1、 IEC/TR 62799 Edition 1.0 2013-09 TECHNICAL REPORT Models for evaluation of thermal hazard in medical diagnostic ultrasonic fields IEC/TR 62799:2013(E) THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2013 IEC, Geneva, Switzerland All rights reserved. Unless otherwise specified, no part of this pub
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9、ic fields INTERNATIONAL ELECTROTECHNICAL COMMISSION X ICS 11.040.50 PRICE CODE ISBN 978-2-8322-1099-4 Registered trademark of the International Electrotechnical Commission Warning! Make sure that you obtained this publication from an authorized distributor. 2 TR 62799 IEC:2013(E) CONTENTS FOREWORD .
10、 4 1 Scope 6 2 Normative references 6 3 Terms and definitions 6 4 Background . 10 4.1 General 10 4.2 Limitations of the existing standard 11 4.2.1 Linear display . 11 4.2.2 Equilibrium temperature 12 4.2.3 Tissue parameters 12 4.2.4 Transducer self-heating 12 4.2.5 Safety limits 12 5 Options for imp
11、rovement of the existing standard 13 5.1 General 13 5.2 Exponential display of the current TI 13 5.2.1 Theory 13 5.2.2 Illustrative results for the new thermal index display . 15 5.2.3 Advantages of the new display . 15 5.2.4 Shortcomings of the new display . 16 5.3 Replacement of the TI with the th
12、ermally equivalent time index (TETI) . 16 5.3.1 Theory 16 5.3.2 Illustrative results for the TETI 20 5.3.3 Advantages of the TETI. 22 5.3.4 Shortcomings of the TETI 22 5.4 Replacement of the TI with the time to threshold (TT). 23 5.4.1 Theory 23 5.4.2 Illustrative results for the TT 24 5.4.3 Advanta
13、ges of the TT 27 5.4.4 Shortcomings of the TT . 27 5.5 Replacement of the TI with the safe use time (SUT) . 28 5.5.1 Theory 28 5.5.2 Illustrative results for the SUT . 30 5.5.3 Advantages of the SUT 33 5.5.4 Shortcomings of the SUT . 33 5.6 Replacement of the TI with the thermally equivalent time di
14、splayed (TETD) . 34 5.6.1 Theory 34 5.6.2 Illustrative results for the TETD . 35 5.6.3 Advantages of the TETD . 38 5.6.4 Shortcomings of the TETD 39 6 Summary . 40 7 Recommendations . 41 7.1 General 41 7.2 Thermally equivalent time index . 41 7.3 Other models . 41 Bibliography 42 TR 62799 IEC:2013(E
15、) 3 Figure 1 Comparison of the values of thermal index that would be displayed under the proposed definition, TI new , with that displayed currently, TI cur. 15 Figure 2 Expanded view of the comparison of Figure 1 for smaller values of TI cur15 Figure 3 Thermal-equivalent core temperature elevations
16、 vs time 18 Figure 4 Temperature-time curve (solid line) that represents a conservative boundary for non-foetal exposure durations, particularly for exposure durations of less than 5 s 19 Figure 5 Thermally equivalent time index (solid curves) vs foetal exposure duration for TI = 1, 2, 3 and 4 . 21
17、Figure 6 Temperature rise for distance (z 0 3 cm) for four models as a function of US exposure time . 25 Figure 7 Relation between TT (time to threshold) and power parameters that give a temperature rise of T thr= 4 C 26 Figure 8 The ratio of temperature rise to acoustic absorption coefficient, T/,
18、vs exposure duration for the non-scanning soft tissue model with P a= 100 mW. . 27 Figure 9 A typical example of temperature rise due to diagnostic ultrasound 29 Figure 10 Values of temperature rise as a function of insonation time 31 Figure 11 The thermal load as a function of time and f-number 32
19、Figure 12 A comparison of thermally equivalent times (t 43 ) for the temperature profiles shown in Figure 6 . 36 Figure 13 Probability of birth defect or kidney necrosis as a function of thermally equivalent time (t 43 ) . 37 Figure 14 Probabilities of kidney necrosis estimated for the thermally equ
20、ivalent times (t 43 ) shown in Figure 12 38 Figure 15 Probabilities of birth defect estimated for the thermally equivalent times (t 43 ) shown in Figure 12 . 39 Table 1 Thermally equivalent time thresholds for chronic damage in various tissues, t 43 ; see 21. 20 Table 2 Foetal exposure durations for
21、 a thermally equivalent time index value of 1 22 Table 3 Non-foetal exposure durations for a thermally equivalent time index value of 1 . 22 Table 4 SUT values when including and ignoring the contribution of temperatures lower than T maxfor the four exposure conditions and the corresponding values o
22、f T max32 Table 5 Values of W, W a , and T maxfor the case of SUT = 500 s. . 33 Table 6 Comparison of significant characteristics of the possible replacements for the TI. . 40 4 TR 62799 IEC:2013(E) INTERNATIONAL ELECTROTECHNICAL COMMISSION _ MODELS FOR EVALUATION OF THERMAL HAZARD IN MEDICAL DIAGNO
23、STIC ULTRASONIC FIELDS 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 concerning
