SIST EN 61391-1:2008

SLOVENSKI STANDARD
01-februar-2008
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Ultrasonics - Pulse-echo scanners - Part 1: Techniques for calibrating spatial
measurement systems and measurement of system point-spread function response (IEC
61391-1:2006)
Ultraschall - Impuls-Echo-Scanner - Teil 1: Verfahren für die Kalibrierung von räumlichen
Messsystemen und Messung der Charakteristik der Punktverwaschungsfunktion des
Systems (IEC 61391-1:2006)
Ultrasons - Scanners à impulsion et écho - Partie 1: Techniques pour l'étalonnage des
systèmes de mesure spatiaux et des mesures de la réponse de la fonction de dispersion
ponctuelle du système (CEI 61391-1:2006)
Ta slovenski standard je istoveten z: EN 61391-1:2006
ICS:
11.040.55
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61391-1
NORME EUROPÉENNE
October 2006
EUROPÄISCHE NORM
ICS 17.140.50
English version
Ultrasonics -
Pulse-echo scanners
Part 1: Techniques for calibrating spatial measurement systems
and measurement of system point-spread function response
(IEC 61391-1:2006)
Ultrasons -  Ultraschall -
Scanners à impulsion et écho Impuls-Echo-Scanner
Partie 1: Techniques pour l'étalonnage Teil 1: Verfahren für die Kalibrierung
des systèmes de mesure spatiaux von räumlichen Messsystemen
et des mesures de la réponse de und Messung der Charakteristik
la fonction de dispersion ponctuelle der Punktverwaschungsfunktion
du système des Systems
(CEI 61391-1:2006) (IEC 61391-1:2006)

This European Standard was approved by CENELEC on 2006-10-01. 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, 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

© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61391-1:2006 E
Foreword
The text of document 87/336/FDIS, future edition 1 of IEC 61391-1, prepared by IEC TC 87, Ultrasonics,
was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61391-1 on
2006-10-01.
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) 2007-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2009-10-01
Terms 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 61391-1:2006 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 61828 NOTE  Harmonized as EN 61828:2001 (not modified).
IEC 61157 NOTE  Harmonized as EN 61157:1994 (not modified).
__________
- 3 - EN 61391-1:2006
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 61102 1991 Measurement and characterisation of EN 61102 1993
ultrasonic fields using hydrophones in the
frequency range 0,5 MHz to 15 MHz

IEC 61685 2001 Ultrasonics - Flow measurement systems - EN 61685 2001
Flow test object
NORME CEI
INTERNATIONALE
IEC
61391-1
INTERNATIONAL
Première édition
STANDARD
First edition
2006-07
Ultrasons – Scanners à impulsion et écho –
Partie 1:
Techniques pour l'étalonnage des systèmes
de mesure spatiaux et des mesures de la réponse
de la fonction de dispersion ponctuelle du système

Ultrasonics – Pulse-echo scanners –
Part 1:
Techniques for calibrating spatial measurement
systems and measurement of system point-spread
function response
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For price, see current catalogue

61391-1  IEC:2006 – 3 –
CONTENTS
FOREWORD.5
INTRODUCTION.9

1 Scope.11
2 Normative references.11
3 Terms and definitions .11
4 Symbols .23
5 General conditions.23
6 Techniques for calibrating 2D-measurement systems .27
6.1 Test methods .27
6.2 Instruments .27
6.3 Test settings.29
6.4 Test parameters .31
7 Methods for calibrating 3D-measurement systems.35
7.1 General .35
7.2 Types of 3D-reconstruction methods.37
7.3 Test parameters associated with reconstruction problems .39
7.4 Test methods for measurement of 3D-reconstruction accuracy.41
8 Measurement of point-spread and line-spread functions (high-contrast spot size) .49
8.1 General .49
8.2 Test methods .51
8.3 Instruments .51
8.4 Test settings.51
8.5 Test parameters .57

Annex A (normative) Test objects – Calibration of 2D-spatial measurement systems.67
Annex B (normative) Test objects – Measurement and calibration of 3D-image
reconstruction accuracy .73
Annex C (normative) Test objects – Measurement of point-spread function response.79

Bibliography .89

61391-1  IEC:2006 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
ULTRASONICS – PULSE-ECHO SCANNERS –

Part 1: Techniques for calibrating spatial measurement systems
and measurement of system point-spread function response

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 61391-1 has been prepared by IEC technical committee 87:
Ultrasonics.
The text of this standard is based on the following documents:
FDIS Report on voting
87/336/FDIS 87/343/RVD
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.

