Ultrasonics - Field characterization - Test methods for the determination of thermal and mechanical indices related to medical diagnostic ultrasonic fields

IEC 62359:2010 is applicable to medical diagnostic ultrasound fields. It establishes:
- parameters related to thermal and non-thermal exposure 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.
This second edition cancels and replaces the first edition, published in 2005. It constitutes a technical revision. Major changes with respect to the previous edition include the following:
- The methods of determination set out in the first edition of this standard were based on those contained in the American standard for Real-Time Display of Thermal and Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment (ODS) and were intended to yield identical results. While this second edition also follows the ODS in principal and uses the same basic formulae and assumptions (see Annex A), it contains a few significant modifications which deviate from the ODS.
- One of the primary issues dealt with in preparing this second edition of IEC 62359 was "missing" TI equations. In Edition 1 there were not enough equations to make complete "at-surface" and "below-surface" summations for TIS and TIB in combined-operating modes. Thus major changes with respect to the previous edition are related to the introduction of new calculations of thermal indices to take into account both "at-surface" and "below-surface" thermal effects. The contents of the corrigendum of March 2011 have been included in this copy.

Ultrasons - Caractérisation du champ - Méthodes d'essais pour la détermination d'indices thermique et mécanique des champs d'ultrasons utilisés pour le diagnostic médical

La CEI 62359:2010 est applicable aux champs d'ultrasons utilisés pour le diagnostic médical. Elle définit:
- des paramètres relatifs aux aspects thermiques et non thermiques des champs ultrasonores de diagnostic;
- des méthodes de détermination d'un paramètre d'exposition relatif à l'échauffement dans les modèles théoriques équivalents aux tissus, résultant de l'absorption d'ultrasons;
- des méthodes de détermination d'un paramètre d'exposition approprié pour certains effets non thermiques.
Cette deuxième édition annule et remplace la première édition publiée en 2005. Elle constitue une révision technique. Les modifications majeures par rapport à l'édition précédente incluent ce qui suit:
- Les méthodes de détermination présentées dans la première de la présente norme étaient basées sur celles contenues dans la Norme américaine relative à l'affichage en temps réel des Indices d'émission acoustiques thermique et mécanique des appareils de diagnostics à ultrasons (ODS) et devaient fournir des résultats identiques. Bien que l'édition seconde suive également l'ODS dans le principe et utilise les mêmes formules et hypothèses fondamentales (voir Annexe A), elle comporte quelques modifications significatives s'écartant de l'ODS.
- L'une des principales questions traitées lors de l'élaboration de l'édition seconde de la CEI 62359 norme faisait référence aux équations de TI "manquantes". Elles n'étaient pas suffisantes dans l'édition 1 afin d'effectuer des sommations "à la surface" et "sous la surface" complètes pour TIS et TIB en modes de fonctionnement combinés. Ainsi, les modifications majeures par rapport à l'édition précédente sont liées à l'introduction de nouveaux calculs d'indices thermiques pour prendre en compte les effets thermiques "à la surface" et "sous la surface". Le contenu du corrigendum de mars 2011 a été pris en considération dans cet exemplaire.

General Information

Status
Published
Publication Date
26-Oct-2010
Technical Committee
Current Stage
PPUB - Publication issued
Start Date
27-Oct-2010
Completion Date
27-Oct-2010
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IEC 62359
Edition 2.0 2010-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Ultrasonics – Field characterization – Test methods for the determination of
thermal and mechanical indices related to medical diagnostic ultrasonic fields
Ultrasons – Caractérisation du champ – Méthodes d'essai pour la détermination
d'indices thermique et mécanique des champs d'ultrasons utilisés pour le
diagnostic médical
IEC 62359:2010
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 62359
Edition 2.0 2010-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Ultrasonics – Field characterization – Test methods for the determination of
thermal and mechanical indices related to medical diagnostic ultrasonic fields
Ultrasons – Caractérisation du champ – Méthodes d'essai pour la détermination
d'indices thermique et mécanique des champs d'ultrasons utilisés pour le
diagnostic médical
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX
ICS 17.140.50 ISBN 978-2-88912-181-6
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 62359  IEC:2010
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope ............................................................................................................................... 7

2 Normative references ....................................................................................................... 7

3 Terms and definitions ....................................................................................................... 8

4 List of symbols ............................................................................................................... 21

5 Test methods for determining the mechanical index and the thermal index ..................... 23

5.1 General ................................................................................................................. 23

