Ultrasonics - Field characterization - Specification and measurement of field parameters for high intensity therapeutic ultrasound (HITU) transducers and systems

IEC TS 62556:2014 is a technical specification applicable to high intensity therapeutic ultrasound (HITU) devices. It specifies the relevant parameters for quantifying the field; the measurement methods at relatively low output levels and methodology for extrapolating these to higher therapeutic level fields; some considerations of sidelobes and pre-focal maxima; and parameters relevant to HITU transducers of different construction and geometry, including non-focusing, focusing with or without lenses, collimated, diverging and convergent transducers, multi-element transducers, scanning transducers and multiple sources. This technical specification is intended to support the ultrasonic measurement requirements given in IEC 60601-2-62. These specifications would have use in quality assurance, safety testing, and the standardization of communications regarding the clinical performance of HITU systems. Where possible, this technical specification incorporates specifications from other related standards. This technical specification does not apply to the following types of devices, which are covered by other standards: lithotripters (see IEC 61846); surgical equipment (see IEC 61847); and physiotherapy devices (see IEC 61689).

General Information

Status
Published
Publication Date
23-Apr-2014
Technical Committee
Current Stage
PPUB - Publication issued
Start Date
24-Apr-2014
Completion Date
24-Apr-2014
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IEC TS 62556:2014 - Ultrasonics - Field characterization - Specification and measurement of field parameters for high intensity therapeutic ultrasound (HITU) transducers and systems
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IEC TS 62556
Edition 1.0 2014-04
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Field characterization – Specification and measurement of field
parameters for high intensity therapeutic ultrasound (HITU) transducers and
systems
IEC TS 62556:2014-04(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TS 62556
Edition 1.0 2014-04
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Field characterization – Specification and measurement of field
parameters for high intensity therapeutic ultrasound (HITU) transducers and
systems
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
ICS 17.140.50 ISBN 978-2-8322-1505-0

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 62556:2014 © IEC 2014
CONTENTS

FOREWORD ........................................................................................................................... 6

INTRODUCTION ..................................................................................................................... 8

1 Scope .............................................................................................................................. 9

2 Normative references ...................................................................................................... 9

3 Terms and definitions .................................................................................................... 10

4 List of symbols .............................................................................................................. 31

5 Independent measurement of total acoustic output power .............................................. 33

6 Acoustic field measurement: equipment ......................................................................... 33

6.1 Hydrophone ..................................................................................................... 33

6.1.1 General .......................................................................................... 33

6.1.2 Sensitivity of a hydrophone ............................................................. 34

6.1.3 Directional response of a hydrophone ............................................. 34

6.1.4 Effective hydrophone radius ........................................................... 34

6.1.5 Choice of the size of a hydrophone active element ......................... 34

6.1.6 Hydrophone pressure limits ............................................................ 35

6.1.7 Hydrophone intensity limits ............................................................. 35

6.1.8 Hydrophone cable length and amplifiers ......................................... 36

6.2 Requirements for positioning and water baths .................................................. 36

6.2.1 General .......................................................................................... 36

6.2.2 Positioning systems ........................................................................ 36

6.2.3 Water bath ...................................................................................... 37

6.3 Requirements for data acquisition and analysis systems .................................. 38

6.4 Requirements and recommendations for ultrasonic equipment being

characterized ................................................................................................... 39

7 Measurement procedure ................................................................................................ 39

7.1 General ............................................................................................................ 39

7.2 Preparation and alignment ............................................................................... 39

7.2.1 Initial adjustment to driving voltage ................................................. 39

7.2.2 Preparation of source transducer .................................................... 40

7.2.3 Aligning an ultrasonic transducer and hydrophone .......................... 41

7.2.4 Beam-axis scan .............................................................................. 41

7.2.5 Measurements to be made at z = z ................................................ 41

7.2.6 Further evaluation for sidelobes and pre-focal maxima ................... 43

7.3 Considerations for scanning transducers and transducers with multiple

sources ............................................................................................................ 44