61391-1  IEC:2006 – 7 –
Terms in bold in the text are defined in clause 3.
This standard is intended to be published in two or more parts:
– Part 1 deals with techniques for calibrating spatial measurement systems and
measurement of system point-spread function response;
– Part 2 will deal with measurement of system sensitivity, dynamic range, and low-contrast
resolution.
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.
61391-1  IEC:2006 – 9 –
INTRODUCTION
An ultrasonic pulse-echo scanner produces images of tissue in an ultrasonic scan plane by
sweeping a narrow pulsed beam of ultrasound through the section of interest and detecting
the echoes generated at tissue boundaries. A variety of ultrasonic transducer types are
employed to operate in a transmit/receive mode for the ultrasonic signals. Ultrasonic scanners
are widely used in medical practice to produce images of many soft-tissue organs throughout
the human body.
This standard describes test procedures that should be widely acceptable and valid for a wide
range of types of equipment. Manufacturers should use the standard to prepare their
specifications; the users should employ the standard to check specifications. The
measurements can be carried out without interfering with the normal working conditions of the
machine. Typical test objects are described in the annexes. The structures of the test objects
have not been specified in detail, rather suitable types of overall and internal structures are
described. The specific structure of a test object should be reported with the results obtained
using it. Similar commercial versions of these test objects are available.
The performance parameters specified and the corresponding methods of measurement have
been chosen to provide a basis for comparison with the manufacturer's specification and
between similar types of apparatus of different makes, intended for the same kind of diagnostic
application. The manufacturer's specification should allow comparison with the results obtained
from the tests in this standard. Furthermore, it is intended that the sets of results and values
obtained from the use of the recommended methods will provide useful criteria for predicting
the performance of equipment in appropriate diagnostic applications. This standard
concentrates on measurements of images by digital techniques. Methods suitable for
inspection by eye are covered here as well. Discussion of other visual techniques can be found
1)
in IEC 61390 [1] .
Where a diagnostic system accommodates more than one option in respect of a particular
system component, for example the ultrasonic transducer, it is intended that each option be
regarded as a separate system. However, it is considered that the performance of a machine is
adequately specified, if measurements are undertaken for the most significant combinations of
machine control settings and accessories. Further evaluation of equipment is obviously
possible but this should be considered as a special case rather than a routine requirement.
___________
)
Figures in square brackets refer to the Bibliography.

61391-1  IEC:2006 – 11 –
ULTRASONICS – PULSE-ECHO SCANNERS –

Part 1: Techniques for calibrating spatial measurement systems
and measurement of system point-spread function response

1 Scope
This International Standard describes methods of calibrating the spatial measurement facilities
and point-spread function of ultrasonic imaging equipment in the ultrasonic frequency range
0,5 MHz to 15 MHz. This standard is relevant for ultrasonic scanners based on the pulse-echo
principle of the types listed below:
− mechanical sector scanners;
− electronic phased-array sector scanners;
− electronic linear-array scanners;
− electronic curved-array sector scanners;
− water-bath scanners based on any of the above four scanning mechanisms;
− 3D-volume reconstruction systems.
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 61102:1991, Measurement and characterisation of ultrasonic fields using hydrophones in
the frequency range 0,5 MHz to 15 MHz

IEC 61685:2001, Ultrasonics – Flow measurement systems – Flow test object
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
See also related standards and technical reports for definitions and explanations. [1-5]
3.1
A-scan
class of data acquisition geometry in one dimension, in which echo strength information is
acquired from points lying along a single beam axis and displayed as amplitude versus time of
flight or distance
61391-1  IEC:2006 – 13 –
3.2
acoustic coupling agent (also, coupling agent)
a material, usually a gel or other fluid, that is used to ensure acoustic contact between the
transducer and the patient’s skin, or between the transducer and the surface of a sealed test
object
3.3
acoustic working frequency
arithmetic mean of the frequencies f and f at which the amplitude of the acoustic pressure
1 2
spectrum is 3 dB below the peak amplitude
(See 3.4.2 of IEC 61102)
3.4
automatic time-gain compensation
ATGC
automatic working time gain control based on the observed decrease in echo amplitudes due to
the attenuation in ultrasonic pulse amplitude with depth
3.5
axial resolution
minimum separation along the beam axis of two equally scattering volumes or targets at a
specified depth for which two distinct echo signals can be displayed
3.6
backscatter coefficient
mean acoustic power scattered in the 180º direction by a specified object with respect to the
direction of the incident beam, per unit solid angle per unit volume, divided by the incident
beam intensity. For a volume filled with many scatterers, the scatterers are considered to be
randomly distributed. The mean power is obtained from different spatial realisations of the
scattering volume
NOTE Backscatter coefficient is commonly referred to as the differential scattering cross-section per unit volume
in the 180° direction
3.7
backscatter contrast (normalized)
difference between the backscatter coefficients from two defined regions divided by the
square root of the product of the two backscatter coefficients
3.8
beam axis
the longitudinal axis of the pulse-echo response pattern of a given B-mode scan line, a
pulse-echo equivalent to the transmitted beam axis of IEC 61828 [2]
3.9
B-scan
class of data acquisition geometry in which echo information is acquired from points lying in an
ultrasonic scan plane containing interrogating ultrasonic beams. See B-mode below.
NOTE B-scan is a colloquial term for B-mode scan or image. (See 3.10)

