SIST EN 61266:2002
(Main)Ultrasonics - Hand-held probe Doppler foetal heartbeat detectors - Performance requirements and methods of measurement and reporting
Ultrasonics - Hand-held probe Doppler foetal heartbeat detectors - Performance requirements and methods of measurement and reporting
Is applicable to ultrasonic Doppler foetal heartbeat detectors which generate a single ultrasound beam and consist of a hand-held probe which is applied to the maternal abdomen to obtain information on foetal heart activity by means of the Doppler method using continuous wave (c.w) or quasi-continuous wave ultrasound. Establishes - methods of measurement of performances - requirements for the performance and the - reporting of performance
Ultraschall - Handgehaltene Doppler-Herzschlagdetektoren für Föten - Leistungsanforderungen sowie Meß- und Angabeverfahren
Ultrasons - Détecteurs des battements de coeur foetal à effet Doppler avec sonde à main - Prescriptions de performance et méthodes de mesure et de signalement
S'applique aux détecteurs ultrasonores des battements de coeur foetal par effet Doppler qui produisent un faisceau ultrasonore unique et qui consistent en une sonde à main appliquée sur l'abdomen maternel pour recueillir des informations sur l'activité du coeur foetal au moyen de la méthode Doppler utilisant des ultrasons à onde entretenue ou quasi-entretenue. Etablit: - des méthodes de mesure des performances - des prescriptions de performance et pour le signalement de ces performances
Ultrasonics - Hand-held probe Doppler foetal heartbeat detectors - Performance requirements and methods of measurement and reporting (IEC 61266:1994)
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 61266:2002
01-september-2002
Ultrasonics - Hand-held probe Doppler foetal heartbeat detectors - Performance
requirements and methods of measurement and reporting (IEC 61266:1994)
Ultrasonics - Hand-held probe Doppler foetal heartbeat detectors - Performance
requirements and methods of measurement and reporting
Ultraschall - Handgehaltene Doppler-Herzschlagdetektoren für Föten -
Leistungsanforderungen sowie Meß- und Angabeverfahren
Ultrasons - Détecteurs des battements de coeur foetal à effet Doppler avec sonde à
main - Prescriptions de performance et méthodes de mesure et de signalement
Ta slovenski standard je istoveten z: EN 61266:1995
ICS:
11.040.50 Radiografska oprema Radiographic equipment
11.040.55 'LDJQRVWLþQDRSUHPD Diagnostic equipment
17.140.50 Elektroakustika Electroacoustics
SIST EN 61266:2002 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 61266:2002
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SIST EN 61266:2002
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SIST EN 61266:2002
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SIST EN 61266:2002
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SIST EN 61266:2002
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SIST EN 61266:2002
NORME CEI
IEC
INTERNATIONALE
1266
INTERNATIONAL
Première édition
STANDARD
First edition
1994-12
Ultrasons –
Détecteurs des battements de coeur foetal
à effet Doppler avec sonde à main –
Prescriptions de performance et méthodes
de mesure et de signalement
Ultrasonics –
Hand-held probe Doppler foetal heartbeat
–
detectors
requirements and methods of
Performance
measurement and reporting
Droits de reproduction réservés — Copyright — all rights reserved
© CEI 1994
cette publication ne peut être reproduite ni rt of this publication may be reproduced or utilized in
Aucune partie de No pa
et par
utilisée sous quelque forme que ce soit aucun pro- any form or by any means, electronic or mechanical,
compris la photocopie et cédé, électronique ou mécanique, y including photocopying and microfilm, without permission
microfilms, sans l'accord écrit de l'éditeur. in writing from the publisher.
