EN 62359:2005

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EUROPEAN STANDARD
EN 62359 NORME EUROPÉENNE EUROPÄISCHE NORM
October 2005 CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 62359:2005 E
ICS 17.140.50
English version
Ultrasonics –
Field characterization –
Test methods for the determination of thermal and mechanical indices related to medical diagnostic ultrasonic fields (IEC 62359:2005)
Ultrasons –
Caractérisation du champ –
Essais pour la détermination des indices d'échauffement et mécaniques
des champs d'ultrasons utilisés
pour le diagnostic médical (CEI 62359:2005)
Ultraschall –
Charakterisierung von Feldern - Prüfverfahren für die Ermittlung des thermischen und des mechanischen Indexes bezogen auf medizinisch-diagnostische Ultraschallfelder (IEC 62359:2005)
This European Standard was approved by CENELEC on 2005-09-13. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

at national level by publication of an identical
national standard or by endorsement
(dop)
2006-07-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)
2008-10-01 Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 62359:2005 was approved by CENELEC as a European Standard without any modification. __________

- 3 - EN 62359:2005
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies. Publication Year Title EN/HD Year IEC 60601-2-37 - 1) Medical electrical equipment Part 2-37: Particular requirements for the safety of ultrasonic medical diagnostic and monitoring equipment
EN 60601-2-37 2001 2) IEC 61102 1991 Measurement and characterisation of ultrasonic fields using hydrophones in the frequency range 0,5 MHz to 15 MHz
EN 61102 1993 IEC 61157 1992 Requirements for the declaration of the acoustic output of medical diagnostic ultrasonic equipment
EN 61157 1994 IEC 61161 1992 Ultrasonic power measurement in liquids in the frequency range 0,5 MHz to
25 MHz EN 61161 1994 A1 1998
A1 1998
1) Undated reference. 2) Valid edition at date of issue.

INTERNATIONAL STANDARD IEC62359 First edition2005-04 Ultrasonics – Field characterization – Test methods for the determination of
thermal and mechanical indices related
to medical diagnostic ultrasonic fields
 IEC 2005

Copyright - all rights reserved No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Electrotechnical Commission,
3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, SwitzerlandTelephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch
Web: www.iec.ch X For price, see current cataloguePRICE CODE
Commission Electrotechnique InternationaleInternational Electrotechnical Commission

– 2 – 62359  IEC:2005(E) CONTENTS FOREWORD.3 INTRODUCTION.5
1 Scope.6 2 Normative references.6 3 Terms and definitions.6 4 List of symbols.15 5 Test methods for determining the mechanical index and the thermal index.16 5.1 General.16 5.2 Determination of mechanical index.17 5.3 Determination of thermal index – general.17 5.4 Determination of thermal index in non-scanning mode.17 5.5 Determination of thermal index in scanning mode.19 5.6 Calculations for combined-operating mode.19 5.7 Summary of measured quantities for index determination.20
Annex A (informative)
Relationships with other standards.22 Annex B (informative)
Guidance notes for measurement of output power
in scanning mode.23 Annex C (informative)
Rationale and derivation of index models.27 Annex D (informative)
Guidance on the interpretation of TI and MI.40
Bibliography.41
Figure B.1 – Suggested 1 cm-wide aperture mask.25 Figure B.2 – Suggested orientation of transducer, mask slit and RFB target.25 Figure B.3 – Suggested orientation of transducer and 1 cm RFB target.25 Figure C.1 – Focused transducer with a large aperture.35 Figure C.2 – Focused transducer with smaller aperture (≥1 cm2).35 Figure C.3 – Focused transducer with a weak focus (Aeq > 1 cm2).36 Figure C.4 – Weakly focused transducer.36
Table 1 – Summary of combination formulae for each of the THERMAL INDEX categories.20 Table 2 – Summary of the acoustic quantities required for the determination of the indices.21 Table C.1 – THERMAL INDEX categories and models.29 Table C.2 – Thermal index formulae.33

62359  IEC:2005(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________
ULTRASONICS –
FIELD CHARACTERIZATION –
TEST METHODS FOR THE DETERMINATION OF THERMAL
AND MECHANICAL INDICES RELATED TO
MEDICAL DIAGNOSTIC 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 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 requirements 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 62359 has been prepared by IEC technical committee 87: Ultrasonics The text of this standard is based on the following documents: FDIS Report on voting 87/300/FDIS 87/305/RVD
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. This standard may be used to support the requirements of IEC 60601-2-37.

