1、 IEC/TS 61949 Edition 1.0 2007-11 TECHNICAL SPECIFICATIONUltrasonics Field characterization In situ exposure estimation in finite-amplitude ultrasonic beams IEC/TS 61949:2007(E) THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2007 IEC, Geneva, Switzerland All rights reserved. Unless otherwise spec
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9、haracterization In situ exposure estimation in finite-amplitude ultrasonic beams INTERNATIONAL ELECTROTECHNICAL COMMISSION V ICS 17.140.50 PRICE CODE ISBN 2-8318-9463-8 2 TS 61949 IEC:2007(E) CONTENTS FOREWORD.3 INTRODUCTION.5 1 Scope.6 2 Normative references .6 3 Terms and definitions .6 4 List of
10、symbols .10 5 Equipment required 11 6 Test methods .11 6.1 Establishing quasi-linear conditions.11 6.1.1 The local distortion parameter .11 6.1.2 Upper limit for quasi-linear conditions for q 12 6.1.3 Range of applicability for quasi-linear conditions .12 6.2 Measurement procedure for estimated in s
11、itu exposure .13 6.2.1 Identification of quasi-linear conditions13 6.2.2 Tables of limiting mean peak acoustic pressure.14 6.2.3 Measurement of acoustic quantities under quasi-linear conditions .14 6.2.4 Measurement of the scaling factor .14 6.2.5 Calculation of attenuated acoustic quantities .15 6.
12、3 Uncertainties.16 Annex A (informative) Review of evidence .18 Annex B (informative) Review of alternative methods for managing finite-amplitude effects during field measurement 21 Annex C (informative) Parameters to quantify nonlinearity.23 Annex D (informative) Tables of upper limits for mean pea
13、k acoustic pressure for quasi-linear conditions26 Bibliography30 Figure 1 Flow diagram for obtaining values of attenuated acoustic quantities.13 Table A.1 Experimental evidence of nonlinear loss associated with the propagation of ultrasound pulses under diagnostic conditions in water.19 Table A.2 Th
14、eoretical evidence of nonlinear loss associated with the propagation of ultrasound pulses under diagnostic conditions in water.19 Table B.1 Methods for estimation of in-situ exposure in nonlinear beams.22 Table C.1 Parameters for quantification of nonlinearity in an ultrasonic field23 Table D.1 The
15、upper limit for mean peak acoustic pressure (MPa) associated with quasi-linear conditions. q 0,5. Acoustic working frequency, f awf= 2,0 MHz .26 Table D.2 The upper limit for mean peak acoustic pressure (MPa) associated with quasi-linear conditions. q 0,5. Acoustic working frequency, f awf= 3,5 MHz
16、.27 Table D.3 The upper limit for mean peak acoustic pressure (MPa) associated with quasi-linear conditions. q 0,5. Acoustic working frequency, f awf= 5,0 MHz .28 Table D.4 The upper limit for mean peak acoustic pressure (MPa) associated with quasi-linear conditions. q 0,5. Acoustic working frequenc
17、y, f awf= 7,0 MHz29 TS 61949 IEC:2007(E) 3 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ ULTRASONICS FIELD CHARACTERIZATION IN SITU EXPOSURE ESTIMATION IN FINITE-AMPLITUDE ULTRASONIC BEAMS FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization c
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30、949, which is a technical specification, has been prepared by IEC technical committee 87: Ultrasonics. 4 TS 61949 IEC:2007(E) The text of this technical specification is based on the following documents: Enquiry draft Report on voting 87/349/DTS 87/364A/RVC Full information on the voting for the app
31、roval of this technical specification 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. This publication is being issued as a technical specification (according to 3.1.1.1 of the IEC/ISO directives,
32、 Part 1) as a “prospective standard for provisional application” in the field of finite-amplitude ultrasonic beams, because there is an urgent need for guidance on how standards in this field should be used to meet an identified need. This document is not to be regarded as an “International Standard
33、”. It is proposed for provisional application so that information and experience of its use in practice may be gathered. Comments on the content of this document should be sent to the IEC Central Office. The committee has decided that the contents of this publication will remain unchanged until the
34、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 transformed into an International standard, reconfirmed, withdrawn, replaced by a revised edition, or amended. TS 61949 IEC:2007(
