SIST EN 61157:2008
(Main)Standard means for the reporting of the acoustic output of medical diagnostic ultrasonic equipment
Standard means for the reporting of the acoustic output of medical diagnostic ultrasonic equipment
This International Standard is applicable to medical diagnostic ultrasonic equipment.
– It provides a set of traceable acoustic parameters describing the acoustic fields.
– It defines a standard means and format for the reporting of the acoustic output information.
– It also describes a reduced dataset recommended for equipment generating low acoustic output levels.
NOTE The information tabulated in this standard format can be used for
a) exposure planning for biological effects studies;
b) exposure data for prospective epidemiological studies conducted using exposure conditions similar to those reported in this standard. In the absence of actual exposure data for retrospective epidemiological studies, the information tabulated in this standard format might also be used with
cautionary comment.
Normverfahren für die Angabe der akustischen Ausgangsgrößen von medizinischen Ultraschalldiagnostikgeräten
Moyens normalisés pour la déclaration des émissions acoustiques des appareils de diagnostic médical à ultrasons
Définit les critères pour la déclaration des informations intéressant les émissions acoustiques: 1. à présenter dans des bordereaux de données techniques fournis par les fabricants aux acheteurs éventuels des appareils; 2. à déclarer dans la documentation/le manuel d'accompagnement fournis par les fabricants; 3. sous la forme d'informations de fond devant être présentées, sur demande, aux parties intéressées par les fabricants.
Standardni načini poročanja o akustičnem izhodu medicinske ultrazvočne diagnostične opreme (IEC 61157:2007)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 61157:2008
01-februar-2008
1DGRPHãþD
SIST EN 61157:2002
6WDQGDUGQLQDþLQLSRURþDQMDRDNXVWLþQHPL]KRGXPHGLFLQVNHXOWUD]YRþQH
GLDJQRVWLþQHRSUHPH ,(&
Standard means for the reporting of the acoustic output of medical diagnostic ultrasonic
equipment
Normverfahren für die Angabe der akustischen Ausgangsgrößen von medizinischen
Ultraschalldiagnostikgeräten
Moyens normalisés pour la déclaration des émissions acoustiques des appareils de
diagnostic médical à ultrasons
Ta slovenski standard je istoveten z: EN 61157:2007
ICS:
11.040.50 Radiografska oprema Radiographic equipment
11.040.55 'LDJQRVWLþQDRSUHPD Diagnostic equipment
17.140.50 Elektroakustika Electroacoustics
SIST EN 61157:2008 en,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 61157:2008
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SIST EN 61157:2008
EUROPEAN STANDARD
EN 61157
NORME EUROPÉENNE
November 2007
EUROPÄISCHE NORM
ICS 11.040.50; 11.140.50 Supersedes EN 61157:1994
English version
Standard means for the reporting of the acoustic output
of medical diagnostic ultrasonic equipment
(IEC 61157:2007)
Moyens normalisés pour la déclaration Normverfahren für die Angabe
des émissions acoustiques des appareils der akustischen Ausgangsgrößen
de diagnostic médical à ultrasons von medizinischen
(CEI 61157:2007) Ultraschalldiagnostikgeräten
(IEC 61157:2007)
This European Standard was approved by CENELEC on 2007-10-01. 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, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
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
© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61157:2007 E
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SIST EN 61157:2008
EN 61157:2007 – 2 –
Foreword
The text of document 87/356/CDV, future edition 2 of IEC 61157, prepared by IEC TC 87, Ultrasonics,
was submitted to the IEC-CENELEC parallel Unique Acceptance Procedure and was approved by
CENELEC as EN 61157 on 2007-10-01.
This European Standard supersedes EN 61157:1994.
The changes with respect to EN 61157:1994 are listed below:
– maintenance on this standard and the referenced standards EN 61161 and EN 62127-1;
– a clause on compliance has been added.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2008-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2010-10-01
NOTE The following print types are used:
– Requirements: in roman type
– Test specifications: in italic type
– Notes: in small roman type
– Words in bold in the text are defined in Clause 3.