5.2 Determination of mechanical index ........................................................................ 23

5.2.1 Determination of attenuated peak-rarefactional acoustic pressure ............. 23

5.2.2 Calculation of mechanical index ................................................................ 23

5.3 Determination of thermal index – general .............................................................. 24

5.4 Determination of thermal index in non-scanning mode ........................................... 24

5.4.1 Determination of soft tissue thermal index for non-scanning modes ........... 24

5.4.2 Determination of bone thermal index, TIB, for non-scanning modes ........... 25

5.5 Determination of thermal index in scanning modes ................................................ 26

5.5.1 Determination of soft tissue thermal index for scanning modes .................. 26

5.5.2 Determination of bone thermal index for scanning modes .......................... 27

5.6 Calculations for combined-operating mode ............................................................ 28

5.6.1 Acoustic working frequency ....................................................................... 28

5.6.2 Thermal index ............................................................................................ 28

5.6.3 Mechanical index ....................................................................................... 29

5.7 Summary of measured quantities for index determination ...................................... 29

Annex A (informative) Rationale and derivation of index models ......................................... 30

Annex B (informative) Guidance notes for measurement of output power in combined

modes, scanning modes and in 1 cm × 1 cm windows ........................................................... 51

Annex C (informative) The contribution of transducer self-heating to the temperature

rise occurring during ultrasound exposure ............................................................................. 58

Annex D (informative) Guidance on the interpretation of TI and MI ...................................... 59

Annex E (informative) Differences from IEC 62359 Edition 1 ................................................ 61

Bibliography .......................................................................................................................... 64

Figure 1 – Schematic diagram of the different planes and lines in an ultrasonic field

(modified from IEC 61828 and IEC 62127-1) ........................................................................ 12

Figure A.1 – Focusing transducer with a f-number of about 7 ................................................ 37

Figure A.2 – Strongly focusing transducer with a low f-number of about 1 ............................. 37

Figure A.3 – Focusing transducer (f-number ≈ 10) with severe undulations close to the

transducer ............................................................................................................................ 38

Figure A.4 – Focusing transducer ......................................................................................... 44

Figure A.5 – Focusing transducer with smaller aperture than that of Figure A.4 .................... 44

Figure A.6 – Focusing transducer with a weak focus near z ................................................ 45

Figure A.7 – Weakly focusing transducer .............................................................................. 45

Figure B.1 – Example of curved linear array in scanning mode ............................................. 53

Figure B.2 – Suggested 1 cm × 1 cm square-aperture mask.................................................. 56

---------------------- Page: 4 ----------------------
62359  IEC:2010 – 3 –

Figure B.3 – Suggested orientation of transducer, mask aperture and RFB target ................. 56

Figure B.4 – Suggested orientation of transducer and 1 cm-square RFB target ..................... 57

Table 1 – Summary of combination formulae for each of the THERMAL INDEX categories ......... 28

Table 2 – Summary of the acoustic quantities required for the determination of the

indices .................................................................................................................................. 29

Table A.1 – Thermal index categories and models ................................................................ 36

Table A.2 – Consolidated thermal index formulae ................................................................. 41

Table E.1 – Summary of differences ..................................................................................... 63

---------------------- Page: 5 ----------------------
– 4 – 62359  IEC:2010
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

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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.

This second edition cancels and replaces the first edition, published in 2005. It constitutes a

technical revision.
Major changes with respect to the previous edition include the following:

• The methods of determination set out in the first edition of this standard were based on

those contained in the American standard for Real–Time Display of Thermal and

Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment (ODS) and were

intended to yield identical results. While this second edition also follows the ODS in

principal and uses the same basic formulae and assumptions (see Annex A), it contains a

few significant modifications which deviate from the ODS.
---------------------- Page: 6 ----------------------
62359  IEC:2010 – 5 –

• One of the primary issues dealt with in preparing this second edition of IEC 62359 was

“missing” TI equations. In Edition 1 there were not enough equations to make complete

“at-surface” and “below-surface” summations for TIS and TIB in combined-operating

modes. Thus major changes with respect to the previous edition are related to the

introduction of new calculations of thermal indices to take into account both "at-surface"

and "below-surface" thermal effects.
For the specific technical changes involved please see Annex E.
The text of this standard is based on the following documents:
FDIS Report on voting
87/445/FDIS 87/453/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.
In this particular standard, the following print types are used:

– requirements, compliance with which can be tested, and definitions: in roman type

– notes, explanations, advice, introductions, general statements, exceptions, and references: in smaller type

– test specifications: in italic type
– words in bold are defined terms in Clause 3

The committee has decided that the contents of this amendment and the base publication will

remain unchanged until the stability 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.
The contents of the corrigendum of March 2011 have been included in this copy.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
---------------------- Page: 7 ----------------------
– 6 – 62359  IEC:2010
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 that 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 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. While

such increases remain pending, several organizations have published prudent-use
statements.

