1、Medical electrical equipment Exposure index of digital X-rayimaging systems Part 1: Definitions and requirements for general radiographyBS EN 62494-1:2008raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI British StandardsNational forewordThis Britis
2、h Standard is the UK implementation of EN 62494-1:2008. It isidentical to IEC 62494-1:2008.The UK participation in its preparation was entrusted by Technical CommitteeCH/62, Electromedical equipment in medical practice, to SubcommitteeCH/62/2, Diagnostic imaging equipment.A list of organizations rep
3、resented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisions of acontract. Users are responsible for its correct application. BSI 2008ISBN 978 0 580 57718 5ICS 11.040.50BRITISH STANDARDBS EN 62494-1:2008Compliance wit
4、h a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of the StandardsPolicy and Strategy Committee on 31 March 2009 Amendments issued since publicationAmd. No. Date Text affectedEUROPEAN STANDARD EN 62494-1 NORME EUROPENNE EUROPISC
5、HE NORM November 2008 CENELEC European Committee for Electrotechnical Standardization Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B - 1050 Brussels 2008 CENELEC - All rights of exploitation in any form and
6、by any means reserved worldwide for CENELEC members. Ref. No. EN 62494-1:2008 E ICS 11.040.50 English version Medical electrical equipment - Exposure index of digital X-ray imaging systems - Part 1: Definitions and requirements for general radiography (IEC 62494-1:2008) Appareils lectromdicaux - Ind
7、ice dexposition des systmes dimagerie numrique rayonnement X - Partie 1: Dfinitions et exigences pour la radiographie gnrale (CEI 62494-1:2008) Medizinische elektrische Gerte - Dosisindikator digitaler Rntgenbildsysteme - Teil 1: Definitionen und Anforderungen fr die allgemeine Radiographie (IEC 624
8、94-1:2008) This European Standard was approved by CENELEC on 2008-10-01. CENELEC 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 bibli
9、ographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibilit
10、y of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece
11、, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. BS EN 62494-1:2008EN 62494-1:2008 2 Foreword The text of document 62B/680/CDV, future edition 1 of IEC
12、62494-1, prepared by SC 62B, Diagnostic imaging equipment, of IEC TC 62, Electrical equipment in medical practice, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 62494-1 on 2008-10-01. The following dates were fixed: latest date by which the EN has to be implemented
13、 at national level by publication of an identical national standard or by endorsement (dop) 2009-07-01 latest date by which the national standards conflicting with the EN have to be withdrawn (dow) 2011-10-01 In this standard, the following print types are used: requirements, compliance with which c
14、an be tested, and definitions: in roman type; explanations, advice, notes, general statements, exceptions and references: in smaller type; TERMS DEFINED IN CLAUSE 3 OF THIS STANDARD, IN EN 60601-1 OR IN IEC/TR 60788, AS REFERENCED IN THE INDEX OF DEFINED TERMS: SMALL CAPITALS. Annex ZA has been adde
15、d by CENELEC. _ Endorsement notice The text of the International Standard IEC 62494-1:2008 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated: IEC 60601-1 NOTE Harmonized
16、 as EN 60601-1:2006 (not modified). IEC 60601-2-43 NOTE Harmonized as EN 60601-2-43:2000 (not modified). IEC 62220-1 NOTE Harmonized as EN 62220-1:2004 (not modified). IEC 62220-1-2 NOTE Harmonized as EN 62220-1-2:2007 (not modified). _ BS EN 62494-1:2008 3 EN 62494-1:2008 Annex ZA (normative) Norma
17、tive references to international publications with their corresponding European publications The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced d
18、ocument (including any amendments) applies. NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies. Publication Year Title EN/HD Year IEC/TR 60788 2004 Medical electrical equipment - Glossary of defined terms - - BS EN 62494-1
19、:2008 2 62494-1 IEC:2008 CONTENTS FOREWORD.3 INTRODUCTION.5 1 Scope.7 2 Normative references .7 3 Terms and definitions .7 4 Requirements .9 4.1 Creation of ORIGINAL DATA9 4.2 Determination of the RELEVANT IMAGE REGION and the VALUE OF INTEREST .9 4.3 Requirements for the EXPOSURE INDEX .10 4.4 Cali
20、bration of the EXPOSURE INDEX .10 4.5 Determination of the CALIBRATION FUNCTION .11 4.6 Determination of the INVERSE CALIBRATION FUNCTION 11 4.7 Requirements for the DEVIATION INDEX11 Annex A (informative) Details on the rationale, properties and use of the EXPOSURE INDEX 13 Annex B (informative) De
21、tails on the rationale, properties and use of the DEVIATION INDEX 17 Annex C (normative) Beam conditions to be used for calibration18 Bibliography19 Terminology Index of defined terms .20 Figure A.1 Example of an ORIGINAL DATA radiograph with an example of the RELEVANT IMAGE REGION outlined .14 Figu
22、re A.2 Histogram of the ORIGINAL DATA for the radiograph shown in Figure A.1 15 Figure A.3 Relative IMAGE RECEPTOR AIR KERMA required to produce a fixed detector response for the four x-ray beam qualities defined in ISO 9236-1 .16 BS EN 62494-1:200862494-1 IEC:2008 3 INTERNATIONAL ELECTROTECHNICAL C
23、OMMISSION _ MEDICAL ELECTRICAL EQUIPMENT EXPOSURE INDEX OF DIGITAL X-RAY IMAGING SYSTEMS Part 1: Definitions and requirements for general radiography FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnic
24、al committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, T
25、echnical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, gover