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61157:2007 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 61689 NOTE Harmonized as EN 61689:2007 (not modified).
IEC 61828 NOTE Harmonized as EN 61828:2001 (not modified).
__________
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SIST EN 61157:2008
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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 When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year
IEC 60050-801 1994 International Electrotechnical Vocabulary – –
(IEV) -
Chapter 801: Acoustics and electroacoustics
1) 2)
IEC 61161 – Ultrasonics - Power measurement - EN 61161 2007
Radiation force balances and performance
requirements
1) 2)
IEC 62127-1 – Ultrasonics - Hydrophones - EN 62127-1 2007
Part 1: Measurement and characterization of
medical ultrasonic fields up to 40 MHz
ISO 16269-6 2005 Statistical interpretation of data - – –
Part 6: Determination of statistical tolerance
intervals
ISO/IEC Guide 98 1995 Guide to the expression of uncertainty in – –
measurement (GUM)
1)
Undated reference.
2)
Valid edition at date of issue.
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SIST EN 61157:2008
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SIST EN 61157:2008
IEC 61157
Edition 2.0 2007-08
INTERNATIONAL
STANDARD
Standard means for the reporting of the acoustic output of medical diagnostic
ultrasonic equipment
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
V
ICS 11.040.50; 11.140.50 ISBN 2-8318-9257-0
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SIST EN 61157:2008
– 2 – 61157 © IEC:2007(E)
CONTENTS
FOREWORD.3
INTRODUCTION.5
1 Scope.6
2 Normative references .6
3 Terms, definitions and symbols .6
4 Requirements .16
4.1 General .16
4.2 Requirements for the reporting of acoustic output information .17
4.2.1 Technical data sheets information format .17
4.2.2 Detailed operating mode data sheets information format .18
4.2.3 Background information.19
4.2.4 Diagnostic fields in the absence of scan-frame synchronization.20
4.2.5 Dataset for low acoustic output equipment.20
5 Compliance statement .21
5.1 General .21
5.2 Maximum probable values .21
5.3 Sampling .21
6 Test methods .22
7 Presentation of results.22
Annex A (normative) Presentation of acoustic output information.23
Annex B (informative) Reporting requirements for extensive systems .25
Annex C (informative) Rationale .26
Index of defined terms .30
Bibliography.32
Figure C.1 – Schematic diagram showing the relationship between the various defined
surfaces and distances for a mechanical sector scanner with water stand-off
distance when applied to a patient.27
Figure C.2 – Schematic diagram showing the relationship between the various defined
parameters and distances for a mechanical sector scanner during the
measurement of acoustic output .27
Figure C.3 – Schematic diagram showing various defined parameters associated with
the distribution of the scan lines in a linear array scanner and mechanically-
scanned sector scanner.28
Figure C.4 – Schematic diagram illustrating the peak-rarefactional acoustic pressure
during an acoustic pulse.29
Table 1 – List of symbols .15
Table A.1 – An example of reporting of the acoustic output of a 3,5 MHz scan-head for
a phased-array sector scanner in accordance with this standard.24
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SIST EN 61157:2008
61157 © IEC:2007(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
STANDARD MEANS FOR THE REPORTING
OF THE ACOUSTIC OUTPUT OF MEDICAL DIAGNOSTIC
ULTRASONIC EQUIPMENT
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 recommendations 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 61157 has been prepared by IEC technical committee 87:
Ultrasonics.
This second edition cancels and replaces the first edition published in 1992. This edition
constitutes a minor revision.
The changes with respect to the previous edition are listed below:
• maintenance on this standard and the referenced standards IEC 61161 and IEC 62127-1.
• a clause on compliance has been added.
The text of this standard is based on the following documents:
Enquiry draft Report on voting
87/356/CDV 87/374/RVC
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SIST EN 61157:2008
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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.
NOTE The following print types are used:
– Requirements: in roman type
– Test specifications: in italic type
– Notes: in small roman type
– Words in bold in the text are defined in Clause 3.
