1、 IEC 62494-1 Edition 1.0 2008-08 INTERNATIONAL STANDARD NORME INTERNATIONALE Medical electrical equipment Exposure index of digital X-ray imaging systems Part 1: Definitions and requirements for general radiography Appareils lectromdicaux Indice dexposition des systmes dimagerie numrique rayonnement
2、 X Partie 1: Dfinitions et exigences pour la radiographie gnrale IEC 62494-1:2008 THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2008 IEC, Geneva, Switzerland All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, el
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16、ur cette publication ou si vous avez des questions, visitez le FAQ du Service clients ou contactez-nous: Email: csciec.ch Tl.: +41 22 919 02 11 Fax: +41 22 919 03 00 IEC 62494-1 Edition 1.0 2008-08 INTERNATIONAL STANDARD NORME INTERNATIONALE Medical electrical equipment Exposure index of digital X-r
17、ay imaging systems Part 1: Definitions and requirements for general radiography Appareils lectromdicaux Indice dexposition des systmes dimagerie numrique rayonnement X Partie 1: Dfinitions et exigences pour la radiographie gnrale INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE
18、INTERNATIONALE R ICS 11.040.50 PRICE CODE CODE PRIX ISBN 2-8318-9944-3 Registered trademark of the International Electrotechnical Commission Marque dpose de la Commission Electrotechnique Internationale 2 62494-1 IEC:2008 CONTENTS FOREWORD.3 INTRODUCTION.5 1 Scope.7 2 Normative references .7 3 Terms
19、 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 Calibration of the EXPOSURE INDEX .10 4.5 Determination of the CALIBRATION FUNCTION .11 4.6 Determination of
20、 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) Details on the rationale, properties and use of the DEVIATION INDEX 17 Annex C (normative) Beam conditions
21、 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 Figure A.2 Histogram of the ORIGINAL DATA for the radiograph shown in Figure A.1 15 Figure A.3 Relative IMAG
22、E RECEPTOR AIR KERMA required to produce a fixed detector response for the four x-ray beam qualities defined in ISO 9236-1 .16 62494-1 IEC:2008 3 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ MEDICAL ELECTRICAL EQUIPMENT EXPOSURE INDEX OF DIGITAL X-RAY IMAGING SYSTEMS Part 1: Definitions and requireme
23、nts for general radiography FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions conce
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33、nt 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 imaging equipment, of IEC technical committee 62: Electrical equipment in medical practice. The text of this standard is ba
34、sed on the following documents: Enquiry draft Report on voting 62B/680/CDV 62B/703/RVC Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part
35、 2. 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; explanations, advice, notes, general statements, exceptions and references: in smaller type; TERMS DEFINED IN CLAUSE 3 OF THIS STANDARD, IN
36、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 general title Medical electrical equipment Exposure index of digital X-ray imaging systems, can be found on the IEC website. The committee has de
37、cided 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“ in the data related to the specific publication. At this date, the publication will be reconfirmed, withdrawn, replaced by a revised edition
38、, or amended. 62494-1 IEC:2008 5 INTRODUCTION The direct connection between the level of detector exposure and optical density is well established in film-screen radiology. This is not the case in digital radiography, where almost always a constant image characteristic is achieved using automatic im
39、age processing. Consequently, deviations from the intended exposure, i.e., over- and underexposure, are not noticeable by a corresponding deviation in image brightness. While considerable underexposure results in an increased level of noise, the more alarming aspect (from a radiation protection poin
40、t of view) is that overexposure cannot be recognized easily in the displayed image. Therefore, various manufacturers of digital radiography systems have introduced so-called exposure indicators for their equipment. These are numbers, determined from the original image data of each image taken, which
41、 allow conclusions about the level of the exposure at the image receptor. However, the exposure indicators are manufacturer or system specific, 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
42、 needed to simplify its usage, e.g. for the establishment of exposure guidelines, particularly when systems of different manufacturers are used 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 g
43、eneral requirements for the EXPOSURE INDEX. The process of its calculation in detail (software algorithm) is excluded from this standard as to 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
44、 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 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 relat
45、ion to IMAGE RECEPTOR AIR KERMA (air kerma at the detector surface) is introduced only at one radiation quality through calibration. However, this 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 t
46、he absorbed energy. Annex A provides more details on the rationale, properties and use of the EXPOSURE INDEX. The level of detector exposure needed 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 IND
47、EX. This standard introduces a second parameter, called DEVIATION INDEX, which quantifies the deviation of an actual EXPOSURE INDEX from the appropriate EXPOSURE INDEX (called TARGET EXPOSURE INDEX). While this parameter does not relate to the image receptor dose on an absolute scale, it allows the
48、operator an easy check whether the exposure is considered acceptable for the specific imaging task. Annex B provides more details on the rationale, 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 ta
49、g 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. Because the relation between patient exposure and detector exposure is influenced by a number of factors that
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