BS EN IEC 61828:2021

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Ultrasonics. Transducers. Definitions and measurement methods regarding focusing for the transmitted fields

Published By	Publication Date	Number of Pages
BSI	2021	118

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Categories: 17.140.50 - Electroacoustics, BSI

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Description

This document

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.

This document 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.

This document 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.

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PDF Pages	PDF Title
2	undefined
5	Annex ZA(normative)Normative references to international publicationswith their corresponding European publications
7	English CONTENTS
11	FOREWORD
13	INTRODUCTION
14	1 Scope 2 Normative references
15	3 Terms and definitions
46	4 Symbols
49	5 Independent measurement of total acoustic output power 6 Acoustic field measurement: equipment 6.1 Hydrophone 6.1.1 General 6.1.2 Sensitivity of a hydrophone
50	6.1.3 Directional response of a hydrophone 6.1.4 Effective hydrophone radius 6.1.5 Choice of the size of a hydrophone active element
51	6.1.6 Hydrophone pressure limits 6.1.7 Hydrophone intensity limits
52	6.1.8 Hydrophone cable length and amplifiers 6.2 Requirements for positioning and water baths 6.2.1 General 6.2.2 Positioning systems
53	6.2.3 Water bath
54	6.3 Requirements for data acquisition and analysis systems
55	6.4 Requirements and recommendations for ultrasonic equipment being characterized 7 Measurement procedure 7.1 General 7.2 Preparation and alignment 7.2.1 General drive and field conditions
56	7.2.2 Initial adjustment to driving voltage
57	7.2.3 Preparation of source transducer 7.2.4 Aligning an ultrasonic transducer and hydrophone
58	7.2.5 Finding the beam axis
60	7.2.6 Measurements to determine field level conditions
61	7.2.7 Determining if transducer is focusing
62	7.2.8 Measuring other beamwidth parameters of a focusing transducer
63	7.2.9 Measuring the beam area parameters
64	7.2.10 Measuring additional beam maximum based parameters
65	7.2.11 Alternative: calculation of focal parameters using numerical projection
66	7.2.12 Plane wave transmitted fields 7.2.13 Steered plane waves 7.2.14 Measurements of high intensity therapeutic ultrasound fields
67	7.2.15 Calculation of Isa
68	7.2.16 Further evaluation for sidelobes and pre-focal maxima
70	7.3 Considerations for scanning transducers and transducers with multiple sources 7.3.1 Automatic scanning transducers 7.4 Spatial impulse response and beamplots 7.4.1 General
71	7.4.2 Point target 7.4.3 Beamplots and beam contour plots 7.5 Plane wave compounding
72	Annex A (informative)Background for the transmission/ Characteristics of focusing transducers A.1 General
73	A.2 Field of piston source A.3 Focusing with a lens
76	A.4 Focusing with a concave transducer
78	A.5 Geometric focusing gains
79	A.6 Beamwidth estimation
81	Figures Figure A.1 – Beam contour plot: contours at −6 dB, −12 dB, and −20 dBfor a 5 MHz transducer with a radius of curvature of D = 50 mmcentred at location 0,0 (bottom centre of graph) Figure A.2 – Types of geometric focusing
82	Figure A.3 – Transducer options
83	Figure A.4 – Parameters for describing a focusing transducer of known geometry Figure A.5 – Path difference parameters for describinga focusing transducer of known geometry
84	Annex B (informative)Rationale for focusing and nonfocusing definitions B.1 Overview B.1.1 Background information B.1.2 General B.1.3 Focusing transducers
85	B.1.4 Focusing methods
86	B.1.5 Known and unknown focusing transducers B.1.6 Focusing and beamwidth
87	B.1.7 Focusing parameter definitions B.1.8 Applications of focusing definitions B.1.9 Relation of present definitions to physiotherapy transducers (treatment heads) B.1.10 Relation of present definitions to therapeutic transducers
88	B.2 System and measurement requirements B.2.1 General B.2.2 Transmitted pressure waveforms B.2.3 Transmitted fields B.2.4 The scan plane and the steering of beams
