1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS EN 16016-2:2011Non destructive testing Radiation methods Computed tomographyPart 2: Principle, equipment and samplesBS EN 16016-2:2011 BRITISH STANDARDNational forewordThis Br
2、itish Standard is the UK implementation of EN 16016-2:2011.The UK participation in its preparation was entrusted to TechnicalCommittee WEE/46, Non-destructive testing.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to
3、 include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 62739 2ICS 19.100Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy
4、 and Strategy Committee on 30 September 2011.Amendments issued since publicationDate Text affectedBS EN 16016-2:2011EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 16016-2 August 2011 ICS 19.100 English Version Non destructive testing - Radiation methods - Computed tomography - Part 2: Principl
5、e, equipment and samples Essais non destructifs - Mthodes par rayonnements - Tomographie numrise - Partie 2 : Principes, quipementset chantillons Zerstrungsfreie Prfung - Durchstrahlungsverfahren - Computertomographie - Teil 2: Grundlagen, Gerte und Proben This European Standard was approved by CEN
6、on 29 July 2011. 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
7、 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 t
8、o the CEN-CENELEC Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Lux
9、embourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2011 CEN All ri
10、ghts of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 16016-2:2011: EBS EN 16016-2:2011EN 16016-2:2011 (E) 2 Contents Page Foreword 3Introduction .41 Scope 52 Normative references 53 Terms and definitions .54 General principles54.1 Basic principle
11、s .54.2 Advantages of CT 54.3 Limitations of CT64.4 Main CT process steps 64.4.1 Acquisition .64.4.2 Reconstruction .74.4.3 Visualisation and analysis 74.5 Artefacts in CT images 85 Equipment and apparatus .85.1 General 85.2 Radiation sources 95.3 Detectors . 105.4 Manipulation 105.5 Acquisition, re
12、construction, visualisation and storage system 106 CT system stability . 116.1 General . 116.2 X-Ray Stability . 116.3 Manipulator stability . 117 Geometric alignment 128 Sample considerations 128.1 Size and shape of sample 128.2 Materials (including table voltage / thickness of penetration) . 12Ann
13、ex A (informative) CT system components 15A.1 Radiation sources . 15A.1.1 Open Tube X-ray sets . 15A.1.2 Sealed Tube X-ray Sets 16A.1.3 Linear Accelerators 16A.1.4 X-ray target assemblies . 17A.2 Detectors . 18A.2.1 Ionisation detectors 18A.2.2 Scintillation detectors 18A.2.3 Semiconductor detectors
14、 19A.3 Manipulation 19A.4 Acquisition, reconstruction, visualisation and storage system 19A.4.1 Acquisition system . 19A.4.2 Reconstruction system 20A.4.3 Visualisation system 20A.4.4 Storage system . 20Bibliography . 21BS EN 16016-2:2011EN 16016-2:2011 (E) 3 Foreword This document (EN 16016-2:2011)
15、 has been prepared by 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 February 2012, and confli
16、cting national standards shall be withdrawn at the latest by February 2012. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. EN 16016 c
17、onsists of the following parts: Non destructive testing Radiation methods Computed tomography Part 1: Terminology; Non destructive testing Radiation methods Computed tomography Part 2: Principle, equipment and samples; Non destructive testing Radiation methods Computed tomography Part 3: Operation a
18、nd interpretation; Non destructive testing Radiation methods Computed tomography Part 4: Qualification. 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, Croati
19、a, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. BS EN 16016-2:2011EN 16016-2:2
20、011 (E) 4 Introduction This document gives guidelines for the general principles of X-ray computed tomography (CT) applicable to industrial imaging (in the context of this standard, industrial means non-medical applications); it also gives a consistent set of CT performance parameter definitions, in
21、cluding how these 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. BS EN 16016-2:2011EN 16016-2:2011 (E) 5 1 Scope This European Standard specifies
22、the general principles of computed tomography (CT), the equipment used and basic considerations of sample, materials and geometry. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. F
23、or undated references, the latest edition of the referenced document (including any amendments) applies. EN 473, Non-destructive testing Qualification and certification of NDT personnel General principles EN 16016-1:2011, Non destructive testing Radiation method Computed tomography Part 1: Terminolo
24、gy EN 16016-3:2011, Non destructive testing Radiation methods Part 3: Operation and interpretation EN 16016-4:2011, Non destructive testing Radiation methods Part 4: Qualification 3 Terms and definitions For the purposes of this document, the terms and definitions given in EN 16016-1:2011 apply. 4 G
25、eneral principles 4.1 Basic principles Computed tomography is a radiographic inspection method which delivers three-dimensional information of an object from a number of radiographic projections either over cross-sectional planes (CT slices) or over the complete volume. Radiographic imaging is possi
26、ble because different materials have different X-ray attenuation coefficients. In CT images, the X-ray linear attenuation coefficients are represented as different CT grey values (or in false colour). For conventional radiography the three-dimensional object is X-rayed from one direction and an X-ra
27、y projection is produced with the corresponding information aggregated over the ray path. In contrast, multiple X-ray-projections of an object are acquired at different projection angles during a CT scan. From these projection images the actual slices or volume are reconstructed. The fundamental adv
28、antage compared to radiography is the preservation of full volumetric information. The resulting CT image (2D CT slice or 3D CT volume), is a quantitative representation of the X-ray linear attenuation coefficient averaged over the finite volume of the corresponding volume element (voxel) at each po