61391-1  IEC:2006 – 15 –
3.10
Brightness-modulated display
B-mode
method of presentation of B-scan information in which a particular section through an imaged
object is represented in a conformal way by the scan plane of the display and echo amplitude is
represented by local brightness or optical density of the display
[IEC 60854: definition 3.18, modified]
3.11
displayed dynamic range
ratio, expressed in decibels, of the amplitude of the maximum echo that does not saturate the
display to the minimum echo that can be distinguished in the display under the scanner test
settings
3.12
elevational resolution
minimum separation perpendicular to the ultrasonic scan plane of two equally scattering
targets at a specified depth for which two distinct echo signals can be displayed. Often used
here informally for slice thickness for purposes of 3D-scanning
3.13
field-of-view
area in the ultrasonic scan plane which is insonated by the ultrasound beam during the
acquisition of echo data to produce one image frame
3.14
frame rate
number of sweeps comprising the full-frame refresh rate that the ultrasonic beam makes per
second through the field-of-view
3.15
gain
ratio of the output to the input of a system, generally an amplifying system, usually expressed
in decibels
3.16
grey scale
range of values of image brightness, being either continuous between two extreme values or, if
discontinuous, including at least three discrete values
[IEC 60854: definition 3.14]
3.17
lateral resolution
minimum separation of two line targets at a specified depth in a test object made of
tissue-mimicking material for which two distinct echo signals can be displayed. The line
targets should be perpendicular to the scanned plane; the separation between the targets
should be perpendicular to the beam-alignment axis
3.18
line-spread function
LSF
characteristic response in three dimensions of an imaging system to a high-contrast line target

61391-1  IEC:2006 – 17 –
3.19
line target
cylindrical reflector whose diameter is so small that the reflector cannot be distinguished by the
imaging system from a cylindrical reflector with diameter an order of magnitude smaller, except
by signal amplitude. The backscatter from a standard line target should be a simple function
of frequency over the range of frequencies studied
3.20
M-mode
time-motion mode
method of presentation of M-scan information in which the motion of structures along a fixed
beam axis is depicted by presenting their positions on a line which moves across a display to
show the variation with time of the echo
3.21
M-scan
time-motion scan
class of acquisition geometry in which echo information from moving structures is acquired
from points lying along a single beam axis. The echo strength information is presented using
an M-mode display
3.22
nominal frequency (of a transducer)
intended acoustic working frequency of a transducer as quoted by the designer or
manufacturer
[adapted from definition 3.7 of IEC 60854]
3.23
pixel
picture element
smallest spatial unit or cell size of a digitized 2-dimensional array representation of an image.
Each pixel has an address (x-and y-coordinates corresponding to its position in the array) and
a specific brightness level
NOTE Pixel is a contraction of ‘picture element’.
3.24
point target
reflector whose scattering surface dimensions are so small that it cannot be distinguished
(except by signal amplitude) by the imaging system from a similar target whose scattering
surface is an order of magnitude smaller. The backscatter cross section of a standard point
target should be a simple function of frequency over the range of frequencies studied.
3.25
point-spread function
PSF
characteristic response in three dimensions of an imaging system to a high-contrast point
target.
NOTE For most ultrasound systems, an individual ultrasound PSF cannot be used as the overall system impulse
response, due to changes in the PSF with depth, with other positions in the region of use and with system focal and
frequency settings.
61391-1  IEC:2006 – 19 –
3.26
scan line
one of the component lines which form a B-mode image on an ultrasound monitor. Each line is
the envelope-detected A-scan line in which the echo amplitudes are converted to brightness
values
3.27
scan plane
a plane containing the ultrasonic scan lines
[IEC 61102: definition 3.38, modified]
3.28
side lobe
secondary beam, generated by an ultrasonic transducer, that deviates from the direction of
the main beam. Usually, the intensity of the side lobes is significantly less than that of the
central axis beam
NOTE The presence of side lobes may be responsible for introducing artifactual echoes into the ultrasound
image.
3.29
slice thickness
thickness, perpendicular to the ultrasonic scan plane and at a stated depth in the test object,
of that region of the test object from which acoustic information is displayed
3.30
speckle pattern
image pattern or texture, produced by the interference of echoes from the scattering centres in
tissue or tissue-mimicking material
3.31
spot size
the –6 dB width or otherwise specified width of the PSF or LSF
3.32
target
an object to be interrogated by an ultrasound beam
NOTE Examples of targets are:
a) a device specifically designed to be inserted into the ultrasonic field to serve as the object on which the
radiation force is to be measured;
b) a scatterer or ensemble of scatterers giving rise to a signal within the effective ultrasonic beam;
c) a wire or a filament in a test object.