Under certain conditions specified in IEC 60601-2-37, these indices are displayed on medical

ultrasonic equipment intended for these purposes.
---------------------- Page: 8 ----------------------
62359  IEC:2010 – 7 –
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 exposure 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 1 In Clause 3 of this standard, SI units are used (per ISO/IEC Directives, Part 2, ed. 5, Annex I b) in the

Notes below definitions of certain parameters, such as beam areas and intensities; it may be convenient to use

decimal multiples or submultiples in practice. Users must take care of decimal prefixes used in combination with

the units when using and calculating numerical data. For example, beam area may be specified in cm and

2 2
intensities in W/cm or mW/cm .

NOTE 2 Underlying calculations have been done from 0,25 MHz to 15 MHz for MI and 0,5 MHz to 15 MHz for TI.

NOTE 3 The thermal indices are steady state estimates based on the acoustic output power required to produce

-1 -1
1)

a 1°C temperature rise in tissue conforming to the “homogeneous tissue 0,3 dBcm MHz attenuation model” [1 ]

and may not be appropriate for radiation force imaging, or similar techniques that employ pulses or pulse bursts of

sufficient duration to create a significant transient temperature rise. [2]
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

basic safety and essential performance of ultrasonic medical diagnostic and monitoring

equipment

IEC 61157:2007, Standard means for the reporting of the acoustic output of medical

diagnostic ultrasonic equipment
IEC 61161:2006, Ultrasonics – Power measurement – Radiation force balances and
performance requirements

IEC 61828:2001, Ultrasonics – Focusing transducers – Definitions and measurement methods

for the transmitted fields

IEC 62127-1:2007, Ultrasonics – Hydrophones – Part 1: Measurement and characterization of

medical ultrasonic fields up to 40 MHz
___________
Figures in square brackets refer to Bibliography.
---------------------- Page: 9 ----------------------
– 8 – 62359  IEC:2010

IEC 62127-2:2007, Ultrasonics – Hydrophones – Part 2: Calibration for ultrasonic fields up to

40 MHz

IEC 62127-3:2007, Ultrasonics – Hydrophones – Part 3: Properties of hydrophones for

ultrasonic fields up to 40 MHz
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 62127-1:2007,

IEC 62127-2:2007, IEC 62127-3:2007, IEC 61157:2007 and IEC 61161:2006 (several of which

are repeated below for convenience) apply.

NOTE Units below definitions are given is SI units as per ISO/IEC Directives, Part 2, ed. 5, Annex I b). Users

must be alert to possible need to convert units when using this standard in situations where data are received in

units that are different from those used in the SI system.
3.1
acoustic attenuation coefficient

coefficient intended to account for ultrasonic attenuation of tissue between the external

transducer aperture and a specified point
NOTE 1 A linear dependence on frequency is assumed.
-1 1

NOTE 2 Acoustic attenuation coefficient is expressed in decibels per metre per hertz (dB m Hz ).

3.2
acoustic absorption coefficient

coefficient intended to account for ultrasonic absorption of tissue in the region of interest

NOTE 1 A linear dependence on frequency is assumed.
-1 1

NOTE 2 Acoustic absorption coefficient is expressed in neper per metre per hertz (Np m Hz ).

3.3
acoustic repetition period
arp

time interval between corresponding points of consecutive cycles for continuous wave

systems

NOTE 1 The acoustic repetition period is equal to the pulse repetition period for non-automatic scanning

systems and to the scan repetition period for automatic scanning systems.
NOTE 2 The acoustic repetition period is expressed in seconds (s).
[IEC 62127-1:2007, definition 3.2, modified]
3.4
acoustic working frequency

frequency 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 The signal is analysed using either the zero-crossing acoustic-working frequency technique or a

spectrum analysis method. Specific acoustic-working frequencies are defined in 3.4.1 and 3.4.2.

NOTE 2 For pulsed waveforms the acoustic-working frequency shall be measured at the position of maximum

pulse-pressure-squared integral.
NOTE 3 Acoustic frequency is expressed in hertz (Hz).
[IEC 62127-1:2007, definition 3.3, modified]
---------------------- Page: 10 ----------------------
62359  IEC:2010 – 9 –
3.4.1
zero-crossing acoustic-working frequency
awf

number of consecutive half-cycles (irrespective of polarity) divided by twice the time between

the commencement of the first half-cycle and the end of the n-th half-cycle

NOTE 1 Any half-cycle in which the waveform shows evidence of phase change shall not be counted.

