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1、 Reference number ISO 15708-1:2002(E) ISO 2002 INTERNATIONAL STANDARD ISO 15708-1 First edition 2002-06-01 Non-destructive testing Radiation methods Computed tomography Part 1: Principles Essais non destructifs Moyens utilisant les rayonnements Tomographie informatise Partie 1: Principes Copyright I
2、nternational Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/04/2007 23:10:03 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15708-1:2002(E) PDF disclaimer This PDF file may
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6、therwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyr
7、ight office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.ch Web www.iso.ch Printed in Switzerland ii ISO 2002 All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employe
8、es/1111111001, User=Wing, Bernie Not for Resale, 04/04/2007 23:10:03 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15708-1:2002(E) ISO 2002 All rights reserved iii Contents Page Foreword.iv Introduction.v 1 Scope1 2 Pre-amble .1 3 Abbreviations.1 4 Requirements.2 5 Ap
9、paratus.8 6 Theoretical background13 7 Interpretation of results 23 8 Precision and bias.39 Annex A (normative) Glossary of terms 41 Bibliography60 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not
10、 for Resale, 04/04/2007 23:10:03 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15708-1:2002(E) iv ISO 2002 All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies).
11、 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-
12、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. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part
13、3. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a
14、 vote. Attention is drawn to the possibility that some of the elements of this part of ISO 15708 may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 15708-1 was prepared by Technical Committee ISO/TC 135, Non-destructive testing,
15、Subcommittee SC 5, Radiation methods. ISO 15708 consists of the following parts, under the general title Non-destructive testing Radiation methods Computed tomography: Part 1: Principles Part 2: Examination practices Annex A forms a normative part of this part of ISO 15708. Copyright International O
16、rganization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/04/2007 23:10:03 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15708-1:2002(E) ISO 2002 All rights reserved v Introduction Th
17、is part of ISO 15708 provides a tutorial introduction to the theory and use of computed tomography. It begins with an overview intended for the interested reader possessing a general technical background. Subsequent, more technical clauses describe the physical and mathematical basis of CT technolog
18、y, the hardware and software requirements of CT equipment, and the fundamental measures of CT performance. This part of ISO 15708 includes an extensive glossary (with discussions) of CT terminology and an extensive list of references to more technical publications on the subject. Most importantly, t
19、his part of ISO 15708 establishes consensus definitions for basic measures of CT performance, enabling purchasers and suppliers of CT systems and services to communicate unambiguously with reference to a recognized standard. It also provides a few carefully selected equations relating measures of CT
20、 performance to key system parameters. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/04/2007 23:10:03 MDTNo reproduction or networking permitted without license from IHS -,-,- Co
21、pyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/04/2007 23:10:03 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISO 15708-1:2002(E)
22、ISO 2002 All rights reserved 1 Non-destructive testing Radiation methods Computed tomography Part 1: Principles 1 Scope This part of ISO 15708 gives guidelines for, and defines terms for addressing the general principles of X-ray CT as they apply to industrial imaging. It also gives guidelines for a
23、 consistent set of CT performance parameter definitions, including how these performance parameters relate to CT system specifications. 2 Pre-amble CT, being a radiographic modality, uses much the same vocabulary as other X-ray techniques. Because a number of terms have meanings or carry implication
24、s unique to CT, they appear with explanations in annex A. Throughout this part of ISO 15708, the term “X-ray” is used to denote penetrating electromagnetic radiation, however, electromagnetic radiation may be either X-rays or gamma rays. 3 Abbreviations BW beam width CDD contrast-detail-dose CT comp
25、uted tomography CAT computerized axial tomography DR digital radiography ERF edge response function LSF line spread function MTF modulation transfer function NDE non-destructive evaluation PDF probability distribution function PSF point spread function Copyright International Organization for Standa
26、rdization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/04/2007 23:10:03 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15708-1:2002(E) 2 ISO 2002 All rights reserved 4 Requirements 4.1 Summary of compute
27、d tomography Computed tomography (CT) is a radiographic method that provides an ideal examination technique whenever the primary goal is to locate and size planar and volumetric detail in three dimensions. Because of the relatively good penetrability of X-rays, as well as the sensitivity of absorpti
28、on cross sections to atomic chemistry, CT permits the non-destructive physical and, to a limited extent, chemical characterization of the internal structure of materials. Also, since the method is X-ray based, it applies equally well to metallic and non-metallic specimens, solid and fibrous material
29、s, and smooth and irregularly surfaced objects. When used in conjunction with other non- destructive evaluation (NDE) methods, such as ultrasound, CT data can provide evaluations of material integrity that cannot currently be provided non-destructively by any other means. This part of ISO 15708 is i