– 4 – 62359  IEC:2005(E) 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.
A bilingual version of this standard may be issued at a later date.

62359  IEC:2005(E) – 5 –
INTRODUCTION Medical diagnostic ultrasonic equipment is widely used in clinical practice for imaging and monitoring purposes. Equipment normally operates at frequencies in the low megahertz frequency range and comprises an ultrasonic transducer acoustically coupled to the patient and associated electronics. There is an extremely wide range of different types of systems in current clinical practice.
The ultrasound entering the patient interacts with the patient's tissue and this interaction can be considered in terms of both thermal and non-thermal effects. The purpose of this International Standard is to specify methods of determining thermal and non-thermal exposure indices which can be used to help in assessing the hazard caused by exposure to a particular ultrasonic field used for medical diagnosis or monitoring. It is recognised that these indices have limitations and a knowledge of the indices at the time of an examination is not sufficient in itself to make an informed clinical risk assessment. It is intended that these limitations will be addressed in future revisions of this standard and as scientific understanding increases. Under certain conditions specified in IEC 60601-2-37 these indices are displayed on medical ultrasonic equipment intended for these purposes.

– 6 – 62359  IEC:2005(E) ULTRASONICS –
FIELD CHARACTERIZATION –
TEST METHODS FOR THE DETERMINATION OF THERMAL
AND MECHANICAL INDICES RELATED TO
MEDICAL DIAGNOSTIC ULTRASONIC FIELDS
1 Scope This International Standard is applicable to medical diagnostic ultrasound fields. This standard establishes – parameters related to thermal and non-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; – methods for the determination of an exposure parameter appropriate to certain non-thermal effects. NOTE In this standard where multiples or submultiples of SI units are used this is clearly stated and the usage is self-consistent. 2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60601-2-37, Medical electrical equipment – Part 2-37: Particular requirements for the safety of ultrasonic medical diagnostic and monitoring equipment IEC 61102:1991, Measurement and characterisation of ultrasonic fields using hydrophones in the frequency range 0,5 MHz to 15 MHz IEC 61157:1992, Requirements for the declaration of the acoustic output of medical diagnostic ultrasonic equipment IEC 61161:1992, Ultrasonic power measurement in liquids in the frequency range 0,5 MHz to 25 MHz 1)
Amendment 1 (1998) 3 Terms and definitions
For the purposes of this International standard, the terms and definitions given in IEC 61102:1991, IEC 61157:1992 and IEC 61161:1998 (several of which are repeated below for convenience) and the following apply. 3.1
acoustic attenuation coefficient coefficient intended to account for ultrasonic attenuation of tissue between the source and a specified point Symbol: α Unit: decibels per centimetre per megahertz, dB cm–1 MHz–1 ——————— 1) A consolidated edition (1.1) exists, including IEC 61161:1992 and its Amendment 1 (1998).

62359  IEC:2005(E) – 7 –
3.2
acoustic working frequency arithmetic mean of the most widely separated frequencies f1 and f2 at which the amplitude of the pressure spectrum of the acoustic signal is 3 dB lower than the peak amplitude [3.4.2 of IEC 61102:1991, modified] Symbol: fawf Unit: megahertz, MHz 3.3
attenuated output power value of the acoustic output power after attenuation and at a specified distance from the transducer, and given by dB) /10-(awf10 fz PPαα= where α is the acoustic attenuation coefficient; z is the distance from the source to the point of interest; fawf is the acoustic working frequency; P is the output power measured in water.
Symbol: Pα Unit: milliwatts, mW 3.4
attenuated peak-rarefactional acoustic pressure value of the peak-rarefactional acoustic pressure after attenuation and at a specified point, and given by dB)/20(-rr,awf10 )()(fz .zpzpα= where α is the acoustic attenuation coefficient; z is the distance from the source to the point of interest; fawf is the acoustic working frequency; pr(z) is the peak-rarefactional acoustic pressure measured in water. Symbol: pr,α Unit: megapascals, MPa 3.5
attenuated pulse-average intensity value of the acoustic pulse-average intensity after attenuation and at a specified point, and given by dB)/10-(papa,awf10 )(fz zIIαα=