3.33 test object
device containing one or more groups of object configurations embedded in a tissue-
mimicking material or another medium
3.34 test object scanning surface
surface on the tissue-mimicking test object recommended for transducer location during a test
procedure
61391-1  IEC:2006 – 21 –
3.35
time-gain compensation
TGC
change in amplifier gain with time, introduced to compensate for loss in echo amplitude with
increasing depth due to attenuation in tissue
3.36
tissue-mimicking material
material in which the propagation velocity (speed of sound), reflecting, scattering and
attenuating properties are similar to those of soft tissue for ultrasound in the frequency range
0,5 MHz to 15 MHz.
[See 6.4 and Annex D of IEC 61685]
3.37
transmitted ultrasound field
three-dimensional distribution of ultrasound energy emanating from the ultrasonic transducer
3.38
ultrasonic scan line
for automatic scanning systems, the beam-alignment axis either for a particular ultrasonic
transducer element or for a single or multiple excitation of an ultrasonic transducer or of an
ultrasonic transducer element group
[IEC 61157: definition 3.27, modified]
3.39
ultrasonic transducer
device capable of converting electrical energy to mechanical energy within the ultrasonic
frequency range and/or reciprocally capable of converting mechanical energy to electrical
energy
[IEC 61102: definition 3.58]
NOTE For the purposes of this standard, ultrasonic transducer is taken to refer to a complete assembly that
includes the transducer element or elements and mechanical and electrical damping and matching provisions.
3.40
ultrasonic transducer element group
group of elements of an ultrasonic transducer which are excited together in order to produce
a single acoustic pulse
[IEC 61102: definition 3.60]
3.41
ultrasound
acoustic oscillation whose frequency is above the high-frequency limit of audible sound
(conventionally 20 kHz)
[IEV 801 21-04, modified]
3.42
ultrasound beam (pulse-echo response pattern)
region adjacent to the transducer face from which an echo signal from a specified target may
be detected for the test settings of the scanner and with the scanner operating in a
non-scanning mode. This term should be distinguished from the transmitted ultrasound field