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 publication may be issued at a later date.
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SIST EN 61157:2008
61157 © IEC:2007(E) – 5 –
INTRODUCTION
This International Standard specifies a standard means and format for the reporting of the
acoustic output of medical diagnostic ultrasonic equipment. The numerical values for reporting
purposes represent the average values for the maximum output conditions for a given
discrete- or combined-operating mode and are derived from measurements made in water.
Intensity parameters are specified in this standard, but these are regarded as derived
quantities that are meaningful only under certain assumptions related to the ultrasonic field
being measured.
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STANDARD MEANS FOR THE REPORTING
OF THE ACOUSTIC OUTPUT OF MEDICAL DIAGNOSTIC
ULTRASONIC EQUIPMENT
1 Scope
This International Standard is applicable to medical diagnostic ultrasonic equipment.
– It provides a set of traceable acoustic parameters describing the acoustic fields.
– It defines a standard means and format for the reporting of the acoustic output information.
– It also describes a reduced dataset recommended for equipment generating low acoustic
output levels.
NOTE The information tabulated in this standard format can be used for
a) exposure planning for biological effects studies;
b) exposure data for prospective epidemiological studies conducted using exposure conditions similar
to those reported in this standard. In the absence of actual exposure data for retrospective
epidemiological studies, the information tabulated in this standard format might also be used with
cautionary comment.
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 60050-801:1994 International Electrotechnical Vocabulary – Chapter 801: Acoustics and
electroacoustics
IEC 61161, Ultrasonics – Power measurement – Radiation force balances and performance
requirements
IEC 62127-1, Ultrasonics – Hydrophones – Part 1: Measurement and characterization of
medical ultrasonic fields up to 40 MHz
ISO 16269-6:2005, Statistical interpretation of data – Part 6: Determination of statistical
tolerance intervals
ISO/IEC Guide 98:1995, Guide to the expression of uncertainty in measurement (GUM)
3 Terms, definitions and symbols
For the purposes of this document, the terms and definitions given in IEC 62127-1, IEC 61161,
the Index of defined terms at the end of this standard and the following definitions apply.
Figures C.1 to C.4 illustrate some of the defined parameters given below.
3.1
acoustic output freeze
condition of a system for which the acoustic output is disabled when there is no active
updating of ultrasonic echo information
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61157 © IEC:2007(E) – 7 –
3.2
acoustic pulse waveform
temporal waveform of the instantaneous acoustic pressure at a specified position in an
acoustic field and displayed over a period sufficiently long to include all significant acoustic
information in a single pulse or tone-burst, or in one or more cycles in a continuous wave
NOTE 1 Temporal waveform is a representation (e.g. oscilloscope presentation or equation) of the instantaneous
acoustic pressure.
NOTE 2 Definition adapted from IEC 60469-1.
3.3
acoustic repetition period
arp
pulse repetition period for non-automatic scanning systems and the scan repetition period
for automatic scanning systems, equal to the time interval between corresponding points of
consecutive cycles for continuous wave systems
NOTE 1 The acoustic repetition period is expressed in seconds (s).
[IEC 62127-1, definition 3.2]
3.4
acoustic frequency
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. Acoustic-working frequencies are defined in 3.4.1 and 3.4.2.
NOTE 2 In a number of cases, the present definition is not very helpful or convenient, especially for broadband
transducers. In that case, a full description of the frequency spectrum should be given in order to enable any
frequency-dependent correction to the signal.
NOTE 3 Acoustic frequency is expressed in hertz (Hz).
3.4.1
zero-crossing acoustic-working frequency
f
awf
this is determined according to the procedure specified in IEC/TR 60854
NOTE This frequency is intended for continuous wave systems only.
3.4.2
arithmetic-mean acoustic-working frequency
f
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
1
magnitude
NOTE 1 This frequency is intended for pulse-wave systems only.
NOTE 2 It is assumed that f < f
1 2
.