les
Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembé Genève, Suisse
Commission Electrotechnique Internationale CODE PRIX
International Electrotechnical Commission
PRICE CODE U
IEC MentayHapoAHaa 3neurporexuUVecnaa HOMHCCHR
Pour prix, voir catalogue en vigueur
•
For price, see current catalogue
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SIST EN 61266:2002
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1266©IEC:1994
CONTENTS
Page
FOREWORD 5
INTRODUCTION 7
Clause
1 Scope 9
2 Normative references 9
11
3 Definitions
4 List of symbols 15
15
5 Configuration
17
rformance 6 Pe
17
6.1 Acoustic working frequency
17
7 Safety
17
8 Tests
17
8.1 Acoustic working frequency
17
8.2 Output power
19
8.3 Spatial-peak temporal-peak acoustic pressure
19
8.4 Effective area of the ultrasonic transducer active element
19
8.5 Overall sensitivity
rformance of existing equipment 25
9 Preferred method for reporting pe
10 Specifications for labelling 27
11 Sampling 29
31
Figures
Annexes
Choice of target and determination of target plane-wave reflection loss 35
A
49
B Typical test equipment and test procedures
55
Determination of the two-way insertion loss of acoustic attenuators C
D Rationale 59
60
E Bibliography
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SIST EN 61266:2002
1266 ©IEC:1994 - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
ULTRASONICS - HAND-HELD PROBE DOPPLER FOETAL
HEARTBEAT DETECTORS -
PERFORMANCE REQUIREMENTS AND METHODS OF
MEASUREMENT AND REPORTING
FOREWORD
The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
1)
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
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. The 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 the IEC on technical matters, prepared by technical committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
They have the form of recommendations for international use published in the form of standards, technical
3)
reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
International Standard IEC 1266 has been prepared by IEC technical committee 87:
Ultrasonics.
The text of this standard is based on the following documents:
Report on voting
DIS
87/71/RVD
87(CO)34
Full information on the voting for the approval of this standard can be found in the report
on voting indicated in the above table.
All annexes are for information only.
In this standard the following print types are used:
- Requirements proper: in roman type.
- Test specifications: in italic type.
– Notes: in smaller roman type.
- Words in bold in the text are defined in clause 3.
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SIST EN 61266:2002
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1266 ©IEC:1994
INTRODUCTION
Hand-held ultrasonic Doppler foetal heartbeat detectors are widely used for monitoring
2 MHz,
foetal heartbeat during pregnancy. They normally operate at frequencies of circa
and consist of an ultrasonic transducer acoustically coupled to the maternal abdomen and
associated electronics. A beam of ultrasound is directed by the operator to impinge on the
foetal heart and a small fraction of the incident ultrasound is reflected from the moving
aces of the heart. This ultrasound is subject to a frequency shift as a result of the
su rf
Doppler effect. It is then detected by a receiving transducer. Signal processing separates
the low-frequency signals associated with the foetal heartbeat from the high-frequency
ultrasonic oscillations and amplifies them for audio detection.
This International Standard, IEC 1266, specifies methods of evaluating the performance of
ultrasonic foetal heartbeat detectors and, in particular, specifies a method of determining
the sensitivity of the system to the detection of a moving target.
Foetal Doppler monitoring devices use a flat probe strapped to the patient and work on a
principle similar to that of hand-held foetal heartbeat detectors but are not covered by this
standard. The reason is that monitoring devices require a wide angle of view which is
often realised by using a multi-element transducer. This makes the method of operation of
foetal Doppler monitors much more complex than that of hand-held foetal heartbeat detec-
tors which use a narrow beam. Methods of assessment of performance would also be
more complex.
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SIST EN 61266:2002
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1266 ©IEC:1994
ULTRASONICS - HAND-HELD PROBE DOPPLER FOETAL
HEARTBEAT DETECTORS -
PERFORMANCE REQUIREMENTS AND METHODS OF
MEASUREMENT AND REPORTING
1 Scope
This International Standard IEC 1266 establishes:
- methods of measurement of performance of a complete ultrasonic hand-held Dop-
pler foetal heartbeat detector (hereinafter referred to as "equipment");
- equipment;
requirements for the performance of
- requirements for the reporting of the performance of existing equipment;
- requirements for the declaration by manufacturers in accompanying literature of
aspects of the performance of equipment.
This International Standard is applicable to ultrasonic Doppler foetal heartbeat detectors
which generate a single ultrasound beam and consist of a hand-held probe which is
applied to the maternal abdomen to obtain information on foetal heart activity by means of
the Doppler method using continuous wave (c.w.) or quasi-continuous wave ultrasound.
This standard, however, currently does not cover the continuous monitoring devices which
generate more than one ultrasound beam and are usually of the type utilising a similar
principle of operation but using a flat probe strapped to the patient.
This International Standard is not an equipment design standard.
2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this International Standard. At the time of publication, the
editions indicated were valid. All normative documents are subject to revision, and parties
to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated
below. Members of IEC and ISO maintain registers of currently valid International
Standards.