61391-1  IEC:2006 – 23 –
3.43
voxel
smallest spatial unit or cell size of a digitized 3-dimensional array representation of an image.
Each voxel has an address (x, y, and z-coordinates) corresponding to its position in the array,
and a specific brightness and/or color value
3.44
working liquid
a mixture of water and other solvent that adjusts the speed of sound to 1 540 m/s
[See also 6.4 and Annex D of IEC 61685:2001]
4 Symbols
A surface area
A cross-sectional area
c
a length of the semi-major axes for a given half (i = 1 or 2) of the ellipsoid of an ovoid
i
object
b mean of the lengths of the minor axes of the ellipsoid of an ovoid object
f acoustic working frequency
k circular wave number;( = 2π / λ in which λ is the wavelength)
P perimeter of cross-section of ovoid object
R ratio of mean of measured spacings to known spacings (see 7.3.1)
R lateral dimension calibration factor (see 7.4.2);
x
ratio of mean filament spacings to known spacings for the horizontal direction
R ratio of mean filament spacings to known spacings for the vertical direction
y
r radius of a wire or filament target
V volume of an ovoid object
Z characteristic acoustic impedance of a wire or filament material
m
Z characteristic acoustic impedance of the surrounding medium (working liquid or
w
tissue-mimicking material)
ε 1-(b/(2a)) eccentricity of an ellipsoid or an ovoid object
σ backscattering cross-section for a point-like target
5 General conditions
The tests should be performed within the following ambient conditions:
− temperature 23 °C ± 3 °C;
− relative humidity 45 % to 75 %;
− atmospheric pressure 86 kPa to 106 kPa.
This standard permits the use of test objects of various constructions. Therefore it is essential
that the following data of the test object be reported. The following standard choices are
recommended:
61391-1  IEC:2006 – 25 –
a) medium: either working liquid or tissue-mimicking material [6]
b) use of coupling gel: thin layer or gel with adapted sound velocity
c) geometry (one of the models given in Annex A, B or C, where needed with a different
spacing between targets).
For the medium working liquid, the following properties are required:
– speed of sound = (1 540 ± 15) m/s;
-1 -1
– low attenuation (< 0,1 f dB cm MHz );
– negligible scattering (see IEC 61685).
For adjusting the speed of sound in working liquid, see [7, 8].
For the medium tissue-mimicking material [9], the following properties are required:
− speed of sound = (1 540 ± 15) m/s;
–1 –1
− attenuation (0,5 ± 0,05) f dB cm MHz ) in the frequency range used in the tests;
− scattering (moderate, no value imposed ).
Note: Where an ultrasound system is designed for particular applications where the mean speed of sound is
different from 1 540 m/s, a medium with that design speed of sound should be employed and that change reported
with the results.
For tissue-mimicking properties, see also 6.4 and Annex D of IEC 61685:2001 .
Tissue-mimicking material is usually protected by a thin cover. Its thickness and acoustic
properties (attenuation and sound velocity) should be reported if these influence the
measurement.
The transducer is usually coupled to the cover of tissue-mimicking material by an acoustic
coupling agent (ultrasound gel). If the layer is thin (compared to the wavelength) its influence
can be ignored. For a thick layer, for example as needed for a curved-array transducer, the
sound velocity of the acoustic coupling agent shall be equal to (1 540 ± 15) m/s.
Sound velocity of a medium has two different effects: if it is larger then 1 540 m/s, the axial
distances in the medium are rendered proportionally shorter and the focus of the transducer
moves away from the transducer. If the sound velocity is lower, the opposite occurs. The effect
on the focus becomes more important for transducers with a high numeric aperture. Therefore
the use of the correct sound velocity (1 540 ± 15) m/s, to which ultrasonic systems are
standardized) is essential in Clauses 6 and 7, dealing with geometrical distortions. In Clause 8,
dealing with the PSF, a deviation can be tolerated for not too high numeric apertures.
In describing scanning procedures with “horizontal” and “vertical”, it is assumed that a test
object is insonated from above, and that the image on the scanner is oriented correspondingly.

61391-1  IEC:2006 – 27 –
6 Techniques for calibrating 2D-measurement systems
6.1 Test methods
To carry out the test procedures, the following items are required:
a) tissue-mimicking test objects containing targets at accurately specified positions;
b) tissue-mimicking test object containing a 3D-object of accurately specified dimensions;
c) a tank containing degassed working liquid.
The specifications of these devices are given in the annexes.
6.2 Instruments
6.2.1 General
The equipment specified in this subclause has been selected to permit testing of ultrasonic
scanners in clinical usage. The devices described will ensure that the data collection and
analysis will be objective and reproducible.
6.2.2 Digitizers
While some spatial measurements can be made with long-existing digital callipers, for more
generally applicable, objective, reproducible data, the ultrasound images obtained for testing
should be digitally encoded. Many modern ultrasound imaging devices produce digital images
from the scan converter that can be used for these measurements and are most closely
representative of the displayed images. Such measurements can be employed well by hospital-
based users with some digital measurement expertise. For spatial measurements this
procedure is directly applicable. For PSF and LSF measures it is necessary, however, to have
a characteristic curve of linear echo amplitude at the transducer as a function of the digital
image values or to create a sparse representation of that curve by use of calibrated reflectors
as described in 7.2.1.2 of [19]. In some systems, rf scan-line data are available. Such data are
more accurate for precision measurements in which the linear signal amplitude is important.
Measurements made with rf data should be clearly indicated as such and the level at which
they came from the system documented. For those machines that do not produce digital
images, a frame grabber may be used to acquire and digitize ultrasound images. This digitizer
requires adequate spatial resolution (at least 512 × 512 pixels) and sufficient grey scale (at
least 256 grey shades). Also, adequate image analysis software should be used to perform the
simple measurements described below on the digital ultrasound images of the test objects.
The digitizer shall exhibit a linearity producing spatial uncertainty of <1 % over 75 % of the
image dimension measured, signal level (grey scale) linearity <3 % of full range and signal
level stability over a year of <5 % of full range.
The digital imaging software should allow the user to be able to place the cursor at any location
on the screen and obtain the pixel address (i.e. row, column coordinates). This will allow the
user to calibrate the digital image to actual distances recorded in the ultrasound images. Once
the digitizer is calibrated, digitized ultrasound images can be subjected to more sophisticated
software analysis than that which is possible directly on the ultrasound display. The digital
imaging software should allow the reading of the grey value at any pixel address.

