13
5.5.2 Beam hardening artefacts . 13
5.5.3 Edge artefacts .14
5.5.4 Scattered radiation. 15
5.5.5 Instabilities . 15
5.5.6 Ring artefacts . 15
5.5.7 Centre of rotation error artefacts .16
5.5.8 Motion artefacts .17
5.5.9 Artefacts due to an insufficient number of projections .18
5.5.10 Cone beam artefacts . .18
Annex A (informative) Spatial resolution measurement using line pair gauges .20
Bibliography .23

iii
ISO 15708-3:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 135, Non-destructive testing, Subcommittee SC
5, Radiographic testing, in collaboration with the European Committee for Standardization (CEN) Technical
Committee CEN/TC 138, Non-destructive testing, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 15708-3:2017), which has been technically
revised.
The main changes are as follows:
— correction of Figure 5;
— correction and reordering of content in Clause 5;
— correction of definitions for N and N in Formula A.1;
C A
— correction of definition for σ in Formula A.2;
— editorial changes.
A list of all parts in the ISO 15708 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 15708-3:2025(en)
Non-destructive testing — Radiation methods for computed
tomography —
Part 3:
Operation and interpretation
1 Scope
This document provides an overview of the operation of a computed tomography (CT) system. This
document specifies steps for interpretation of CT results with the aim of providing the operator with
technical information to enable selection of suitable parameters.
This document is applicable to industrial imaging (i.e. non-medical applications) and specifies a consistent
set of definitions of CT performance parameters, including how these performance parameters relate to CT
system specifications.
This document is applicable to computed axial tomography.
This document does not apply to other types of tomography such as translational tomography and
tomosynthesis.
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.
ISO 15708-1, Non-destructive testing — Radiation methods for computed tomography — Part 1: Vocabulary
ISO 15708-2:2025, Non-destructive testing — Radiation methods for computed tomography — Part 2: Principle,
equipment and samples
ISO 15708-4:2025, Non-destructive testing — Radiation methods for computed tomography — Part 4:
Qualification
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 15708-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Operational procedure
4.1 General
For target-oriented computer tomography (CT) non-destructive testing inspection procedures, the test and
measurement tasks are defined in advance with regard to the size and type of features/defects to be verified,

ISO 15708-3:2025(en)
e.g. by specifying appropriate acceptance levels and geometry deviations. In the following, the process steps
of a CT application are described and information on its implementation is provided.
4.2 CT system set-up
4.2.1 General
The set-up of the CT system is based on the requirements for the respective task. The required spatial
resolution (taking into account the tube focal spot size), the contrast resolution, the voxel size and the
CT image quality can be derived from these requirements. The quality of the CT image is determined by
different parameters, which, under certain circumstances, counteract each other.
In the following, system parameters are described and information on setting up a CT system for non-
destructive testing inspection is provided. Due to the interactions between various system parameters, it
can be necessary to run through the set-up steps several times to acquire optimal data.
The optimum energy is the one that gives the best signal-to-noise ratio and not necessarily the one that gives
the clearest radiograph (the dependence of the detector efficiency on the energy shall be taken into account).
However, in order to differentiate between materials of different chemical composition, it can be necessary
to adjust the accelerating voltage to maximise the difference in their linear attenuation coefficients.
4.2.2 Geometry
The source-detector and source-object distances and thus also the beam angle used should be specified. To
achieve high spatial resolutions, the projection of the object onto the detector is magnified. The magnification
is equal to the ratio of the source-detector distance to the source-object distance. An increasing source-
detector distance leads to a reduced radiation intensity at the detector and therefore to a reduced signal to
noise ratio. Accordingly, this also applies when using detectors with improved detector resolution, which
results in a reduction of the signal-to-noise ratio due to the reduced radiation dose per pixel. For this reason,
it is generally preferable to minimise the source-object distance.
To obtain high radiation intensity at the detector, the source-detector distance should be selected as small
as possible taking into account the required spatial resolution, so that the beam cone still fully illuminates
the detector. In the case of 3D-CT, the (in general vertical) total cone beam angle measured perpendicular
to the rotation axis should typically be less than 11° in order to minimise such reconstruction-determined
[2]
distortions of the 3D model (“Feldkamp” algorithm ). In addition, these restrictions do not apply for the
perpendicular (in general horizontal) beam angle. At a higher geometric magnification, the object shall be
positioned as near as possible to the source, taking into consideration the limit of sharpness due to the size
of the focal spot of the X-ray source. The object shall be rotated by at least 180° plus the beam angle of the
X-ray beam, whereby the data quality is improved by an increased rotational angle. For this reason, the
object is typically rotated by 360°. Ideally, the number of angular increments should be at least π/2 × matrix
size (odd number of projections per 360°), where the matrix size is the number of voxels across the sample
diameter or its largest dimension. For more information, see 5.5.
The number of projections should be > (π × matrix size) for best reconstruction quality (number of
projections per 360°).
In order to obtain information about the specimen that is as complete as possible, the object (or the
interesting section of the object) shall be completely mapped on the detector in each projection. For large
components that exceed the beam cone, a so-called measurement range extension is used. This extension
of the measuring range is achieved by laterally displacing either the object or the detector, recording the
projection data in sequential measurements, and finally, concatenating (joining) them. Under certain
circumstances, it is also possible to scan only a part of the object (region-of-interest CT), which leads to
limited data quality in the form of so-called truncations.
A possible deviation of the recording geometry (offset between the projected axis of rotation and the centre
line of the projection image) shall be corrected to obtain the most accurate reconstruction as possible. This
shall be achieved by carefully aligning the system or by software correction.