26、nmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions o
27、r agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees. 3) IEC Publications have the form of recommendations for internationa
28、l use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to
29、promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly i
30、ndicated in the latter. 5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall att
31、ach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fee
32、s) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publicati
33、on. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 62494-1 has been prepared by subcommittee 62B: Diagnostic im
34、aging equipment, of IEC technical committee 62: Electrical equipment in medical practice. The text of this standard is based on the following documents: Enquiry draft Report on voting 62B/680/CDV 62B/703/RVCFull information on the voting for the approval of this standard can be found in the report o
35、n voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. BS EN 62494-1:2008 4 62494-1 IEC:2008 In this standard, the following print types are used: requirements, compliance with which can be tested, and definitions: in roman type; e
36、xplanations, advice, notes, general statements, exceptions and references: in smaller type; TERMS DEFINED IN CLAUSE 3 OF THIS STANDARD, IN IEC 60601-1 OR IN IEC 60788, AS REFERENCED IN THE INDEX OF DEFINED TERMS: SMALL CAPITALS. A list of all parts of the IEC 62494 series, published under the genera
37、l title Medical electrical equipment Exposure index of digital X-ray imaging systems, can be found on the IEC website. The committee has decided that the contents of this publication will remain unchanged until the maintenance result date indicated on the IEC web site under “http:/webstore.iec.ch“ i
38、n the data related to the specific publication. At this date, the publication will be reconfirmed, withdrawn, replaced by a revised edition, or amended. BS EN 62494-1:200862494-1 IEC:2008 5 INTRODUCTION The direct connection between the level of detector exposure and optical density is well establis
39、hed in film-screen radiology. This is not the case in digital radiography, where almost always a constant image characteristic is achieved using automatic image processing. Consequently, deviations from the intended exposure, i.e., over- and underexposure, are not noticeable by a corresponding devia
40、tion in image brightness. While considerable underexposure results in an increased level of noise, the more alarming aspect (from a radiation protection point of view) is that overexposure cannot be recognized easily in the displayed image. Therefore, various manufacturers of digital radiography sys
41、tems have introduced so-called exposure indicators for their equipment. These are numbers, determined from the original image data of each image taken, which allow conclusions about the level of the exposure at the image receptor. However, the exposure indicators are manufacturer or system specific,
42、 i.e. they differ for the systems of different manufacturers in their definition and scaling. A unified EXPOSURE INDEX for all digital radiography systems is needed to simplify its usage, e.g. for the establishment of exposure guidelines, particularly when systems of different manufacturers are used
43、 within the same department. This standard defines such a concept of the EXPOSURE INDEX. What is laid down here refers to the definition, the scale and the general requirements for the EXPOSURE INDEX. The process of its calculation in detail (software algorithm) is excluded from this standard as to
44、not obstruct technical progress. The EXPOSURE INDEX allows the OPERATOR to judge if an image was taken at a detector exposure level suitable for the intended level of image quality. It is important to note that the EXPOSURE INDEX, as defined in this standard, is derived from the image signal, which
45、in turn is usually related to the energy absorbed in the detector, i.e. the detector dose, but not directly to the air kerma at the image receptor. The relation to IMAGE RECEPTOR AIR KERMA (air kerma at the detector surface) is introduced only at one radiation quality through calibration. However, t
46、his definition is appropriate as the image quality in digital radiography is determined mainly by the signal-to-noise level, which in turn is determined by the absorbed energy. Annex A provides more details on the rationale, properties and use of the EXPOSURE INDEX. The level of detector exposure ne
47、eded to obtain a suitable level of image quality may vary depending on body part, view, or the x-ray imaging system used, as may the appropriate EXPOSURE INDEX. This standard introduces a second parameter, called DEVIATION INDEX, which quantifies the deviation of an actual EXPOSURE INDEX from the ap
48、propriate EXPOSURE INDEX (called TARGET EXPOSURE INDEX). While this parameter does not relate to the image receptor dose on an absolute scale, it allows the operator an easy check whether the exposure is considered acceptable for the specific imaging task. Annex B provides more details on the ration
49、ale, properties and use of the DEVIATION INDEX. The storage of the EXPOSURE INDEX (and the DEVIATION INDEX) together with the image data, e.g., in a DICOM tag field, allows the documentation and communication of the image receptor dose level in clinical practice. The EXPOSURE INDEX does not obviate the use of dose parameters that describe the patients exposure to radiation, such as, for example, the REFERENCE AIR KERMA or the kerma-area product. Bec