89	B.2.5 Pulse echo field measurements Figure B.1 – Electronic focusing along z by transmit beamforming in the scan plane xz
90	Figure B.2 – Field parameters for a nonfocusing transducer of known geometry.For example, for a circularly symmetric geometry,transducers have a diameter 2a and a beam axis along z Figure B.3 – Phased array geometry and construction for electronic focusing in the azimuth plane and mechanical lens focusing in the elevation plane
91	Figure B.4 – Field parameters for a focusing transducer of known geometry Figure B.5 – Definitions for pressure-based field measurementsfor an unknown transducer geometry
92	Figure B.6 – Beamwidth focus for transducers of known and unknown geometry
93	Figure B.7 – Beam maximum parameters Figure B.8 – Pressure focus for a transducer of known geometry (design case)
94	Figure B.9 – Pressure focus for a transducer of unknown geometry (measurement case) Figure B.10 – Beam area parameters
95	Figure B.11 – Beam axis parameters: pulse-pressure-squared-integral level relative to the beam maximum in decibels (dB) plotted against axial distance
96	Figure B.12 – Beamplot parameters
97	Figure B.13 – Schematic diagram of the different planes and linesin an ultrasonic field for a rectangular transducer
98	Figure B.14 – Schematic diagram of the different planes andlines in an ultrasonic field for a circular transducer
99	Annex C (informative)Methods for determining the beam axis for well-behaved beams C.1 Comparisons of beam axis search methods Tables Table C.1 – Standard deviations for x and y scans usingthree methods of determining the centre of the beam
100	C.2 Beamwidth midpoint method Figure C.1 – x-axis scan at 9 cm depth for the first focal zone with beam centre Figure C.2 – x-axis scan at 4,4 cm depth for the second focal zone
101	Table C.2 – Decibel beamwidth levels for determining midpoints
102	Annex D (informative)Methods for determining the beam axisfor beams that are not well behaved
103	Figure D.1 – Asymmetric beam showing relative acoustic pressure versus sample number for the beamwidth midpoint method
104	Annex E (informative)Uncertainties E.1 General E.2 Overall (expanded) uncertainty E.3 Common sources of uncertainty
106	Annex F (informative)Transducer and hydrophone positioning systems Figure F.1 – Schematic diagram of the ultrasonic transducer andhydrophone degrees of freedom
107	Annex G (informative)Planar scanning of a hydrophone to determine acoustic output power G.1 Overview G.2 General principle
108	G.3 Hydrophone scanning methodology G.3.1 General methodology
109	G.3.2 Particular considerations for implementation for HITU fields G.4 Corrections and sources of measurement uncertainty G.4.1 Uncertainty in the hydrophone calibration G.4.2 Planar scanning G.4.3 Attenuation factor of water: unfocusing transducers
110	G.4.4 Attenuation factor of water: focusing transducers G.4.5 Received hydrophone signal G.4.6 Integration
111	G.4.7 Finite size of the hydrophone G.4.8 Partial extent of integration G.4.9 Non-linear propagation G.4.10 Directional response
112	G.4.11 Noise G.4.12 Intensity approximated by derived intensity
113	Annex H (informative)Properties of water H.1 General Table H.1 – Speed of sound, c, and characteristic acoustic impedance, ρ c,as a function of temperature, for propagation in water
114	H.2 Attenuation coefficient for propagation in water
115	Bibliography

Additional information

Status	Definitive
Pages	118
Publication Date	2021-02-10
ISBN	978 0 580 90717 3
Standard Number	BS EN IEC 61828:2021
Title	Ultrasonics. Transducers. Definitions and measurement methods regarding focusing for the transmitted fields
Identical National Standard Of	EN 61828, IEC 61828
Replaces	BS EN 61828:2002
Descriptors	Clinical investigation instruments, Transducers, Wave properties and phenomena, Ultrasonic frequencies, Electrical medical equipment, Ultrasonic medical apparatus, Focusing, Transmittance, Ultrasonic devices, Radiology apparatus (medical), Medical equipment, Ultrasonics
Publisher	BSI
Committee	EPL/87
ICS Codes	17.140.50 - Electroacoustics

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