– 8 – 62359  IEC:2005(E) where α is the acoustic attenuation coefficient; z is the distance from the source to the point of interest; fawf is the acoustic working frequency; Ipa(z) is the pulse-average intensity measured in water. Symbol: Ipa,α Unit: watts per centimetre squared, W cm–2 3.6
attenuated pulse-intensity integral value of the pulse-intensity integral after attenuation and at a specified point, and given by dB)/10-(pipi,awf10 fz IIαα= where α is the acoustic attenuation coefficient; z is the distance from the source to the point of interest; fawf is the acoustic working frequency; Ipi is the pulse-intensity integral measured in water. Symbol: Ipi,α Unit: millijoules per centimetre squared, mJ cm–2 3.7
attenuated spatial-peak temporal-average intensity value of the spatial-peak temporal-average intensity after attenuation and at a specified distance z, and given by dB) /10-(zptazpta,awf10 )()(fz zIzIαα= where α is the acoustic attenuation coefficient; z is the distance from the source to the point of interest; fawf is the acoustic working frequency; Izpta(z) is the spatial-peak temporal-average intensity, at a specified distance z measured in water. Symbol: Izpta,α(z) Unit: milliwatts per centimetre squared, mW cm–2 3.8
attenuated temporal-average intensity value of the temporal-average intensity after attenuation and at a specified point, and given by dB)/10(-tata,awf10 )()(fz .zIzIα= where α is the acoustic attenuation coefficient; z is the distance from the source to the point of interest;

62359  IEC:2005(E) – 9 –
fawf is the acoustic working frequency; Ita(z) is the temporal-average intensity measured in water. Symbol: Ita,α(z) Unit: milliwatts per centimetre squared, mW cm–2 3.9
beam area area in a specified plane perpendicular to the beam-alignment axis consisting of all points at which the pulse-intensity integral is greater than a specified fraction of the maximum pulse-intensity integral in that plane [3.6 of IEC 61102:1991, modified] NOTE For measurement purposes the pulse intensity integral can be taken as being proportional to the pulse pressure-squared integral 3.10
beam alignment axis straight line joining the points of maximum pulse intensity integral measured at several different distances in the far field. For the purposes of alignment, this line may be projected to the face of the ultrasonic transducer [3.5 of IEC 61102:1991, modified] 3.11
bone thermal index thermal index for applications, such as foetal (second and third trimester) or neonatal cephalic (through the fontanelle), in which the ultrasound beam passes through soft tissue and a focal region is in the immediate vicinity of bone Symbol: TIB Unit: None NOTE See 5.4.2 and 5.5.2 for methods of determining the bone thermal index. 3.12
bounded output power output power emitted in scanning mode from a region of the active area of the transducer whose width in the scan plane is limited to 1 cm Symbol: P1
Unit: milliwatts, mW 3.13
break-point depth value equal to 1,5 times the equivalent aperture diameter, and given by zbp = 1,5 Deq where Deq is the equivalent aperture diameter. Symbol: zbp Unit: centimetres, cm

– 10 – 62359  IEC:2005(E) 3.14
combined-operating mode mode of operation of an equipment which combines more than one discrete-operating mode [3.6 of IEC 61157:1992, modified] 3.15
cranial-bone thermal index thermal index for applications, such as paediatric and adult cranial applications, in which the ultrasound beam passes through bone near the beam entrance into the body Symbol: TIC Unit: None NOTE See 5.4.3 and 5.5.3 for methods of determining the cranial bone thermal index. 3.16
default setting specific state of control, the ultrasonic diagnostic equipment will enter upon power-up, new patient select or change from non-foetal to foetal applications 3.17
depth for bone thermal index distance from the plane where the –12 dB output beam dimensions are determined along the beam alignment axis to the plane where the product of attenuated output power and attenuated pulse-intensity integral is maximum Symbol: zb
Unit: centimetres, cm 3.18
depth for soft-tissue thermal index distance from the plane where the –12 dB output beam dimensions are determined along the beam alignment axis to the plane at which the lower value of the attenuated output power and the product of the attenuated spatial-peak temporal-average intensity and 1 cm2 is maximized over the distance range equal to, or more than, 1,5 times the equivalent aperture diameter Symbol: zs
Unit: centimetres, cm NOTE In this standard, the restricted definition of spatial-peak temporal-average intensity from 3.49 of IEC 61102:1991 relating to a specified plane is used where spatial-peak temporal-average intensity is replaced by attenuated spatial-peak temporal-average intensity. 3.19
discrete-operating mode mode of operation of ultrasonic diagnostic equipment in which the purpose of the excitation of the ultrasonic transducer or ultrasonic transducer element group is to utilize only one diagnostic methodology [3.7 of IEC 61157:1992]

