WG 6 - TC 87/WG 6

IEC 61828:2020
- provides definitions for the transmitted field characteristics of focusing and nonfocusing transducers for applications in medical ultrasound;
- relates these definitions to theoretical descriptions, design, and measurement of the transmitted fields of focusing transducers;
- gives measurement methods for obtaining defined field characteristics of focusing and nonfocusing transducers;
- specifies beam axis alignment methods appropriate for focusing and nonfocusing transducers.
IEC 61828:2021 relates to focusing ultrasonic transducers operating in the frequency range appropriate to medical ultrasound (0,5 MHz to 40 MHz) for both therapeutic and diagnostic applications. It shows how the characteristics of the transmitted field of transducers can be described from the point of view of design, as well as measured by someone with no prior knowledge of the construction details of a particular device. The transmitted ultrasound field for a specified excitation is measured by a hydrophone in either a standard test medium (for example, water) or in a given medium. This document applies only to media where the field behaviour is essentially like that in a fluid (i.e. where the influence of shear waves and elastic anisotropy is small), including soft tissues and tissue-mimicking gels. Any aspects of the field that affect their theoretical description or are important in design are also included. These definitions would have use in scientific communications, system design and description of the performance and safety of systems using these devices.
IEC 61828:2021 incorporates definitions from other related standards where possible, and supplies more specific terminology, both for defining focusing characteristics and for providing a basis for measurement of these characteristics.
IEC 61828:2021 cancels and replaces the first edition published in 2001. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) Clause 6 on Measurement procedures has been replaced by Clause 6: "Acoustic field measurement: equipment" and Clause 7: "Measurement procedure" and related definitions.
b) Reorganization of definitions and measurement section to accommodate specific sets of measurements for focusing, nonlinearity, beam axis alignment, beam area, beam maximum, numerical projection, plane wave, high intensity therapeutic ultrasound, multiple sources, spatial impulse response and compound plane waves. Clause 3 has been moved to Annex B.
c) The normative references have been updated and the Bibliography has been expanded from 8 to 40 references.
d) Twelve figures have been updated and seven new figures (B.1, B.3, B.7, B.10, B.11, B.12, B.13, B.14) have been added to facilitate measurements and be consistent with measurement terminology.
e) New measurements have been added for time delays, arrays, plane waves and spatial impulse response.
f) Annex A has been expanded to provide general guidance on pulsed waves, system responses, focusing gains and minimum beamwidth estimation.
g) New annexes have been added:
• Annex B (informative) Rationale for focusing and nonfocusing definitions
• Annex E (informative) Uncertainties;
• Annex F (informative) Transducer and hydrophone positioning systems;
• Annex G (informative) Planar scanning of a hydrophone to determine acoustic output power;
• Annex H (informative) Properties of water;
In addition, Annex A was reorganized and new Clauses A.1, A.5 and A.6 were added.
h) Guidelines for remaining within the manufacturer’s pressure and intensity hydrophone limits and the determination of the extent of nonlinearity in the field have been added.

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).

IEC 62555:2013 establishes general principles relevant to HITU fields for the use of radiation force balances in which an obstacle (target) intercepts the sound field to be measured; specifies a calorimetric method of determining the total emitted acoustic power of ultrasonic transducers based on the measurement of thermal expansion of a fluid-filled target; specifies requirements related to the statement of electrical power characteristics of ultrasonic transducers; provides guidance related to the avoidance of acoustic cavitation during measurement; provides guidance related to the measurement of HITU transducers of different construction and geometry, including collimated, diverging and convergent transducers, and multi-element transducers; provides guidance on the choice of the most appropriate measurement method; and provides information on assessment of overall measurement uncertainties. This International Standard is applicable to the measurement of ultrasonic power generated by HITU equipment up to 500 W in the frequency range from 0,5 MHz to 5 MHz. HITU equipment may generate convergent, collimated or divergent fields. For frequencies less than 500 kHz, no validations exist and the user should assess the uncertainties of the power measurement and measurement system at the frequencies of operation. This International Standard does not apply to ultrasound equipment used for physiotherapy, for lithotripsy for general pain relief.

IEC/TR 62649:2010(E) is relevant to the measurement and specification of ultrasound fields intended for medical therapeutic purposes. Lithotripsy and physiotherapy are excluded, since there are existing International Standards for these applications. IEC/TR 62649:2010 establishes:
- topics where there is a consensus that the development of International Standards would benefit the industries and/or patients;
- topics where the writing of standards should start immediately;
- topics where the writing of technical specifications should start immediately in order to gain practical experience and establish consensus prior to standardisation;
- topics which require future standardisation but where further research is required before initiating the writing of standards or technical specifications. IEC/TR 62649:2010 addresses primarily the requirements for measurement standards related to high intensity therapeutic ultrasound (HITU) [also known as high intensity focused ultrasound (HIFU)] fields which are both high intensity and focused and where the main mechanism for action is thermal. However, aspects of the discussion, conclusions and any resulting standards or technical specifications may also be relevant to therapeutic applications which are either focused or high intensity or where the main mechanism is not thermal. Scientific literature has been reviewed and responses to a questionnaire which was sent to experts around the world are reported.

This International Standard - provides definitions for the transmitted field characteristics of focusing transducers for applications in medical ultrasound; - relates these definitions to theoretical descriptions, design, and measurement of the transmitted fields of focusing transducers; - gives measurement methods for obtaining defined characteristics of focusing transducers; - specifies beam axis alignment methods appropriate for focusing transducers. This International Standard relates to focusing ultrasonic transducers operating in the frequency range appropriate to medical ultrasound (0,5 MHz to 40 MHz) for both therapeutic and diagnostic applications. It shows how the characteristics of the transmitted field of transducers may be described from the point of view of design, as well as measured by someone with no prior knowledge of the construction details of a particular device. The radiated ultrasound field for a specified excitation is measured by a hydrophone in either a standard test medium (for example, water) or in a given medium. The standard applies only to media where the field behaviour is essentially like that in a fluid (i.e. where the influence of shear waves and elastic anisotropy is small), including soft tissues and tissue-mimicking gels. Any aspects of the field that affect their theoretical description or are important in design are also included. These definitions would have use in scientific communications, system design and description of the performance and safety of systems using these devices.