1、BS ISO 15708-3:2017Non-destructive testing Radiation methods forcomputed tomographyPart 3: Operation and interpretationBSI Standards PublicationWB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06BS ISO 15708-3:2017 BRITISH STANDARDNational forewordThis British Standard is the UK implementation
2、of ISO 15708-3:2017.The UK participation in its preparation was entrusted to Technical Committee WEE/46, Non-destructive testing.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions
3、 of a contract. Users are responsible for its correct application. The British Standards Institution 2017.Published by BSI Standards Limited 2017ISBN 978 0 580 95776 5 ICS 19.100 Compliance with a British Standard cannot confer immunity from legal obligations.This British Standard was published unde
4、r the authority of the Standards Policy and Strategy Committee on 31 March 2017.Amendments/corrigenda issued since publicationDate T e x t a f f e c t e dBS ISO 15708-3:2017 ISO 2017Non-destructive testing Radiation methods for computed tomography Part 3: Operation and interpretationEssais non destr
5、uctifs Mthodes par rayonnements pour la tomographie informatise Partie 3: Fonctionnement et interprtationINTERNATIONAL STANDARDISO15708-3First edition2017-02Reference numberISO 15708-3:2017(E)BS ISO 15708-3:2017ISO 15708-3:2017(E)ii ISO 2017 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2017,
6、Published in SwitzerlandAll rights reserved. Unless otherwise specified, 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. Per
7、mission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 15708-3:2017ISO 15708-3:2017(
8、E)Foreword iv1 Scope . 12 Normative references 13 Terms and definitions . 14 Operational procedure . 14.1 General . 14.2 CT system set-up . 24.2.1 General 24.2.2 Geometry 24.2.3 X-ray source 34.2.4 Detector . 34.3 Reconstruction parameters . 34.4 Visualization 34.5 Analysis and interpretation of CT
9、images 44.5.1 General 44.5.2 Feature testing/defect testing 44.5.3 Dimensional testing 45 Requirements for acceptable results 75.1 Image quality parameters . 75.1.1 Contrast . 75.1.2 Noise . 85.1.3 Signal to noise ratio . 95.1.4 Contrast to noise ratio . 95.1.5 Spatial resolution .105.2 Suitability
10、of testing . 125.3 CT examination interpretation and acceptance criteria 125.4 Records and reports 125.5 Artefacts . 135.5.1 General. 135.5.2 Beam hardening artefacts . 135.5.3 Edge artefacts 145.5.4 Scattered radiation 155.5.5 Instabilities 155.5.6 Ring artefacts . 155.5.7 Centre of rotation error
11、artefacts .165.5.8 Motion artefacts .175.5.9 Artefacts due to an insufficient number of projections .185.5.10 Cone beam artefacts .18Annex A (informative) Spatial resolution measurement using line pair gauges .19Bibliography .23 ISO 2017 All rights reserved iiiContents PageBS ISO 15708-3:2017ISO 157
12、08-3:2017(E)ForewordISO (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 fo
13、r 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
14、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 documents should be noted.
15、This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying a
16、ny or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents).Any trade name used in this document is information given for the convenience o
17、f users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the follo
18、wing URL: www .iso .org/ iso/ foreword .htmlThis document was prepared by the European Committee for Standardization (CEN) (as EN 16016-3) and was adopted, under a special “fast-track procedure”, by Technical Committee ISO/TC 135, Non-destructive testing, Subcommittee SC 5, Radiographic testing, in
19、parallel with its approval by the ISO member bodies. This first edition of ISO 15708-3 cancels and replaces ISO 15708-2:2002, of which it forms the subject of a technical revision. It takes into consideration developments in computed tomography (CT) and computational power over the preceding decade.