62359  IEC:2005(E) – 11 –
3.20
equivalent aperture diameter diameter of a circle whose area is the –12 dB output beam area and given by
4aprteqADπ≡ where Aaprt is the –12 dB output beam area. Symbol: Deq Unit: centimetres, cm NOTE This formula gives the diameter of a circle whose area is the –12 dB output beam area. It is used in the calculation of the cranial-bone thermal index and the soft tissue thermal index. 3.21
equivalent beam area value of the area of the acoustic beam at the distance z in terms of power and intensity, and given by ())()(zptazpta,zIPzIzP)z(Aeq=≡αα where Pα(z) is the attenuated output power, at the distance z; Izpta,α(z) is the attenuated spatial-peak temporal-average intensity, at the distance z; P is the output power; Izpta(z)
is the spatial-peak temporal-average intensity, at the distance z; and z is the distance from the source to the specified point. Symbol: Aeq(z) Unit: centimetres squared, cm2 3.22
equivalent beam diameter value of the diameter of the acoustic beam at the distance z in terms of the equivalent beam area, and given by
)(4)(eqeqzAzdπ= where Aeq(z) is the equivalent beam area; z is the distance from the source to the specified point. Symbol: deq(z) Unit: centimetres, cm

– 12 – 62359  IEC:2005(E) 3.23
mechanical index mechanical index is given by
1/2awf,rMICfpMI−=α
where CMI = 1 MPa MHz–1/2;
pr,α is the attenuated peak-rarefactional acoustic pressure; fawf is the acoustic-working frequency.
Symbol: MI Unit: None 3.24
non-scanning mode mode of operation of ultrasonic diagnostic equipment that involves a sequence of ultra-sonic pulses which give rise to ultrasonic scan lines that follow the same acoustic path [3.12 of IEC 61157:1992, modified] 3.25
–12 dB output beam area area of the ultrasonic beam derived from the –12 dB output beam dimensions [3.13 of IEC 61157:1992, modified] Symbol: Aaprt Unit: centimetre squared, cm2 3.26
–12 dB output beam dimensions
dimensions of the ultrasonic beam (–12 dB pulse beam width) in specified directions normal to the beam alignment axis and at the transducer output face [3.14 of IEC 61157:1992, modified] NOTE 1 For reasons of measurement accuracy, the –12 dB output beam dimensions can be derived from measurements at a distance chosen to be as close as possible to the face of the transducer, and if possible no more than 1 mm from the face. NOTE 2 For contact transducers, these dimensions can be taken as the dimensions of the radiating element. Symbol: X, Y Unit: centimetres, cm 3.27
output power time-average ultrasonic power radiated by an ultrasonic transducer into an approximately free field under specified conditions in a specified medium, preferably water [3.5 of IEC 61161:1998] Symbol: P Unit: milliwatts, mW

62359  IEC:2005(E) – 13 –
3.28
peak-rarefactional acoustic pressure maximum of the modulus of the negative instantaneous acoustic pressure in an acoustic field during an acoustic repetition period [3.34 of IEC 61157:1992, modified] Symbol: pr Unit: megapascals, MPa 3.29
prudent-use statement affirmation of the principle advising avoidance of primarily high exposure levels and secondarily long exposure times while acquiring necessary clinical information NOTE See Bibliography [1, 2, 3, 4, 5 ]2) 3.30
pulse beam-width distance between two points, on a specified surface in a specified direction passing through the point of maximum pulse-pressure-squared integral (pi) in that surface, at which the pulse-pressure-squared integral is a specified fraction of the maximum value in that surface [3.18 of IEC 61157:1992, modified] Symbol: d–6 (for pulse beam-width defined at –6dB) Unit: centimetres, cm 3.31
pulse duration 1,25 times the interval between the time when the time integral of intensity in an acoustic pulse at a point reaches 10 % and when it reaches 90 % of the pulse intensity integral [3.30 of IEC 61102:1991, modified] Symbol: td Unit: seconds, s 3.32
pulse-intensity integral time integral of the instantaneous intensity at a particular point in an acoustic field integrated over the acoustic pulse waveform [3.31 of IEC 61102:1991] Symbol: Ipi Unit: millijoules per centimetre squared, mJ cm–2 3.33
pulse-pressure-squared integral time integral of the square of the instantaneous acoustic pressure at a particular point in an acoustic field integrated over the acoustic pulse waveform [3.33 of IEC 61102:1991] ——————— 2) Figures in square brackets refer to the Bibliography.