7.3.1 Automatic scanning transducers ..................................................... 44

7.4 Linear extrapolation of field values ................................................................... 44

7.4.1 General .......................................................................................... 44

7.4.2 Calculation of I ........................................................................... 45

sal

7.4.3 Scaling for sidelobes and pre-focal maxima .................................... 45

7.5 Reporting ......................................................................................................... 45

Annex A (informative) Rationale ........................................................................................... 53

A.1 General ............................................................................................................ 53

A.2 Detailed discussion of difficulties in HITU field measurements ......................... 53

A.2.1 Very high pressures ........................................................................ 53

A.2.2 Very high intensities ....................................................................... 54

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IEC TS 62556:2014 © IEC 2014 – 3 –

A.2.3 Strong focusing .............................................................................. 54

A.2.4 Nonlinear harmonics ....................................................................... 54

A.2.5 Acoustic saturation and nonlinear loss ............................................ 55

A.2.6 Damage to hydrophones may only be apparent at high

pressures ....................................................................................... 55

A.3 Approach of this technical specification ............................................................ 55

Annex B (informative) Assessment of uncertainty in the acoustic quantities obtained

by hydrophone measurements ....................................................................................... 57

B.1 General ............................................................................................................ 57

B.2 Overall (expanded) uncertainty ........................................................................ 57

B.3 Common sources of uncertainty ....................................................................... 57

Annex C (informative) Transducer and hydrophone positioning systems .............................. 59

Annex D (informative) Rationale for I ............................................................................... 60

sal

D.1 General rationale ............................................................................................. 60

D.2 Determination of P using hydrophone measurements and
c,6

extrapolation from linear measurements........................................................... 60

D.3 Alternative determination of P using an aperture in combination with a
c,6

measurement of total acoustic output power .................................................... 60

D.4 Special case of uniformly vibrating spherically shaped transducers .................. 61

Annex E (normative) Propagation and back-propagation methods for field

reconstruction: basic formulae and requirements ........................................................... 62

E.1 Motivation and background .............................................................................. 62

E.2 Theory ............................................................................................................. 62

E.2.1 General .......................................................................................... 62

E.2.2 Fourier projection approach ............................................................ 64

E.2.3 Rayleigh integral approach ............................................................. 67

E.3 Implementation ................................................................................................ 68

E.3.1 General .......................................................................................... 68

E.3.2 Recommendations for hydrophone .................................................. 68

E.3.3 Recommendation for planar scan parameters ................................. 69

E.4 Assessment of uncertainties ............................................................................ 71

Annex F (informative) Propagation and back-propagation methods for field

reconstruction: examples and uses ................................................................................ 73

F.1 Examples ......................................................................................................... 73

F.1.1 Fourier projection example ............................................................. 73

F.1.2 Rayleigh integral projection example .............................................. 77

F.2 Other propagation method applications ............................................................ 81

Annex G (normative) Planar scanning of a hydrophone to determine acoustic output

power ............................................................................................................................ 82

G.1 Introduction ...................................................................................................... 82

G.2 General principle.............................................................................................. 82

G.3 Hydrophone scanning methodology .................................................................. 83

G.3.1 General methodology ...................................................................... 83

G.3.2 Particular considerations for implementation for HITU fields ........... 84

G.4 Corrections and sources of measurement uncertainty ...................................... 84

G.4.1 Uncertainty in the hydrophone calibration ...................................... 84

G.4.2 Planar scanning ............................................................................. 84

G.4.3 Attenuation factor of water: unfocusing transducers ...................... 85

G.4.4 Attenuation factor of water: focusing transducers .......................... 85

G.4.5 Received hydrophone signal ........................................................... 85

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– 4 – IEC TS 62556:2014 © IEC 2014

G.4.6 Integration ...................................................................................... 86

G.4.7 Finite size of the hydrophone .......................................................... 86

G.4.8 partial extent of integration ............................................................. 86

G.4.9 Non-linear propagation ................................................................... 86

G.4.10 Directional response ....................................................................... 87

G.4.11 Noise .............................................................................................. 87

G.4.12 Intensity approximated by derived intensity ..................................... 87