NOTE 2 The measurement should be performed at terminals in the receiver, that are as close as possible to the

receiving transducer (hydrophone) and, in all cases, before rectification.

NOTE 3 This frequency is determined according to the procedure specified in IEC/TR 60854 [3].

NOTE 4 This frequency is intended for continuous-wave systems only.
3.4.2
arithmetic-mean acoustic-working frequency
awf

arithmetic mean of the most widely separated frequencies f and f , within the range of three

1 2

times f , at which the magnitude of the acoustic pressure spectrum is 3 dB below the peak

magnitude
NOTE 1 This frequency is intended for pulse-wave systems only.
NOTE 2 It is assumed that f < f .
1 2

NOTE 3 If f is not found within the range < 3 f , f is to be understood as the lowest frequency above this range

2 1 2
at which the spectrum magnitude is -3 dB from the peak magnitude.
3.5
attenuated bounded-square output power
P (z)
1x1,α
The maximum value of the attenuated output power passing through any one square
centimeter of the plane perpendicular to the beam axis at depth z

NOTE 1 At z = 0 (the transducer surface) P (z) becomes the bounded-square output power, that is, at z = 0,

1x1,α
P = P .
1x1,α 1x1
NOTE 2 Attenuated bounded-square output power is expressed in watts (W).
3.6
attenuated output power
P (z)

value of the acoustic output power after attenuation, at a specified distance from the

external transducer aperture, and given by
(-a z f /10dB)
awf
P (z) = P 10 (1)
where
a is the acoustic attenuation coefficient;

z is the distance from the external transducer aperture to the point of interest;

f is the acoustic working frequency;
awf
P is the output power measured in water.
NOTE 1 Attenuated output power is expressed in watts (W).

NOTE 2 In the case of stand-offs the P should represent the output power emanating from the stand-off.

3.7
attenuated peak-rarefactional acoustic pressure
p (z)
r,a

value of the peak-rarefactional acoustic pressure after attenuation, at a specified distance

from the external transducer aperture, and given by
---------------------- Page: 11 ----------------------
– 10 – 62359  IEC:2010
(-a z f /20dB)
awf
p (z) = p (z) 10 (2)
r , α r
where
a is the acoustic attenuation coefficient;

z is the distance from the external transducer aperture to the point of interest;

f is the acoustic working frequency;
awf
p (z) is the peak-rarefactional acoustic pressure measured in water.

NOTE Attenuated peak-rarefactional acoustic pressure is expressed in pascals (Pa).

3.8
attenuated pulse-intensity integral
pii (z)

value of the pulse-intensity integral after attenuation, at a specified distance from the

external transducer aperture, and given by
(-a z f /10dB)
awf
pii (z) = pii 10 (3)
where
a is the acoustic attenuation coefficient;

z is the distance from the external transducer aperture to the point of interest;

f is the acoustic working frequency;
awf
pii is the pulse-intensity integral measured in water.

NOTE Attenuated pulse-intensity integral is expressed in joules per metre squared, (J m ).

3.9
attenuated spatial-average temporal-average intensity
I (z)
sata,a

value of the spatial-average temporal-average intensity after attenuation, at a specified

distance from the external transducer aperture, and given by
(-a z f /10dB)
awf
I (z) = I 10 (4)
sata ,α sata
where
a is the acoustic attenuation coefficient;

z is the distance from the external transducer aperture to the point of interest;

f is the acoustic working frequency;
awf
I is the spatial-average temporal-average intensity, at a specified distance z
sata
measured in water.

NOTE Attenuated spatial-average temporal-average intensity is expressed in watts per metre squared, (W m ).

3.10
attenuated spatial-peak temporal-average intensity
I (z)
spta,a

value of the spatial-peak temporal-average intensity after attenuation, at a specified

distance from the external transducer aperture, and given by
(-a z f /10dB)
awf
I (z) = I 10 (5)
spta ,α spta
where
---------------------- Page: 12 ----------------------
62359  IEC:2010 – 11 –
a is the acoustic attenuation coefficient;

z is the distance from the external transducer aperture to the point of interest;

f is the acoustic working frequency;
awf

I is the spatial-peak temporal-average intensity, at a specified distance z measured in

spta
water.

NOTE Attenuated spatial-peak temporal-average intensity is expressed in watts per metre squared, (W m ).

3.11
attenuated temporal-average intensity
I (z)
ta,a

value of the temporal-average intensity after attenuation, at a specified distance from the

external transducer aper
...

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