– 14 – 62359  IEC:2005(E) Symbol: pi Unit: Pascal squared seconds, Pa2s 3.34
pulse repetition rate inverse of the time interval between two successive acoustic pulses [3.35 of IEC 61102:1991, modified] Symbol: prr Unit: hertz, Hz 3.35
scan line ultrasonic scan line for automatic scanning systems, the beam alignment axis either for a particular ultrasonic transducer element group, or for a single or multiple excitation of an ultrasonic transducer or of an ultrasonic transducer element group. [3.27 of IEC 61157:1992] 3.36
scanning mode mode of operation of an ultrasonic diagnostic equipment that involves a sequence of ultrasonic pulses which give rise to scan lines that do not follow the same acoustic path [3.21 of IEC 61157:1992, modified] 3.37
soft tissue thermal index thermal index related to soft tissues
Symbol: TIS Unit: None NOTE 1 See 5.4.1 and 5.5.1 and the following for methods of determination of the soft-tissue thermal index. NOTE 2 For the purposes of this document, soft tissue includes all body tissues and fluids but excludes skeletal tissues. 3.38
spatial-peak temporal-average intensity maximum value of the temporal-average intensity in a specified plane at a specified distance z from the transducer
[3.49 of IEC 61102:1991, modified] Symbol: Izpta(z) Unit: milliwatts per centimetre squared, mW cm–2 NOTE In this standard the restricted definition from 3.49 of IEC 61102 relating to a specified plane is used. 3.39
system medical diagnostic ultrasonic equipment combination of the ultrasound instrument console and the transducer assembly making up a complete system [3.11 of IEC 61157:1992]

62359  IEC:2005(E) – 15 –
3.40
temporal-average intensity time-average of the instantaneous intensity at a particular point in an acoustic field [3.53 of IEC 61102:1991, modified] Symbol: Ita(z) Unit: milliwatts per centimetre squared, mW cm–2 3.41
thermal index ratio of attenuated acoustic power at a specified point to the attenuated acoustic power required to raise the temperature at that point in a specific tissue model by 1 °C
Symbol: TI Unit: None 3.42
transducer assembly transducer housing (probe), any associated electronic circuitry and any liquids contained in the housing and the integral cable which connects the transducer probe to an ultrasound console [see 3.22 of IEC 61157:1992] 3.43
transmit pattern combination of a specific set of transducer beam-forming characteristics (determined by the transmit aperture size, apodization shape and relative timing/phase delay pattern across the aperture, resulting in a specific focal length and direction), and an electrical drive waveform of a specific fixed shape but variable amplitude 3.44
ultrasonic diagnostic equipment medical electrical equipment which is intended for in vivo ultrasonic and monitoring examination for obtaining a medical diagnosis NOTE See also definition 3.11 of IEC 61157:1992: medical diagnostic ultrasonic equipment (or system) – combination of the ultrasound instrument console and the transducer assembly making up a complete diagnostic system. 3.45
ultrasonic transducer device capable of converting electrical energy to mechanical energy and/or mechanical energy to electrical energy, both within the ultrasonic frequency range 4 List of symbols α acoustic attenuation coefficient
Aaprt –12dB output beam area
Aeq(z) equivalent beam area CMI
normalizing coefficient Deq equivalent aperture diameter d–6 pulse beam width deq equivalent beam diameter