Annex H (informative) Properties of water ............................................................................ 88

H.1 General ............................................................................................................ 88

H.2 Attenuation coefficient for propagation in water ................................................ 89

Annex I (informative) Propagation medium and degassing ................................................... 90

Bibliography .......................................................................................................................... 91

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

a rectangular HITU transducer .............................................................................................. 47

Figure 2 – Schematic diagram of the different planes and lines in an ultrasonic field for

a circularly symmetric HITU transducer ................................................................................. 48

Figure 3 – Schematic diagram of the different planes and lines in an ultrasonic field for

a circularly symmetric HITU transducer with a circular hole in its center................................ 49

Figure 4 – Schematic diagram of the different planes and lines in an ultrasonic field for

a circularly symmetric HITU transducer with a rectangular hole in its center for a

diagnostic transducer (HITU transducer azimuth axis aligned with azimuth scan axis of

diagnostic transducer) .......................................................................................................... 50

Figure 5 – Parameters for describing a focusing transducer of an unknown geometry

(IEC 61828) .......................................................................................................................... 51

Figure 6 – Overall measurement scheme .............................................................................. 52

Figure C.1 – Schematic diagram of the ultrasonic transducer and hydrophone degrees

of freedom. X, Y and Z denote the axis directions relative to the mounted hydrophone

and ultrasonic transducer. ..................................................................................................... 59

Figure E.1 – Geometry of problem for forward and backward projection techniques. ............. 63

Figure E.2 – Transducer focused at –15mm, y = 48,16 mm, z = 56,85 mm ............................ 66

Figure E.3 – Selection of acquisition window ........................................................................ 70

Figure E.4 – Scanned field compared to its reconstruction from a finite window .................... 71

Figure F.1 – Transducer inside 2-axis scanner setup ............................................................ 73

Figure F.2 – Pressure amplitude as scanned ........................................................................ 74

Figure F.3 – Reconstructed pressure amplitude distribution in 3 orthogonal planes that

contain the focal point ........................................................................................................... 75

Figure F.4 – 3D representation of the focal beam for nominal focus at x = –0,85 mm,

y = –0,25 mm, z = 58,95 mm ................................................................................................. 76

Figure F.5 – Reconstruction of pressure amplitudes on the transducer surface

(transducer aperture plane)................................................................................................... 77

Figure F.6 – Experimental arrangement ................................................................................ 78

Figure F.7 – Amplitude and phase distribution of acoustic pressure measured at the

scanning region .................................................................................................................... 79

Figure F.8 – Amplitude and phase distribution of acoustic pressure reconstructed at

the transducer aperture plane ............................................................................................... 79

Figure F.9 – Comparison of the axial distribution of pressure amplitudes as projected

from the aperture plane (red) and as measured (blue) .......................................................... 80

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IEC TS 62556:2014 © IEC 2014 – 5 –
Figure F.10 –Comparison of the schlieren image (A) and the corresponding YZ

distribution of acoustic pressure amplitudes projected from the transducer aperture

plane (B) ............................................................................................................................... 81

Table H.1 – Speed of sound c [, ] and characteristic acoustic impedance, ρ c, as a

function of temperature, for propagation in water .................................................................. 88

---------------------- Page: 7 ----------------------
– 6 – IEC TS 62556:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – FIELD CHARACTERIZATION – SPECIFICATION
AND MEASUREMENT OF FIELD PARAMETERS FOR HIGH INTENSITY
THERAPEUTIC ULTRASOUND (HITU) TRANSDUCERS AND SYSTEMS
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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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.

The main task of IEC technical committees is to prepare International Standards. In

exceptional circumstances, a technical committee may propose the publication of a technical

specification when

• the required support cannot be obtained for the publication of an International Standard,

despite repeated efforts, or

• the subject is still under technical development or where, for any other reason, there is the

future but no immediate possibility of an agreement on an International Standard.

Technical specifications are subject to review within three years of publication to decide

whether they can be transformed into International Standards.