3.5
bandwidth
BW
difference in the most widely separated frequencies f and f at which the magnitude of the
1 2
acoustic pressure spectrum becomes 3 dB below the peak magnitude, at a specified point in
the acoustic field
NOTE Bandwidth is expressed in hertz (Hz).
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3.6
beam area
A
b
area in a specified plane perpendicular to the beam axis consisting of all points at which the
pulse-pressure-squared integral is greater than a specified fraction of the maximum value
of the pulse-pressure-squared integral in that plane
NOTE 1 If the position of the plane is not specified, it is the plane passing through the point corresponding to the
spatial-peak temporal-peak acoustic pressure in the whole acoustic field.
NOTE 2 In a number of cases, the term pulse-pressure-squared integral is replaced everywhere in the above
definition by any linearly related quantity, for example:
a) in the case of a continuous wave signal the term pulse-pressure-squared integral is replaced by mean
square acoustic pressure as defined in IEC 61689;
b) in cases where signal synchronisation with the scanframe is not available the term pulse-pressure-squared
integral may be replaced by temporal average intensity.
NOTE 3 Some specified levels are 0,25 and 0,01 for the −6 dB and −20 dB beam areas, respectively.
2
NOTE 4 Beam area is expressed in metres squared (m ).
3.7
beam axis
straight line that passes through the beam centrepoints of two planes perpendicular to the
line which connects the point of maximal pulse-pressure-squared integral with the centre of
the external transducer aperture
NOTE 1 The location of the first plane is the location of the plane containing the maximum pulse-pressure-
squared integral or, alternatively, is one containing a single main lobe which is in the focal Fraunhofer zone. The
location of the second plane is as far as is practicable from the first plane and parallel to the first with the same two
orthogonal scan lines (x and y axes) used for the first plane.
NOTE 2 In a number of cases, the term pulse-pressure-squared integral is replaced in the above definition by
any linearly related quantity, for example:
a) in the case of a continuous wave signal the term pulse-pressure-squared integral is replaced by mean square
acoustic pressure as defined in IEC 61689;
b) in cases where signal synchronisation with the scanframe is not available, the term pulse-pressure-squared
integral may be replaced by temporal average intensity.
[IEV 62127-1,definition 3.8 modified]
3.8
beam centrepoint
position determined by the intersection of two lines passing through the beamwidth
midpoints of two orthogonal planes, xz and yz
3.9
beamwidth midpoint
linear average of the location of the centres of beamwidths in a plane
NOTE The average is taken over as many beamwidth levels given in Table K.1 of IEC 62127-1 as signal level
permits).
3.10
beamwidth
w , w , w
6 12 20
greatest distance between two points on a specified axis perpendicular to the beam axis
where the pulse-pressure-squared integral falls below its maximum on the specified axis by
a specified amount
NOTE 1 In a number of cases, the term pulse-pressure-squared integral is replaced in the above definition by
any linearly related quantity, for example:
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SIST EN 61157:2008
61157 © IEC:2007(E) – 9 –
a) in the case of a continuous wave signal the term pulse-pressure-squared integral is replaced by mean
square acoustic pressure as defined in IEC 61689,
b) in cases where signal synchronisation with the scanframe is not available the term pulse-pressure-squared
integral may be replaced by temporal average intensity.
NOTE 2 Commonly used beamwidths are specified at –6 dB, –12 dB and –20 dB levels below the maximum. The
decibel calculation implies taking 10 times the logarithm of the ratios of the integrals.
NOTE 3 Beamwidth is expressed in metres (m).
3.11
central scan line
for automatic scanning systems, the ultrasonic scan line closest to the symmetry axis of the
scan plane
3.12
external transducer aperture
part of the surface of the ultrasonic transducer or ultrasonic transducer element group
assembly that emits ultrasonic radiation into the propagation medium
NOTE 1 This surface is either directly in contact with the patient or is in contact with a water or liquid path to the
patient (see IEC 62127-1, Figure 1).