ISO 15708-3:2025(en)
4.2.3 X-ray source
At the X-ray source, the maximum beam energy and the tube current shall be set such that sufficient
penetration of the test object and the maximum tube power with a sufficiently small focal spot are ensured.
The required voltage shall be determined by the maximum path length in the material to be X-rayed in
accordance with ISO 15708-2:2025, 8.2. For optimum conditions of the measurement results, an attenuation
ratio of less or equal to 1:10 should be used. This means, that the grey value after the sample should be
about 10 % of the free beam value. The optimal range can be achieved by using pre-filters at the tube port.
It should be noted that each pre-filter reduces the intensity. Pre-filters have the additional advantage of
beam hardening, which reduces the beam hardening artifacts after reconstruction, although further
improvements can be made through software corrections.
4.2.4 Detector
The following detector settings need to be set appropriately for the sample to be scanned:
— exposure time (frame rate);
— number of integrations/averagings per projection;
— digitisation, gain and offset;
— Skip projections
— binning.
If necessary, corrections for offset, gain and bad pixels (which may depend on X-ray settings) should be
applied.
The individual CT projection is determined by the geometric resolution, the sensitivity, the dynamics and
the noise of the detector. The gain and exposure time can be adjusted together depending on the radiation
intensity of the source so that the maximum digitised intensity in the free beam does not exceed 90 % of the
saturation level.
To reduce scattered radiation, a thin filter, grid, or lamellae can be used directly in front of the detector
(intermediate filtering).
The ideal acquisition time is dependent on the required quality of the CT data and is often limited by the
time available for testing.
4.3 Reconstruction parameters
The volumetric region to be reconstructed, the size of the CT volume (in terms of voxels) and its dynamic
range (which should take into account the dynamic range of the detector) shall be specified. To achieve
sufficient CT image quality, the settings for the reconstruction algorithm or corrections should be optimised.
The volumetric region is defined by the number of voxels along the X, Y and Z axes.
4.4 Visualization
Using volume visualisation, the reconstructed CT data image can be presented as a 3D object. Individual
grey values can be assigned any colour and opacity values to highlight or hide materials with different
X-ray densities. Zooming, scrolling, setting contrast, brightness, colour and lighting facilitate an optimal
presentation of the CT volume. In addition, it is possible to place user-defined sectional planes through the
object to examine the internal structure, or to visualise the CT volume interactively, for example by rotating
and moving it as a 3D object. Image processing can be applied to CT data to improve feature detection.
There is a possibility that the whole CT volume cannot be loaded at full resolution into memory at once.
Consequently, the CT volume can be split into different smaller parts of the total volume for separate viewing.