29、sition in the sample. The linear attenuation coefficient characterizes the local instantaneous rate at which X-rays are attenuated as they propagate through the object during the scan. The attenuation of the X-rays as they interact with matter is the result of several different interaction mechanism
30、s: Compton scattering and photoelectric absorption being the predominant ones for X-ray CT. The linear attenuation coefficient depends on the atomic numbers of the corresponding materials and is proportional to the material density. It also depends on the energy of the X-ray beam. 4.2 Advantages of
31、CT Computed tomography (CT) is a radiographic method that can be an excellent examination technique whenever the primary goal is to locate and quantify volumetric details in three dimensions. In addition, since BS EN 16016-2:2011EN 16016-2:2011 (E) 6 the method is X-ray based it can be used on metal
32、lic and non-metallic samples, solid and fibrous materials and smooth and irregularly surfaced objects. In contrast to conventional radiography, where the internal features of a sample are projected onto a single image plane and thus are superposed on each other, in CT images the individual features
33、of the sample appear separate from each other, preserving the full spatial information. With proper calibration, dimensional inspections and material density determinations can also be made. Complete three-dimensional representations of examined objects can be obtained either by reconstructing and a
34、ssembling successive CT slices (2D-CT) or by direct 3D CT image (3D-CT) reconstruction. Computed tomography is thus valuable in the industrial application areas of non-destructive testing, 2D and 3D metrology and reverse engineering. CT has several advantages over conventional metrology methods: acq
35、uisition without contact; access to internal and external dimensional information; a direct input to 3D modelling especially of internal structures. In some cases, dual energy (DE) CT acquisitions can help to obtain information on the material density and the average atomic number of certain materia
36、ls. In the case of known materials the additional information can be traded for improved discrimination or improved characterization. 4.3 Limitations of CT CT is an indirect test procedure and measurements (e.g. of the size of material faults; of wall thicknesses must be compared with another absolu
37、te measurement procedure, see EN 16016-3). Another potential drawback of CT imaging is the possible occurrence of artefacts (see 4.5) in the data. Artefacts limit the ability to quantitatively extract information from an image. Therefore, as with any examination technique, the user must be able to r
38、ecognize and discount common artefacts subjectively. Like any imaging system, a CT system can never reproduce an exact image of the scanned object. The accuracy of the CT image is dictated largely by the competing influences of the imaging system, namely spatial resolution, statistical noise and art
39、efacts. Each of these aspects is discussed briefly in 4.4.1. A more complete description will be found in EN 16016-3. CT grey values cannot be used to identify unknown materials unambiguously unless a priori information is available, since a given experimental value measured at a given position may
40、correspond to a broad range of materials. Another important consideration is to have sufficient X-ray transmission through the sample at all projection angles (see 8.2) without saturating any part of the detector. 4.4 Main CT process steps 4.4.1 Acquisition During a CT scan, multiple projections are
41、 taken in a systematic way: the images are acquired from a number of different viewing angles. Feature recognition depends, among other factors, on the number of angles from which the individual projections are taken. The CT image quality can be improved if the number of projections of a scan is inc
42、reased. As all image capture systems contain inherent artefacts, CT scans usually begin with the capture of offset and gain reference images to allow flat field correction; using black (X-rays off) and white (X-rays on with the sample out of the field of view) images to correct for detector anomalie
43、s. The capture of reference images for BS EN 16016-2:2011EN 16016-2:2011 (E) 7 distortion correction (pin cushion distortion in the case of camera-based detector systems with optical distortion), and centre of rotation correction can also take place at this stage. Each subsequent captured image for
44、the CT data set has these corrections applied to it. Some systems can be configured to either the X-ray settings or enhance the image to ensure that the background intensity level of the captured images remains constant throughout the duration of the CT scan. The quality of a CT image depends on a n
45、umber of system-level performance factors, with one of the most important being spatial resolution. Spatial resolution is generally quantified in terms of the smallest separation at which two features can be distinguished as separate entities. The limits of spatial resolution are determined by the d
46、esign and construction of the system and by the resolution of and number of CT projections. The resolution of the CT projection is limited by the maximum magnification that can be used while still imaging all parts of the sample at all rotation angles. It is important to notice that the smallest fea
47、ture that can be detected in a CT image is not the same as the smallest that can be resolved spatially. A feature considerably smaller than a single voxel can affect the voxel to which it corresponds to such an extent that it appears with a visible contrast so that it can be easily detected with res
48、pect to adjacent voxels. This phenomenon is due to the “partial-volume effect”. Although region-of-interest CT (local tomography) can improve spatial resolution in specified regions of larger objects, it introduces artefacts (due to incomplete data) which can sometimes be reduced with special proces
49、sing. Radiographic imaging as used for CT examination is always affected by noise. In radiography this noise arises from two sources: (1) intrinsic variation corresponding to photon statistics related to the emission and detection of photons and (2) variations specific to instruments and processing used. Noise in CT projections is often amplified b
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