IEC-62494-1-2008.pdf
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 électromédicaux Indice d'exposition des systèmes dimagerie numérique à rayonnement X Partie 1: Définitions et exigences pour la radiographie générale IEC 62494-1:2008 Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=Boeing Co/5910770001 Not for Resale, 10/25/2008 03:21:03 MDTNo reproduction or networking permitted without license from IHS -,-,- THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright © 2008 IEC, Geneva, Switzerland All rights reserved. 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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, Technical 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, governmental 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 or 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 international 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 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 indicated 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 attach 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 fees) 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 publication. 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 imaging 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/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 2. Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=Boeing Co/5910770001 Not for Resale, 10/25/2008 03:21:03 MDTNo reproduction or networking permitted without license from IHS -,-,- 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 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 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“ in the data related to the specific publication. At this date, the publication will be reconfirmed, withdrawn, replaced by a revised edition, or amended. Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=Boeing Co/5910770001 Not for Resale, 10/25/2008 03:21:03 MDTNo reproduction or networking permitted without license from IHS -,-,- 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 image 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 point 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 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 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 general 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 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 dire