– 16 – 62359  IEC:2005(E) fawf
acoustic working frequency Ipa pulse-average intensity Ipa,α attenuated pulse-average intensity Ipi pulse-intensity integral Ipi,α attenuated pulse-intensity integral Ita(z) temporal-average intensity Ita,α(z) attenuated temporal-average intensity Izpta(z) spatial-peak temporal-average intensity Izpta,α(z) attenuated spatial-peak temporal-average intensity MI mechanical index P output power Pα attenuated output power P1 bounded output power pi pulse pressure squared integral pr peak-rarefactional acoustic pressure pr,α attenuated peak-rarefactional acoustic pressure prr pulse repetition rate TI thermal index TIB bone thermal index TIC cranial-bone thermal index TIS soft-tissue thermal index td pulse duration X, Y –12 dB output beam dimensions z
distance from the source to a specified point zb depth for TIB zbp break-point depth zs depth for TIS 5 Test methods for determining the mechanical index and the thermal index 5.1 General This clause defines methods for determining an exposure parameter relating to temperature rise in theoretical tissue-equivalent models, and also an exposure parameter for non-thermal effects. These exposure parameters, referred to as indices, are related to the safety of ultrasonic diagnostic equipment. The indices are intended to be used in IEC 60601-2-37. These indices shall be determined in accordance with 5.2 to 5.5 for a particular ultrasonic field configuration generated by a discrete-operating mode of a specific ultrasonic diagnostic equipment. Background material is given in Annex C. For combined operating modes, the procedures specified in 5.6 shall be used. Acoustic output measurements shall be undertaken using test methods based on the use of hydrophones in accordance with IEC 61102 or the use of radiation force balances for power measurements in accordance with IEC 61161. All such measurements shall be made in water (see also Annex B). The measurement uncertainty is to be determined following [6]. In all cases where bounded output power is determined, the location of the bounding mask or equivalent means (see Annex B) shall be such as to determine the largest value.

62359  IEC:2005(E) – 17 –
The value of the acoustic attenuation coefficient shall be 0,3 dB cm–1 MHz–1. This value is selected as an appropriate attenuating coefficient for a homogeneous model intended to be equivalent to the attenuation in reasonable worst-case conditions of clinical use. The meaning of “reasonable worst case” is taken as that given by the World Federation for Ultrasound in Medicine and Biology [7], namely “that set of tissue properties and dimensions such that less than 2,5 % of patients have a higher calculated temperature increase or other thermal endpoint if their actual tissue properties or thickness differ from those employed in the calculations”. NOTE 1 The attenuation model used is not always applicable. Recent literature suggests that sometimes other models should be used [8]. NOTE 2 Temperature rise in tissue due to transducer surface self heating has not been taken into account in the determination of the thermal index [9]. The –12 dB output beam area may be determined by using a raster scanned hydrophone. 5.2 Determination of mechanical index 5.2.1 Determination of attenuated peak-rarefactional acoustic pressure The calculation of mechanical index requires the determination of the attenuated peak-rarefactional acoustic pressure. This shall be determined at the location of the maximum attenuated pulse-intensity integral. This location should be determined according to the procedures set out in IEC 61102 for the location of peak pulse-pressure-squared integral, with the addition that for all measurement locations an acoustic attenuation coefficient shall be applied to the pulse-pressure squared integral. 5.2.2 Calculation of mechanical index The mechanical index shall be calculated from the expression as defined under 3.23:
1/2awf.r,MICfpMI−=
where CMI = 1 MPa MHz–1/2;
pr,α is the attenuated peak-rarefactional acoustic pressure; fawf is the acoustic-working frequency.
5.3 Determination of thermal index – general The method of determination of the thermal index depends upon whether the field is formed in scanning mode or non-scanning mode. Also for the soft-tissue thermal index in non-scanning mode the method of determination depends on the –12 dB output beam area. Each determination method is set out in the following sections.
5.4 Determination of thermal index in non-scanning mode 5.4.1 Determination of soft-tissue thermal index, TIS, for non-scanning modes When the –12 dB output beam area for the particular transmit pattern satisfies the condition Aaprt ≤ 1,0 cm2 then the soft-tissue thermal index shall be determined following the procedures described in 5.4.1.3. Otherwise, the soft-tissue thermal index shall be determined according to the procedures given in 5.4.1.1 and 5.4.1.2 below. 5.4.1.1 Determination of the depth for TIS, zs, in non-scanning mode The depth for TIS, zs, shall be determined as the depth at which the lower value of Pα and Izpta,α(z) × 1 cm2 is maximized over z, where z > 1,5 Deq. For this determination, Pα shall be in milliwatts and Izpta,α(z) shall be in milliwatts per centimetre squared.