30、ntended to satisfy two general needs for users of industrial CT equipment: a) the need for a tutorial document addressing the general principles of X-ray CT as they apply to industrial imaging; b) the need for a consistent set of CT performance parameter definitions, including how these performance
31、parameters relate to CT system specifications. Potential users and buyers, as well as experienced CT inspectors, will find this part of ISO 15708 a useful source of information for determining the suitability of CT for particular examination problems, for predicting CT system performance in new situ
32、ations and for developing and prescribing new scan procedures. This part of ISO 15708 does not specify test objects and test procedures for comparing the relative performance of different CT systems; nor does it treat CT inspection techniques, such as the best selection of scan parameters, the prefe
33、rred implementation of scan procedures, the analysis of image data to extract densitometric information or the establishment of accept/reject criteria for a new object. Standard practices and methods are not within the purview of this part of ISO 15708. The reader is advised, however, that examinati
34、on practices are generally part- and application-specific, and industrial CT usage is new enough that in many instances a consensus has not yet emerged. The situation is complicated further by the fact that CT system hardware and performance capabilities are still undergoing significant evolution an
35、d improvement. Consequently, an attempt to address generic examination procedures is eschewed in favour of providing a thorough treatment of the principles by which examination methods can be developed or existing ones revised. The principal advantage of CT is that it non-destructively provides quan
36、titative densitometric (i.e., density and geometry) images of thin cross sections through an object. Because of the absence of structural noise from detail outside the thin plane of inspection, images are much easier to interpret than with conventional radiographic data. The new user can learn quick
37、ly (often upon first exposure to the technology) to read CT data because the images correspond more closely to the way the human mind visualizes three-dimensional structures than conventional projection radiography. Further, because CT images are digital, they may be enhanced, analysed, compressed,
38、archived, input as data into performance calculations, compared with digital data from other NDE modalities, or transmitted to other locations for remote viewing. Additionally, CT images exhibit enhanced contrast discrimination over compact areas. This capability has no classical analogue. Contrast
39、discrimination of better than 0,1 % at three-sigma confidence levels over areas as small as one-fifth of one percent the size of the object of interest are common. With proper calibration, dimensional inspections and absolute density determinations can also be made very accurately. Dimensionally, vi
40、rtually all CT systems provide a pixel resolution of roughly 1 part in 1 000, and metrological algorithms, using a priori knowledge, can often measure dimensions to one-tenth of one pixel or so with three-sigma accuracies. Attenuation values can also be related accurately to material densities. If d
41、etails in the image are known to be pure homogeneous elements, the density values may still be sufficient to identify materials in some cases. For the case in which no a priori information is available, CT densities cannot be used to identify unknown materials unambiguously, since an infinite spectr
42、um of compounds can be envisioned that will yield any given observed attenuation. In this instance, the exceptional density sensitivity of CT can still be used to determine part morphology and highlight structural irregularities. Copyright International Organization for Standardization Provided by I
43、HS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/04/2007 23:10:03 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15708-1:2002(E) ISO 2002 All rights reserved 3 In some cases, dual energy (DE) CT scans can help identify u
44、nknown components. DE scans provide accurate electron density and atomic number images, providing better characterizations of the materials. In the case of known materials, the additional information can be traded for improved conspicuousness, faster scans or improved characterization. In the case o
45、f unknown materials, the additional information often allows educated guesses to be made as to the probable composition of an object. CT, as a digital technique with data convertible to other formats, has proven valuable in the industrial application areas of rapid prototyping, reverse engineering a
46、nd metrology. Rapid prototyping can be accomplished utilizing a class of manufacturing techniques where parts are built from computer models in a variety of materials. Stereolithography is one such technique that can utilize the thin slice information of CT to produce accurate polymer parts. Taking
47、multiple CT slices, the two-dimensional images can be assembled to produce complete three-dimensional representations of scanned components. The data are presented to the stereolithography system as full volume information or simply contour plots, allowing the generation of either filled or hollow p
48、olymer parts. The choice of data would be based on the rapid tooling techniques that are applied in the specific application area. CT-assisted reverse engineering methods are successful in enabling older designs without computer-aided design (CAD) files to access the many available rapid tooling techniques currently available. In reverse engineering applications, as in rapid prototyping, the two-dimensional images can be assembled to produce complete thr