IEC 601-1: 1988, Medical electrical equipment - Part 1: General requirements for safety
IEC 854: 1986,
Methods of measuring the performance of ultrasonic pulse-echo diagnostic
equipment
IEC 866: 1987, Characteristics and calibration of hydrophones for operation in the
frequency range 0,5 MHz to 15 MHz
IEC 1101: 1991, The absolute calibration of hydrophones using the planar scanning
technique in the frequency range 0,5 MHz to 15 MHz
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1266 ©IEC:1994
IEC 1102: 1991, Measurement and characterisation of ultrasonic fields using hydrophones
in the frequency range of 0,5 MHz to 15 MHz
IEC 1157: 1992, Requirements for the declaration of the acoustic output of medical
diagnostic ultrasonic equipment
IEC 1161: 1992, Ultrasonic power measurement in liquids in the frequency range 0,5 MHz
to 25 MHz
3 Definitions
For the purposes of this International Standard, the following definitions apply:
3.1 acoustic coupling medium: Material placed between the probe and the body
ace in order to maintain acoustic transmission.
su rf
3.2 acoustic working frequency: Frequency of an acoustic signal based on the obser-
vation of the output of a hydrophone placed in an acoustic field.
For the purposes of this International standard, the signal is analysed using the
zero-crossing frequency technique, see IEC 854.
[3.4.1 of 1EC 1102].
3.3 continuous wave ultrasound: Ultrasonic oscillations which are either continuous or
quasi-continuous lasting for many tens of cycles.
3.4 Doppler frequency: Change in frequency of an ultrasound scattered wave caused
by relative motion between the scatterer and the probe. It is the difference frequency
between the transmitted and the received wave.
effective area of the ultrasonic transducer active element: -6 dB beam area at a
3.5
distance of 5 mm from the face of the probe.
[3.6 of IEC 1102].
Unit: millimetre squared, mm2
3.6 Doppler signal: Signal at the Doppler frequency.
3.7 equipment: Ultrasonic Doppler foetal heartbeat detector.
3.8 nominal acoustic working frequency: Value of the acoustic working frequency
quoted by the designer or manufacturer.
3.9 output power: Time-average ultrasonic power radiated by an ultrasonic transducer
into an approximately free field under specified conditions in a specified medium,
preferably in water.
[3.5 of IEC 1161].
Symbol: P
Unit: watt. W
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SIST EN 61266:2002
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1266 ©IEC:1994
3.10 overall sensitivity: Measure of the ability of an ultrasonic Doppler foetal heartbeat
detector to detect, above the noise level, a Doppler signal from a simulated point target
reflection loss, moving
(less than three wavelengths wide) of known target plane -wave
at a specified velocity and placed at a specified distance from the probe. The overall
sensitivity level,
S, in decibels (dB) is determined from:
S =A(d) +B+C
where
-wave reflection loss (dB) for the target at a distance d from
A(d) is the target plane
the probe;
B is the two-way attenuation over the acoustic pathway (dB), including that of the
acoustic attenuator(s), any coupling window and water path;
C is the signal-to-noise ratio (dB).
Symbol: S
Unit: decibel, dB
3.11 probe: An assembly, including the ultrasonic transducer element(s), which is
dedicated to the transmission and reception of ultrasound energy. It may also include
other components as necessary.
3.12 receiver unit: Part of the equipment which processes the ultrasonic signals from
the probe to produce at least a Doppler signal in the audible frequency range.
3.13 signal output part: Part of the equipment not being an applied part, intended to
deliver output signal voltages or currents to other equipment, for example, for display,
recording or data processing.
[2.1.19 of IEC 601-1].
is usually a terminal
NOTE - For an ultrasonic Doppler foetal heartbeat detector, the signal output part
receiver unit which allows connection of an earphone, headphone,
or connector at the output of the
speaker or other audio equipment.
3.14 spatial-peak temporal-peak acoustic pressure: Larger of the maximum positive
or modulus of the maximum negative instantaneous acoustic pressure in an acoustic field.
[3.26, 3.27 and 3.50 of IEC 1102].
Unit: pascal, Pa
3.15 target plane-wave reflection loss: Ratio (dB) of the acoustic pressure at a
specified distance from a target, in the ultrasonic field 180° back-reflected from the target,
to the acoustic pressure in the plane wave incident coaxially with the target axis of sym-
metry and at the position of the target if the target were removed.
Target plane-wave reflection loss is expressed as a positive number.