– 18 – 62359  IEC:2005(E) 5.4.1.2 Determination of soft-tissue thermal index, TIS, for Aaprt > 1 cm2 The soft-tissue thermal index, TIS, shall be calculated at the depth for TIS, zs, from: 1TISawf CfPTISα= or TIS2awfszpta,)(CfzITISα= whichever is the lesser,
where CTIS1 = 210 mW MHz;
CTIS2 = 210 mW cm–2 MHz;
Pα is the attenuated output power; fawf is the acoustic working frequency; Izpta,α (zs) is the attenuated spatial-peak temporal-average intensity at the depth of TIS, zs. 5.4.1.3 Determination of soft-tissue thermal index, TIS, for Aaprt ≤ 1 cm2 If the –12 dB output beam area satisfies the condition Aaprt ≤ 1 cm2, the soft-tissue thermal index shall be calculated from 1TISawf CfPTIS= where
CTIS1 = 210 mW MHz;
P is the output power; fawf is the acoustic working frequency. 5.4.2 Determination of bone thermal index, TIB, for non-scanning modes The location of depth for TIB, zb, shall be carried out by determining the variation with the distance of the attenuated output power multiplied by the attenuated pulse-intensity integral. The position of the maximum value of this parameter shall be zb.
The attenuated spatial-peak temporal-average intensity, Izpta,α(zb), at the depth for TIB, zb, shall be calculated from Izpta,α(zb) = Ipi,α(zb)prr where Ipi,α(zb) is the attenuated pulse-intensity integral at the depth for TIB, zb,; prr is the pulse repetition rate. The bone thermal index, TIB, for the model where bone is insonified, shall be calculated from: TIB1zpta,)( )(C zIzPTIBαα=

62359  IEC:2005(E) – 19 –
or
2TIBb)(CzPTIBα= whichever is the lesser;
where CTIB1 = 50 mW cm–1; CTIB2 = 4,4 mW; Pα(zb) is the attenuated output power, at the depth for TIB, zb; Izpta,α(zb) is the attenuated spatial-peak temporal-average intensity, at the depth for TIB, zb.
5.4.3 Determination of cranial-bone thermal index, TIC, for non-scanning modes The cranial-bone thermal index shall be calculated from TIC1eqCDPTIC−= where CTIC = 40 mW cm–1; P is the output power; Deq is the equivalent aperture diameter.
5.5 Determination of thermal index in scanning mode 5.5.1 Determination of soft tissue thermal index, TIS, for scanning modes For each transmit pattern in a scanning mode, the soft-tissue thermal index shall be calculated from 1TISawf1 CfPTIS= where CTIS1 = 210 mW MHz;
P1 is the bounded output power; fawf is the acoustic working frequency.
5.5.2 Determination of bone thermal index, TIB, for scanning mode The determination of bone thermal index for scanning mode shall be identical to that for soft-tissue thermal index for scanning mode, as specified in 5.5.1. 5.5.3 Determination of cranial-bone thermal index, TIC, for scanning mode In a scanning mode the cranial-bone thermal index for a particular transmit pattern shall be calculated with the same parameters as for non-scanning mode 5.6 Calculations for combined-operating mode
5.6.1 Acoustic working frequency In a combined-operating mode with more than one type of transmit pattern employed during the scan period, the acoustic working frequency shall be considered separately for each different transmit pattern as appropriate in calculating the thermal index or the mechanical index.

– 20 – 62359  IEC:2005(E) 5.6.2 Thermal index For combined-operating modes, the thermal index for the contribution of each discrete mode shall be calculated separately and the individual values summed appropriately, as shown in Table 1. The location of the maximum temperature increase is near the surface of the transducer assembly for scanning mode in all three categories, TIS, TIB and TIC. The location of maximum temperature is also near the surface for non-scanning mode for TIS when Aaprt ≤ 1,0 cm2, and for TIC. The location is at greater depth for non-scanning mode for TIB and for TIS when Aaprt > 1,0 cm2. Table 1 summarizes the combination formulae for each of the thermal index categories. Table 1 – Summary of combination formulae for each of the THERMAL INDEX categories Thermal index categories Combining discrete mode values of thermal index TIC, TIS for Aaprt ≤
1,0 cm2 Thermal index at the surface = Σ (thermal index values for all modes) TIB, TIS for Aaprt > 1,0 cm2 Maximum of thermal index at surface or thermal index at depth, i.e. the maximum of Σ (thermal index values for scanning modes)
or
Σ (thermal index values for non-scanning modes)
5.6.3 Mechanical index For combined-operating mode, the mechanical index shall be that for the discrete-operating mode with the largest mechanical index. 5.7 Summary of measured quantities for index determination Table 2 gives a summary of the acoustic quantities required for the determination of each of the defined safety indices. Since attenuated quantities are derived by calculation from associated measured free-field quantities, both attenuated and free-field quantities are included.