20、A list of all parts in the ISO 15708 series can be found on the ISO website.iv ISO 2017 All rights reservedBS ISO 15708-3:2017INTERNATIONAL STANDARD ISO 15708-3:2017(E)Non-destructive testing Radiation methods for computed tomography Part 3: Operation and interpretation1 ScopeThis document presents
21、an outline of the operation of a computed tomography (CT) system and the interpretation of results with the aim of providing the operator with technical information to enable the selection of suitable parameters. It is applicable to industrial imaging (i.e. non-medical applications) and gives a cons
22、istent set of CT performance parameter definitions, including how those performance parameters relate to CT system specifications. This document deals with computed axial tomography and excludes other types of tomography such as translational tomography and tomosynthesis.2 Normative referencesThe fo
23、llowing 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
24、15708-1:2017, Non-destructive testing Radiation methods for computed tomography Part 1: TerminologyISO 15708-2:2017, Non-destructive testing Radiation methods for computed tomography Part 2: Principle, equipment and samples3 Terms and definitionsFor the purposes of this document, the terms and defin
25、itions given in ISO 15708-1 apply.ISO and IEC maintain terminological databases for use in standardization at the following addresses: IEC Electropedia: available at h t t p :/ www .electropedia .org/ ISO Online browsing platform: available at h t t p :/ www .iso .org/ obp4 Operational procedure4.1
26、GeneralFor target-oriented computer tomography (CT) inspection procedures, the test and measurement tasks are defined in advance with regard to the size and type of features/defects to be verified; for example, through the specification of appropriate acceptance levels and geometry deviations. In th
27、e following, the process steps of a CT application are described and information on its implementation provided. ISO 2017 All rights reserved 1BS ISO 15708-3:2017ISO 15708-3:2017(E)4.2 CT system set-up4.2.1 GeneralThe CT system set-up is oriented towards the requirements for the given task. The requ
28、ired spatial resolution (taking into account the tube focal spot size), contrast resolution, 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 f
29、ollowing, system parameters are described and information is provided on setting up a CT system for inspection. Due to the interactions of the different system parameters, it may be necessary to run through the set-up steps several times in order to acquire optimal data.The optimal energy is that wh
30、ich gives the best signal-to-noise ratio and not necessarily that which gives the clearest radiograph (the dependency of the detector efficiency on the energy is to be taken into account). However, in order to differentiate between materials of different chemical composition it may be necessary to a
31、djust the accelerating voltage to maximise the difference in their linear attenuation coefficients.4.2.2 GeometryThe source-detector and source-object distances and thus also the beam angle used should be specified. In order to achieve high resolutions, the projection can be magnified onto the detec
32、tor. The magnification is equal to the ratio of the source-detector distance to the source-object distance. Increasing source-detector distance leads to a reduced intensity at the detector and thus to a reduced signal to noise ratio. Accordingly, this also applies when using detectors with improved
33、detector resolution, which can result in a reduction of the signal-to-noise ratio due to the reduced intensity per pixel. In general, for this reason, minimisation of the source-object distance is to be preferred.In order to obtain high beam intensity at the detector, the source-detector distance sh
34、ould be selected so that it is as small as possible taking into account the required 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 parallel to the rotation axis should typically be less than 15, b
35、ut this is specimen dependant, in order to minimise reconstruction-determined (Feldkamp) distortions of the 3D model. In addition, these restrictions do not apply for the perpendicular (in general horizontal) beam angle. For a higher geometric magnification, the object must be positioned as near as
36、possible to the source, taking into consideration the limit on sharpness imposed by focal spot size. The rotation of the object must take place at at least 180 plus beam angle of the X-ray beam, whereby an improved data quality is the result of an increasing number of angular increments. For this re
37、ason, the object is typically turned through 360 . Ideally, the number of angular increments should be at least /2 matrix size (uneven number of projections per 360) where the matrix size is the number of voxels across the sample diameter or the largest dimension. For more information, refer to 5.5.
38、The number of projections should be matrix size for best reconstruction quality (even or uneven number of projections per 360).In order to obtain as complete information as possible on the specimen, the requirement in general for a CT is that the object (or the interesting section of the object) is
39、completely mapped in each projection on the detector. For large components that exceed the beam cone, a so-called measurement range extension is used. This measurement range extension is accomplished by laterally displacing either the object or the detector, recording the projection data in sequenti
40、al measurements, and finally concatenating (joining) them. Under certain circumstances, it is also possible to only scan a part of the object (region-of-interest CT), which may lead to a restricted data quality in the form of so-called truncations.A possible deviation of the recording geometry (offs
41、et between the projected axis of rotation and the centre line of the image) must be corrected for in order to obtain a reconstruction which is as precise as possible. This can be achieved by careful realignment of the system or be corrected using software.2 ISO 2017 All rights reservedBS ISO 15708-3
42、2017ISO 15708-3:2017(E)4.2.3 X-ray sourceAt the X-ray source, the maximum beam energy and tube current are to be set such that sufficient penetration of the test object and tube power with a sufficiently small focal spot are ensured. The required voltage shall be determined by the maximum path leng
43、th in the material to be X-rayed in accordance with ISO 15708-2:2017, 8.2. For the best measurement results, an attenuation ratio of approx. 1:10 should be used. That is the grey level through the sample should be about 10 % of the white level (both measured with respect to the dark level). The opti
44、mal range can be achieved through the use of pre-filters. It should be noted that every pre-filter reduces the intensity. Pre-filters have the additional advantage of reducing beam hardening, though further improvements can be made with software correction.4.2.4 DetectorThe following detector settin
45、gs need to be set appropriately for the sample being scanned: exposure time (frame rate); number of integrations per projection; digitisation gain and offset; binning.If necessary, corrections for offset, gain and bad pixels (which may depend on X-ray settings) should be applied.The individual CT pr
46、ojection is determined by the detector properties: its geometric resolution, its sensitivity, dynamics and noise. The gain and exposure time can be adjusted together with the radiation intensity of the source so that the maximum digitised intensity does not exceed 90 % of the saturation level.To red
47、uce 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 image and it is often limited by the time available for inspection.4.3 Reconstruction parametersTh
48、e volumetric region to be reconstructed, the size of the CT image (in terms of voxels) as well as its dynamic range (which should take into account the detector dynamic range) shall be specified. In order to achieve sufficient CT image quality, settings for the reconstruction algorithm or correction
49、s should be optimised.The volumetric region is defined by the number of voxels along the X, Y and Z axes.4.4 VisualizationUsing volume visualisation, the CT 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 image. In addition, it is possible to place user-defined sectional planes through the o
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