Symbol: A
Unit: decibel, dB
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SIST EN 61266:2002
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1266 © IEC:1994
which generates a high-frequency
transmitter unit: Part of the equipment
3.16
probe.
continuous wave or quasi-continuous wave electrical signal for energising the
4 List of symbols
a = radius of a ball or rod target
A(d) = target plane-wave reflection loss (dB) at a distance d
B = two-way attenuation (dB) over a total acoustic path
= two-way insertion loss (dB) of an acoustic attenuator
B a
BW = two-way insertion loss (dB) of a coupling window
C = signal-to-noise ratio (dB)
c = speed of sound in a medium
probe
distance between a target and the face of an ultrasonic transducer or
d =
f = ultrasonic frequency
k = (= 2n/k) circular wavenumber
of an ultrasonic transducer
P = output power
P = audio output power
Pa
of an ultrasonic Doppler foetal heartbeat detector
S = overall sensitivity
thickness of an acoustic window
t =
= hydrophone or ultrasonic transducer peak-to-peak signal at the position of a target
= hydrophone or ultrasonic transducer peak-to-peak signal at a specified distance
Ut
from a target
VS = r.m.s. Doppler signal
= r.m.s. noise
Vn
Z = Electrical impedance
a = Amplitude attenuation coefficient of plane waves in a medium
= Ultrasonic wavelength
5 Configuration
normally comprises the following modules (which may or may not be
The equipment
incorporated within the same housing), as shown in figure 1:
- probe;
- transmitter unit;
- receiver unit;
- signal output part.
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SIST EN 61266:2002
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1266 © IEC:1994
6 Performance
6.1 Acoustic working frequency
nominal
shall not deviate more than ±15 % from the
The acoustic working frequency
value stated by the manufacturer in accordance with
acoustic working frequency
clause 10.
Compliance is checked by measurement in accordance with the test method given in 8.1.
7 Safety
series dealing
shall comply with IEC 601-1 and any in the IEC 601 -2-X
The equipment
with foetal heartbeat detectors.
8 Tests
All measurements shall be undertaken using degassed water at a temperature of
22 °C ± 5 °C.
8.1 Acoustic working frequency
equipment shall be determined using the
The acoustic working frequency of the
acoustic coupling method shown in figure 2. The hydrophone shall comply with IEC 866 as
a class-B hydrophone. The active element of the hydrophone shall be positioned in the
centre, and at least 5 cm from the side and bottom walls, of the water vessel. Acoustic
absorbers shall be used to line the vessel in order to reduce stray reflections. The hydro-
operates in true continuous
phone shall be aligned for maximum signal. If the equipment
acoustic
wave mode then a frequency counter may be used for the determination of the
In this case, the amplifier may be omitted if the frequency counter
working frequency.
has sufficient sensitivity. The frequency counter used for this purpose shall have a flat
nominal acoustic working
frequency response range greater than 140 % of the
frequency of the equipment.
operates in any other mode such as quasi-continuous or swept
If the equipment
acoustic working frequency shall be determined from the waveform
frequency mode, the
detected by the hydrophone, using an oscilloscope and the zero-crossing method,
shall be
see IEC 854. For multiple frequency equipment, acoustic working frequency
(see clause 10). For
measured for each stated nominal acoustic working frequency
equipment, acoustic working frequency shall be measured at the lower
swept frequency
and upper frequencies of the swept frequency range (see clause 10).
shall
acoustic working frequency
The overall accuracy of the measurement of the
be ±1 % at the 95 % confidence level.
8.2 Output power
shall be determined using a radiation force balance in accordance with
Output power
IEC 1161 or using a hydrophone and spatially integrating the square of the acoustic
pressure following the procedures given in IEC 1101 and IEC 1102. The overall uncer-
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SIST EN 61266:2002
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1266 © IEC:1994
shall be better than ±50 % or better than ±4 mW,
tainty of measurement of output power
is such
output power
whichever is greater at the 95 % confidence level. If, however, the
does not comply with clause 6 of IEC 1157, the overall uncertainty of
equipment
that the
shall be better than ±30 % at the 95 % confidence level.
measurement of output power
The calibration of the measuring instrument should be traceable to National Measurement
Standards.
Spatial-peak temporal-peak acoustic pressure
8.3
shall be determined in the whole
The spatial-peak temporal-peak acoustic pressure
ultrasonic field using the test method in IEC 1102, or its equivalent. The hydrophone shall
conform to IEC 866 and IEC 1102. The hydrophone should be calibrated by reciprocity or
planar scanning methods given in IEC 866 or IEC 1101, or by any other method which has
been shown to yield equivalent or better accuracy. Where appropriate, the calibration of
the hydrophone should be traceable to National Measurement Standards.
in the whole ultrasonic field occurs
If the spatial-peak temporal-peak acoustic pressure
-
spatial-peak temporal
at a distance from the face of the probe less than 5 mm, then the
shall be determined in the part of the field where the distance
peak acoustic pressure
from the face of the probe is at least 5 mm.