35、E) 5 INTRODUCTION Acoustic waves of finite amplitude generate acoustic components at higher frequencies than the fundamental frequency. This provides a mechanism for acoustic attenuation which is not significant at lower acoustic pressure, and for which there is substantial experimental and theoreti
36、cal evidence (Tables A.1 and A.2). The generation of harmonic frequency components, and their associated higher attenuation coefficient, can occur very strongly when high amplitude pulses, associated with the use of ultrasound in medical diagnostic applications, propagate through water. This fact is
37、 of importance when measurements of acoustic pressure, made in water, are used to estimate acoustic pressure in another medium, or when intensity derived from hydrophone measurements in water is used to estimate intensity within another medium. In particular, errors occur in the estimation of the ac
38、oustic pressure and intensity in situ, if it is assumed that the propagation of ultrasound through water, and through tissue, is linear. Standards for measurement of frequency-rich pulse waveforms in water are well established (IEC 62127-1). Whilst means to quantify nonlinear behaviour of medical ul
39、trasonic beams are specified, no procedures are given for their use. Since that time IEC 60601-2-37 and IEC 62359 have introduced “attenuated” acoustic quantities, which are derived from measurements in water and intended to enable the estimation of in situ exposure for safety purposes. This Technic
40、al Specification describes means to allow “attenuated” acoustic quantities to be calculated under conditions where the associated acoustic measurements, made in water using standard procedures, may be accompanied by significant finite-amplitude effects. A number of alternative methods have been prop
41、osed (Table B.1).The approach used in this Technical Specification is aligned with the proposal of the World Federation for Ultrasound in Medicine and Biology 1 1) , that “Estimates of tissue field parameters at the point of interest should be based on derated values calculated according to an appro
42、priate specified model and be extrapolated linearly from small signal characterization of source-field relationships.” _ 1)Figures in square brackets refer to the Bibliography. 6 TS 61949 IEC:2007(E) ULTRASONICS FIELD CHARACTERIZATION IN SITU EXPOSURE ESTIMATION IN FINITE-AMPLITUDE ULTRASONIC BEAMS
43、1 Scope This Technical Specification establishes: the general concept of the limits of applicability of acoustic measurements in water resulting from finite-amplitude acoustic effects; a method to ensure that measurements are made under quasi-linear conditions in order to minimise finite-amplitude e
44、ffects, which may be applied under the following conditions: to acoustic fields in the frequency range 0,5 MHz to 15 MHz; to acoustic fields generated by plane sources and focusing sources of amplitude gain up to 12; at all depths for which the maximum acoustic pressure in the plane perpendicular to
45、 the acoustic axis lies on the axis; to both circular and rectangular source geometries; to both continuous-wave and pulsed fields; the definition of an acoustic quantity appropriate for establishing quasi-linear conditions; a threshold value for the acoustic quantity as an upper limit for quasi-lin
46、ear conditions; a method for the estimation of attenuated acoustic quantities under conditions of nonlinear propagation in water. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. Fo
47、r undated references, the latest edition of the referenced document (including any amendments) applies. IEC 61161, Ultrasonics Power Radiation force balances and performance requirements IEC 62127-1:2007 Ultrasonics Hydrophones Part 1: Measurement and characterization of medical ultrasonic fields up
48、 to 40 MHz 3 Terms and definitions For the purposes of this document, the following definitions apply. 3.1 acoustic attenuation coefficient coefficient intended to account for ultrasonic attenuation of tissue between the source and a specified point Symbol: Unit: decibels per centimetre per megahert
49、z, dB cm 1MHz 1IEC 62359, definition 3.1 TS 61949 IEC:2007(E) 7 3.2 acoustic pressure pressure minus the ambient pressure at a particular instant in time and at a particular point in the acoustic field Symbol: p Unit: pascal, Pa IEC 62127-1, definition 3.33, modified 3.3 acoustic working frequency arithmetic mean of the frequencies, f 1and f 2 , at which the acoustic pressure spectrum is 3 dB below the peak value Symbo