62359  IEC:2005(E) – 21 –
Table 2 – Summary of the acoustic quantities required for the determination of the indices Index MI TIS TIS TIS TIB TIB TIC Mode
Scanning Non- scanning Non- scanning Scanning Non- scanning
Aaprt ≤ 1 cm2 Aaprt > 1 cm2
fawf x x x x x x
P
x x
x x P1
x
x
Pα
x
x
Izpta
x
x
Izpta,α
x
x
Ipi x
x
Ipi,α x
x
pr x
pr,α x
Aaprt
x x
x Deq
x
x zs
x
zb
x
z at max. Ipi,α x
– 22 – 62359  IEC:2005(E) Annex A
(informative)
Relationships with other standards
The methods of determinations set out in this standard are intended to yield identical results to those contained in UD-3 Rev.2:2004, Standard for real-time display of thermal and mechanical acoustic output indices on diagnostic ultrasound equipment [33], American Institute of Ultrasound in Medicine/ National Electrical Manufacturers Association.
The models on which these determinations are based and the measurement and calculation rationale are contained in the document UD-3 Rev.2:2004 and in its secondary references. This document has been followed in this standard (see Annex C).

62359  IEC:2005(E) – 23 –
Annex B
(informative)
Guidance notes for measurement of output power
in scanning mode
This annex deals primarily with the exceptions that must be made for scanning modes from the standard acoustic measurement procedures set out in IEC 61102 and IEC 61161. B.1 Measurement of output power, P, in scanning modes This standard requires the measurement of the output power transmitted from the 1 cm linear length of the active array which transmits the most power. This is termed the bounded output power. The following paragraphs provide guidance for the measurement of output power in addition to the requirements set out in IEC 61161 and when these requirements are inappropriate. a) In a combined-operating mode with more than one type of transmit pattern employed during the scan period, the output power may be considered separately for different transmit patterns when necessary to permit accurate measurement of output power and determination of thermal index by combining values appropriately as shown in Table 1. Such an approach may, for example, enable the appropriate acoustic working frequency to be used for each calculation. Caution is needed to ensure that the selected single transmit pattern is identical to that used during combined-operating mode.
b) When performing these measurements in non-scanning mode with the beam scan arrested (when possible), the measured output power should be corrected to compensate for any beam-former related output variability, dependent on beam scan angle and/or linear position. Hydrophone measurements of output power should be performed either with the beam scan arrested, or by making use of a synchronizing system to synchronize the transmitted acoustic signal with the measurement system.
In phased arrays, output power is often increased for non-normal scan angles because of decreased element (reception) sensitivity off axis. c) When performing these measurements in scanning mode, the radiation force balance target and source should be such that the effective beam area intercepts the target over the entire extent of the beam. The alignment of the beam axis, the direction of sensing of the radiation-force balance and the axis of the aperture should be co-linear to within ±10°. The associated error in measurement will depend upon the specific geometry of the transducer and radiation-force-balance target, and no general guidance can be given.
The following sections describe windowing techniques using a 1 cm-wide slit absorber, a 1 cm-wide radiation force balance target or electronic masking techniques. B.2 Creating a 1 cm azimuthal wide window using a mask of absorbing material or a 1 cm-wide radiation force balance target When a radiation force balance target is used to limit the azimuth (image plane) aperture, its geometry and composition should be such as to detect all forward emissions from a 1 cm-wide strip immediately in front of the ultrasonic transducer and not to detect emissions from outside that 1 cm-wide strip.

– 24 – 62359  IEC:2005(E) The two techniques in this section have somewhat different sources of error. Agre
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