Effective area of the ultrasonic transducer active element
8.4
shall be determined by
The effective area of the ultrasonic transducer active element
scanning a hydrophone in a plane perpendicular to the direction of the ultrasound beam
and at a distance of 5 mm from the face of the probe using the method specified in 8.1.5
of IEC 1102.
8.5 Overall sensitivity
shall be determined using the method described in 8.5.1 and 8.5.2
The overall sensitivity
equipment. The uncer-
which is aimed at simulating the actual conditions of use of the
tainties of the test methods (at the 67 % confidence level) should not exceed:
- target reflection loss ±3 dB;
±3 dB;
- reproducibility
±6 dB.
overall accuracy
The determination of the overall sensitivity shall be undertaken using a small vibrating
probe. Figure 3 shows a block
target placed in the ultrasonic field generated by the
diagram which illustrates the basic concept of the test method.
8.5.1 Test equipment
Target reflector
8.5.1.1
reflection loss at the acoustic
A small target reflector with a known target plane-wave
working frequency shall be used (see annex A). The target reflector diameter shall be
working frequency. The target may be
not more than three wavelengths at the acoustic
a small ball or alternatively a point target (such as a long rod with a flat or hemispherical
end). The target should be made of a material with a characteristic acoustic impedance in
target plane-wave reflection
to 3,5 x 10 6 kg m-2 s-1 . The
the range 0,6 x 10 6 kg m-2 s-1
loss shall be known to within ±3 dB over the range of frequencies for which it is used.
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The target plane-wave reflection loss shall be determined at the acoustic working
frequency of the equipment under test. For multiple frequency or swept frequency
equipment, the target plane-wave reflection loss shall be determined over the range of
acoustic working frequencies.
The target plane-wave reflection loss shall be determined with the orientation of the axis
of the target in relation to the incident ultrasound beam identical to that used in the
determination of the overall sensitivity specified in 8.5.2. Annex A gives information on
the test methods that may be used.
The target plane-wave reflection loss shall be determined for the four distances 50, 75,
100 and 200 mm.
Driving unit
8.5.1.2
The target shall be attached to an electro-mechanical driving unit which produces a
sawtooth oscillation with constant velocity over the mid-region of the excursion. The ampli-
tude of motion of the target should be such that the whole of the target, or the tip of the
target in the case of a long rod, is immersed in the water at all times. The excitation
frequency and the amplitude should be such as to give a target velocity in the range
10 cm/s to 40 cm/s. The Doppler frequency and target velocity shall be specified
(see clauses 9 and 10). This measurement shall be made between the extreme excursions
of the target, as shown in figure 4, and over a region of the waveform after the waveform
has stabilised. The distance between the target and the probe face shall be adjustable.
8.5.1.3 Test vessel
A test vessel should be used (see annex B for a typical example) incorporating an acous-
tically transparent window to which the probe is coupled using an acoustical coupling
medium. The lateral position of the probe shall be adjustable for alignment purposes. The
orientation of the probe shall be such that the ultrasound beam is approximately aligned
with the axis of the test vessel. Care shall be taken to avoid spurious movement of any
ace, except that of the target, which may be in the field of the probe. Acoustic
su rf
absorbers shall also be used to line the test vessel and shall be placed on the water
ace to surround the target support.
su rf
NOTE - Annex B illustrates a test vessel with the probe coupled through an acoustic window and the
probe. An alternative test vessel could utilise a target at the
vibrating target placed vertically above the
bottom of the test vessel with the probe face immersed in water. This latter configuration allows easier
insertion of the acoustical attenuators (see 8.5.1.6) without introducing a change in probe target distance.
R.M.S. signal measurement
8.5.1.4
A method of determining the r.m.s. level of the signal at the signal output part shall be
used, as specified in 8.5.1.2. If an r.m.s. voltmeter is used, checks shall be made to
ensure that the reading represents the signal level in the mid-region during the excursions
of the target.
8.5.1.5 Speaker (audio output unit)
If an audio output is not available. a speaker or other audio output unit should be
connected to the signal output part of the equipment under test.
