IEC TS 61949:2007

Ultrasonics - Field characterization - In situ exposure estimation in finite-amplitude ultrasonic beams

This Technical 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. 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 effects; - 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-linear conditions; - a method for the estimation of attenuated acoustic quantities under conditions of nonlinear propagation in water.

General Information

• Status: Published
• Publication Date: 26-Nov-2007
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 17.140.50 - Electroacoustics
• Technical Committee: TC 87 - Ultrasonics
• Drafting Committee: WG 14 - TC 87/WG 14
• Current Stage: PPUB - Publication issued
• Start Date: 29-Feb-2008
• Completion Date: 27-Nov-2007

Standards Content (Sample)

IEC/TS 61949
Edition 1.0 2007-11
TECHNICAL
SPECIFICATION
Ultrasonics – Field characterization – In situ exposure estimation
in finite-amplitude ultrasonic beams

IEC/TS 61949:2007(E)
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IEC/TS 61949
Edition 1.0 2007-11
TECHNICAL
SPECIFICATION
Ultrasonics – Field characterization – In situ exposure estimation
in finite-amplitude ultrasonic beams

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
V
ICS 17.140.50 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 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 σ .12
q
6.1.3 Range of applicability for quasi-linear conditions .12
6.2 Measurement procedure for estimated in situ exposure .13
6.2.1 Identification of quasi-linear conditions .13
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
6.3 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 peak acoustic pressure for
quasi-linear conditions .26

Bibliography.30

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 – Theoretical 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 field .23
Table D.1 – The upper limit for mean peak acoustic pressure (MPa) associated with
quasi-linear conditions. σ ≤ 0,5. Acoustic working frequency, f = 2,0 MHz .26

q awf
Table D.2 – The upper limit for mean peak acoustic pressure (MPa) associated with
quasi-linear conditions. σ ≤ 0,5. Acoustic working frequency, f = 3,5 MHz .27

q awf
Table D.3 – The upper limit for mean peak acoustic pressure (MPa) associated with
quasi-linear conditions. σ ≤ 0,5. Acoustic working frequency, f = 5,0 MHz .28

q awf
Table D.4 – The upper limit for mean peak acoustic pressure (MPa) associated with
quasi-linear conditions. σ ≤ 0,5. Acoustic working frequency, f = 7,0 MHz.29
awf
q
TS 61949 © IEC:2007(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS –
FIELD CHARACTERIZATION –
IN SITU EXPOSURE ESTIMATION
IN FINITE-AMPLITUDE ULTRASONIC BEAMS

FOREWORD
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The main task of IEC technical committees is to prepare International Standards. In
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• the required support cannot be obtained for the publication of an International Standard,
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Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 61949, 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 approval 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, 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”. It is proposed for
provisional application so that information and experience of its use in practice may be
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Office.
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
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
TS 61949 © IEC:2007(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
theoretical 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 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
acoustic 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 ultrasonic 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 Technical 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 proposed (Table B.1).The approach used in this
Technical Specification is aligned with the proposal of th
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