[IEC 62127-1,definition 3.27 modified]
3.13
instantaneous acoustic pressure
p(t)
pressure minus the ambient pressure at a particular instant in time and at a particular point in
an acoustic field (see also IEV 801-21-19)
NOTE Instantaneous acoustic pressure is expressed in pascals (Pa).
3.14
instantaneous intensity
I(t)
acoustic energy transmitted per unit time in the direction of acoustic wave propagation per
unit area normal to this direction at a particular instant in time and at a particular point in an
acoustic field
NOTE 1 Instantaneous intensity is the product of instantaneous acoustic pressure and particle velocity. It is
difficult to measure intensity in the ultrasound frequency range. For the measurement purposes referred to in this
standard, and if it is reasonable to assume far field conditions, the instantaneous intensity, I is approximated as
2
p(t)
I(t) = (1)
ρ c
where
p(t) is the instantaneous acoustic pressure;
ρ is the density of the medium;
c is the velocity of sound in the medium.
2
NOTE 2 Instantaneous intensity is expressed in watts per metre squared (W/m ).
3.15
medical diagnostic ultrasonic equipment (or system)
combination of the ultrasound instrument console and the transducer assembly making up
a complete diagnostic system
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3.16
nominal frequency
the ultrasonic frequency of operation of an ultrasonic transducer or ultrasonic transducer
element group quoted by the designer or manufacturer
[IEC 60854, definition 3.7 modified]
3.17
operating mode
3.17.1
combined-operating mode
mode of operation of a system that combines more than one discrete-operating modes
NOTE Examples of combined-operating modes are real-time B-mode combined with M-mode (B+M), real-time
B-mode combined with pulsed Doppler (B+D), colour M-mode (cM), real-time B-mode combined with M-mode and
pulsed Doppler (B+M+D), real-time B-mode combined with real-time flow-mapping Doppler (B+rD), i.e. flow-
mapping in which different types of acoustic pulses are used to generate the Doppler information and the imaging
information.
[IEC 62127-1, definition 3.39.1]
3.17.2
discrete-operating mode
mode of operation of medical diagnostic ultrasonic equipment in which the purpose of the
excitation of the ultrasonic transducer or ultrasonic transducer element group is to utilize only
one diagnostic methodology
NOTE 1 Examples of discrete-operating modes are A-mode (A), M-mode (M), static B-mode (sB), real-time B-
mode (B), continuous wave Doppler (cwD), pulsed Doppler (D), static flow-mapping (sD) and real-time flow-
mapping Doppler (rD) using only one type of acoustic pulse.
[IEC 62127-1, definition 3.39.2]
3.17.3
inclusive mode
combined-operating mode having acoustic output levels (p and I ) less than those
r spta
corresponding to a specified discrete-operating mode
[IEC 62127-1, definition 3.39.3]
3.17.4
non-scanning mode
mode of operation of a system that involves a sequence of ultrasonic pulses which give rise
to ultrasonic scan lines that follow the same acoustic path
[IEC 62127-1, definition 3.39.4]
3.17.5
scanning mode
mode of operation of a system that involves a sequence of ultrasonic pulses which give rise
to ultrasonic scan lines that do not follow the same acoustic path
NOTE The sequence of pulses is not necessarily made up of identical pulses. For instance, the use of sequential
multiple focal-zones is considered a scanning mode.
[IEC 62127-1, definition 3.39.5]
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61157 © IEC:2007(E) – 11 –
3.18
output beam area
A
ob
area of the ultrasonic beam derived from the −12 dB beam area at the external transducer
aperture
NOTE 1 For reasons of measurement accuracy, the –12 dB output beam area may 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, this area can be taken as the geometrical area of the ultrasonic transducer or
ultrasonic transducer element group.
2
NOTE 3 The output beam area is expressed in metres squared (m ).
[IEC 62127-1, definition 3.40]
3.19
output beam dimensions
X , Y
ob ob
dimensions of the ultrasonic beam (–12 dB beamwidth) in specified directions perpendicular
to eac
...
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