ISO 15708-3:2025(en)
4.5 Analysis and interpretation of CT data
4.5.1 General
Typical internal features for inspection are pores, cavities, cracks, inclusions, impurities or inhomogeneous
material distributions.
Typical measurement tasks are obtaining dimensional properties (such as length or wall thickness) or
calculating object morphology.
4.5.2 Feature testing/defect testing
Features in the sample generally lead to changes in the CT grey value in the CT data. The analysis of CT data
is performed by qualified personnel using software. A suitable contrast range or an automatic or manual
calibration is used. The location, the CT grey value and the dimensions of features can be determined. Several
tools are available for this purpose, including manual or automatic tools such as strobe lines or gauges that
engage at grey value thresholds or edges. To examine the structure and location of assembled components, a
qualitative comparison of CT volumes without determination of the dimensions can be sufficient.
For automatic determination using visualisation software tools (e.g. for defect analysis), a calibration via
specification of a grey value range is, in general, required for the sample material to be measured. The grey
values can be specified manually using histograms or in an interactive manner.
The detectability of features depends on the size of the feature relative to the geometric resolution and the
contrast resolution compared with the contrast difference of the feature to the base material, as well as the
quality of the image (signal to noise ratio, etc.) and any possible interference effects between adjacent voxels
(partial volume effect). For the detectability of singular pores, cavities or cracks, their minimum extent
should typically be 2 to 3 times the demagnified pixel size of the detector (at the position of the sample).
4.5.3 Dimensional testing
4.5.3.1 General
Depending on the task at hand, various methods are currently used to determine geometric features. Point-
to-point distances can be determined manually in the CT slices, or more complex features can be extracted
with the help of analysis software.
The measurement of the geometric properties of an object using CT is an indirect method, in which the
dimensional measurement takes place in or is derived from CT data. For this reason, in order to facilitate
precise measurements, an accurate knowledge of two important variables is necessary:
— the precise image scale or voxel size;
— the boundary surface of two materials, for example the component surface (material-to-air transition),
which can be determined via a CT grey value threshold in the CT volume.
4.5.3.2 Determination of precise image scale
The precise image scale or voxel size shall be determined by measuring a suitable calibration standard
(together with the measurement object and directly before/after testing of the object inspection) or by
using a reference geometry on the object. For this purpose, the voxel size or magnification M, specified by
the CT system is compared with the actual available and precisely determined (using the reference body/
geometry) voxel size or magnification. Thus, for example, the exact voxel size can be determined with high
precision via measurements without the disturbing influence of other variables, e.g. the precise position
of the component surface (grey value threshold) in the CT volume, for the centre distances of a test piece
(e.g. dumbbell, see Figure 1). In this procedure the CT grey values of the test item can be influenced by the
accompanying reference bodies (e.g. due to changes in the contrast ratios, interferences and artefacts).
Based on the actual voxel sizes determined in this way, the visualisation software can be scaled/corrected
accordingly to the voxel size specified by the system.

ISO 15708-3:2025(en)
Figure 1 — Reference objects (dumbbells of different sizes)
4.5.3.3 Threshold value determination
For dimensional measurements, the component surface or material contact surface shall be determined in
the CT volume. The component surface usually results from the transition from solid object to surrounding
air. The boundary surface is defined via a threshold value and is thus dependent on the materials and the
X-ray settings. This threshold can be specified globally for the entire CT volume as an average grey value of
e.g. the material and air. This is sometimes known as the “ISO50 threshold” (from the Greek, “isos” means
“equal”). A global threshold value or calibration using the ISO50 threshold is suitable for many measurement
tasks on objects made from homogeneous materials.
A global threshold is not suitable for objects made of different materials. In these cases, different
thresholds shall be used according to the materials either side of the boundary. Even with objects made
from homogeneous materials, beam hardening, scattering and other artefacts can result in local dimming
or lightening in the CT volume, which would distort the measurement results. The grey value threshold,
e.g. for surfaces inside the component, therefore often differs from that for surfaces on the outside of the
component. If necessary, the threshold can be determined locally from the grey levels on both sides of the
boundary. A determination of the overall component surface via locally determined threshold values is more
tole
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