IEC/TS 62556, which is a technical specification, has been prepared by IEC technical

committee 87: Ultrasonics
---------------------- Page: 8 ----------------------
IEC TS 62556:2014 © IEC 2014 – 7 –
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
87/521/DTS 87/545/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.

NOTE 1 The following point types are used:
– Requirements: in roman type
– Notes: small roman type
– Words in bold in the text are defined in Clause 3
– Symbols and formulae: in Times New Roman + Italic.

NOTE 2 There are some inconsistencies in font type for symbols and formulae between some of the normative

references and this technical specification. They will be resolved in a future revision of the normative references.

The committee has decided that the contents of this 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
− transformed into an International standard,
− reconfirmed,
− withdrawn,
− replaced by a revised edition, or
− amended.
A bilingual version of this publication may be issued at a later date.

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: 9 ----------------------
– 8 – IEC TS 62556:2014 © IEC 2014
INTRODUCTION

The use of high intensity therapeutic ultrasound (HITU) has advanced to the point where

systems have achieved clinical approval for general use in numerous countries. Medical

applications and product development are continuing rapidly. Fast development in preclinical

medicine, clinical medicine, and product manufacture has created an urgent need to

standardize measurements of the basic acoustic parameters and the field characteristics of

HITU. In order to promote the further development of HITU and to ensure its safe and

effective use, common technical Specifications are required.

This technical specification is relevant to the measurement and specification of ultrasound

fields intended for medical therapeutic purposes. It addresses the requirements for high

intensity therapeutic ultrasound (HITU) fields, including those generally referred to as high

intensity focused ultrasound (HIFU). Lithotripsy and physiotherapy are excluded, since

there are existing International Standards for these applications.

As described in Annex A, because measurement at full output power from HITU systems still

presents technical challenges, this standard specifies measurement methods at relatively low

output levels and methodology for extrapolating these to higher therapeutic level fields.

---------------------- Page: 10 ----------------------
IEC TS 62556:2014 © IEC 2014 – 9 –
ULTRASONICS – FIELD CHARACTERIZATION – SPECIFICATION
AND MEASUREMENT OF FIELD PARAMETERS FOR HIGH INTENSITY
THERAPEUTIC ULTRASOUND (HITU) TRANSDUCERS AND SYSTEMS
1 Scope

This technical specification is applicable to high intensity therapeutic ultrasound (HITU)

devices, specifying:
– relevant parameters for quantifying the field;

– measurement methods at relatively low output levels and methodology for extrapolating

these to higher therapeutic level fields;
– consideration of sidelobes and pre-focal maxima;

– parameters relevant to HITU transducers of different construction and geometry, including

non-focusing, focusing with or without lenses, collimated, diverging and convergent

transducers, multi-element transducers, scanning transducers and multiple sources.

This technical specification is intended to support the ultrasonic measurement requirements

given in IEC 60601-2-62.

These specifications would have use in quality assurance, safety testing, and the

standardization of communications regarding the clinical performance of HITU systems.

Where possible, this technical specification incorporates specifications from other related

standards.

This technical specification does not apply to the following types of devices, which are

covered by other standards:
– lithotripters (see IEC 61846);
– surgical equipment (see IEC 61847);
– physiotherapy devices (see IEC 61689).

Throughout this technical specification SI units are used. In the specification of certain

parameters, such as beam-areas and intensities, it may be convenient to use decimal

multiples or sub-multiples. For example, beam-area may be specified in cm and intensities in

2 2
W/cm or mW/cm .
2 Normative references

The 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 60050 (all parts), International Electrotechnical Vocabulary (available at
)

IEC 60601-2-62, Medical electrical equipment – Particular requirements for the basic safety

and essential performance of high intensity therapeutic ultrasound (HITU) equipment

IEC 61161, Ultrasonics – Power measurement – Radiation force balances and performance

requirements
---------------------- Page: 11 ----------------------
– 10 – IEC TS 62556:2014 © IEC 2014

IEC 61689, Ultrasonics – Physiotherapy systems – Field specifications and methods of

measurement in the frequency range 0,5 MHz to 5 MHz

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

for the
...

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