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33、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. The main task of IEC technical committees is to prepare International Standards. However, a technical co
34、mmittee may propose the publication of a technical report when it has collected data of a different kind from that which is normally published as an International Standard, for example “state of the art“. IEC 62799, which is a technical report, has been prepared by IEC technical committee 87: Ultras
35、onics. The text of this technical report is based on the following documents: Enquiry draft Report on voting 87/510/DTR 87/537/RVC Full information on the voting for the approval of this technical report can be found in the report on voting indicated in the above table. This publication has been dra
36、fted in accordance with the ISO/IEC Directives, Part 2. TR 62799 IEC:2013(E) 5 Terms appearing in bold print in the text are defined in Clause 3 of this technical report. The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the I
37、EC 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. A bilingual version of this publication may be issued at a later date. 6 TR 62799 IEC:2013(E) MODELS FOR
38、 EVALUATION OF THERMAL HAZARD IN MEDICAL DIAGNOSTIC ULTRASONIC FIELDS 1 Scope This technical report provides background information for users of IEC 62359 to understand the relative merits of several of the potential replacements for the thermal index (TI) as described in IEC 60601-2-37 and IEC 6235
39、9. The report discusses: parameters related to thermal aspects of diagnostic ultrasonic fields; methods for the determination of an exposure parameter relating to temperature rise in theoretical tissue-equivalent models, resulting from absorption of ultrasound. The report is intended to be used by:
40、those involved in the development and maintenance of IEC 62359; manufacturers of medical electrical equipment for risk assessment; health care regulatory authorities, test houses and other organizations responsible for implementing standards for medical electrical equipment. 2 Normative references T
41、he following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 6060
42、1-2-37:2007, Medical electrical equipment Part 2-37: Particular requirements for the basic safety and essential performance of ultrasonic medical diagnostic and monitoring equipment IEC 62127-1:2007, Ultrasonics Hydrophones Part 1: Measurement and characterization of medical ultrasonic fields up to
43、40 MHz IEC 62127-2, Ultrasonics Hydrophones Part 2: Calibration for ultrasonic fields up to 40 MHz IEC 62359:2010, Ultrasonics Field characterization Test methods for the determination of thermal and mechanical indices related to medical diagnostic ultrasonic fields 3 Terms and definitions For the p
44、urposes of this technical report, the terms and definitions given in IEC 60601-2-37, IEC 62127-1, IEC 62127-2 and IEC 62359, some of which are repeated below for convenience, and the following terms and definitions apply. 3.1 acoustic absorption coefficient quantity intended to account for loss of u
45、ltrasonic energy to tissue at a specified point by mechanisms other than scattering TR 62799 IEC:2013(E) 7 Note 1 to entry: Acoustic absorption coefficient is expressed in nepers per centimetre (Np cm -1 ). Note 2 to entry: The acoustic absorption coefficient must be less than or equal to the acoust
46、ic attenuation coefficient. 3.2 acoustic attenuation coefficient quantity intended to account for reduction of energy of an acoustic wave by all mechanisms involving interaction of the wave and all matter between the source and a specified point Note 1 to entry: Acoustic attenuation coefficient is e
47、xpressed in nepers per centimetre (Np cm -1 ). Note 2 to entry: The acoustic attenuation coefficient must be greater than or equal to the acoustic absorption coefficient. Note 3 to entry: The acoustic attenuation coefficient does not account for geometric attenuation. 3.3 acoustic working frequency
48、f awffrequency of an acoustic signal based on the observation of the output of a hydrophone placed in an acoustic field at the position corresponding to the spatial-peak temporal-peak acoustic pressure Note 1 to entry: The signal is analysed using either the zero-crossing acoustic-working frequency
49、technique or a spectrum analysis technique. Acoustic working frequencies are defined in 3.3.1 and 3.3.2. Note 2 to entry: In a number of cases the present definition is not very helpful or convenient, especially for broadband transducers. In that case a full description of the frequency spectrum should be given in order to enable any frequency-dependent correction to the signal. Note 3 to entry: Acoustic working frequency is expressed in hertz (Hz)