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SIST EN 61266:2002
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1266 ©IEC:1994
Acoustic attenuator
8.5.1.6
Acoustic attenuators shall be inserted in the ultrasonic field between the probe and the
target in order to make realistic conditions in terms of the Doppler shifted echo level from
the target. The position of the attenuators shall be as close to the probe as possible. A set
ion losses to cover the range of
of attenuators shall be used having a range of inse rt
sensitivities to be measured. The thickest attenuator shall have a two-way insertion loss of
more than 20 dB. The attenuators shall be sheets of material of thickness constant
to ±0,05 mm and should have a front-face amplitude reflection coefficient of less
than 25 %. The two-way insertion loss (attenuation) shall be measured in advance of, or
during this overall sensitivity test (see annex C). The accuracy of the insertion loss of
±1
dB or better at the 95 % confidence limit over the range of
each attenuator shall be
When several attenuators are used in series, the total
acoustic working frequencies.
thickness of the attenuator shall be no more than 20 mm. Care should be taken to ensure
rfaces of the attenuators. Water or any other suitable
that no air is trapped between the su
acoustic coupling medium.
liquid or gel should be used as the
B for ultrasound passing from the probe to the target and
The total two-way attenuation
rtion loss of any acoustic
back shall be determined. This attenuation shall include the inse
coupling window of the water vessel (i.e. the bottom plate in the example shown in
figure 3). The total two-way attenuation is therefore given by:
B =EBa+BW
where
E Ba is the total insertion loss of the bank of attenuators;
BW is the inse rtion loss across any coupling window.
may be neglected under certain conditions (see annex C).
BW
8.5.2 Measuring procedure
shall be performed as
equipment
The measurement of the overall sensitivity of the
follows (by reference to the example of a test system shown in figure 3).
8.5.2.1 The water vessel shall be filled and the test equipment set up with the probe
face approximately in the centre of the test vessel and its orientation aligned visually such
d, between
that the ultrasound beam is directed to impinge on the target. The distance,
the probe and the target is set to one of the distances specified in 8.5.2.6. The orientation
of the target in relation to the ultrasound beam shall be identical to that used for the deter-
mination of the target reflection loss (see 8.5.1.1).
8.5.2.2 An r.m.s. measurement system is connected to the signal output part. A CRT
oscilloscope is connected to the electrical signal of the target drive unit and the
under test. The probe is connected to the test equipment as shown in figure 3.
equipment
8.5.2.3 The volume control on the equipment under test is set to a position to obtain a
measurable value of Vn (r.m.s.) (the electrical noise output of the equipment) when the
target is not in motion. The driving unit is operated to obtain a Doppler signal and the
lateral positions of the probe unit are adjusted in order to maximise the output amplitude.
S (r.m.s.) (signal and noise together) is measured at the same position of the
The output V
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SIST EN 61266:2002
1266 ©IEC:1994 — 25 —
volume control as that used previously. The output of the equipment under test is reduced
by adding acoustic attenuators between the probe and the target until the signal-to-noise
ratio, C, is approximately 6 dB, where C is given in decibels by:
(vs (r.m.s.)
C = 20 logio
Vn (r.m.s.)
The overall sensitivity, S, (dB) is then given by:
S =A(d) +B+C
where
A(d) is the target plane-wave reflection loss (dB) at the distance d (see 8.5.1.1 and
annex A)
B is the two-way attenuation over the acoustic pathway (dB) including that of the
acoustic attenuator(s), any coupling window and water path (see annex C);
C is the signal-to-noise ratio (dB).
8.5.2.4 In order to ensure that the Doppler signals can be heard, under condition of a
Pa, should be such that Pa >1 mW
signal-to-noise ratio C = 6 dB, the audio output power,
for a speaker drive output and Pa >100 pW for an earphone or headphone drive output,
a, is calculated from:
when the volume control is set at its maximum. The power, P
= Vn2
Pa (r.m.s.)/Zv
where Z is the nominal electrical impedance of the substantially resistive load.
8.5.2.5 If a ball target is used, the determination of the overall sensitivity shall be
undertaken using two targets of different diameter. The ratio of the diameter of the larger
target to that of the smaller target shall be greater than 1,1. The declared values of the
overall sensitivity shall be taken from the data from the target giving the larger value
of S. See annex A.
8.5.2.6 The overall sensitivity, S, shall be determined with the target positioned at the
distances (d) of 50, 75, 100 and 200 mm from the face of the probe.
NOTE — The aim here is to determine sensitivity over the range of distances used clinically. The largest
distance of 200 mm is specified to represent a distant target and is therefore a relatively de
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