61391-1  IEC:2006 – 29 –
To calibrate the digital image pixel distance (i.e. calibrate the digitizer relative to the
ultrasound imaging system):
a) Scan an image of a test object containing appropriate working liquid. Make a note of the
magnification level for this image and make all subsequent measurements and
comparisons with the same level of magnification.
b) Measure the known distances between the positions of two wires or filaments at a distance
of about 75 % of the screen size with the electronic callipers to confirm that the calliper
measured distance corresponds to the actual distance. The measurement should be
performed for a pair of wires or filaments connected by a vertical line and for a pair of wires
or filaments connected by a horizontal line. In case deviations are found the scanner should
be adjusted before proceeding further. If adjustment is not possible the actual distances
shall be used in d).
c) Digitize the scanned image and use the imaging software to measure the distances in
pixels between pairs of wires or filaments by obtaining the pixel address of each wire or
filament location, and subtracting to obtain the distances in pixels. Repeat for several
different locations, checking both vertical and horizontal distances.
d) Measure the distance in pixels for various positions of wires, using various directions of the
connecting line with respect to the vertical. Divide each distance by the actual distance in
mm. Average these ratios; this average ratio is the pixels per millimetre calibration for your
digitizer. Once this calibration has been performed, this ratio can be used to compute
relative distances in all subsequent digitized images for the particular scanner and
magnification used.
See [10].
6.2.3 Tissue-mimicking test objects
Tissue-mimicking test objects shall contain structures that allow the following types of
measurement to be made:
a) linear;
b) curvilinear;
c) circumferential;
d) area;
e) volume;
f) image distortion;
g) M-mode calibration.
Examples of tissue-mimicking test objects are given in Annex B.
6.3 Test settings
6.3.1 General
The many combinations of scanner settings and transducers make it impracticable to carry out
tests for all of them. Tests are therefore carried out for each ultrasonic transducer. with two
settings, one which provides a complete image and one which provides the highest resolution
of the test objects. The focusing of the ultrasonic beam should be extended over as large a
range as possible, to achieve the best resolution over all visible targets.
The test object, containing an array of filaments as in Figure A.1, is used for the procedures
described below.
61391-1  IEC:2006 – 31 –
6.3.2 Display settings (focus, brilliance, contrast)
The focus is made sharp and the brilliance and contrast controls are turned to their lowest
positions. The brilliance is now increased until the echo-free zone at the side of the image
becomes the minimum perceptible shade of grey. The contrast control is then increased to
make the image contain the greatest range of grey shades possible. The focus is then checked
for sharpness. If it requires further adjustment, the whole procedure is repeated.
6.3.3 Sensitivity settings (frequency, suppression, output power, gain, TGC, ATGC)
a) The nominal frequency of the ultrasonic transducer is noted.
b) If there is a suppression- or reject-control, it is adjusted to allow the smallest possible
signals to be displayed.
c) The output power and gain are adjusted to present the images of the target filaments as
the smallest visible points on the display.
d) The time-gain compensation (TGC) controls are arranged to present the images of the
target with equal brilliance over the image. For scanning in working liquid the TGC slope
should be close to zero
6.3.4 Final optimisation
A final optimisation of the image may be carried out by a small change in the suppression level,
gain or output power.
When automatic time-gain compensation (ATGC) is an option in a scanner, tests should be
carried out in this mode of operation. The test object is imaged with ATGC enabled, the image
being optimised using any control which still functions manually, e.g. the overall gain or output
power.
6.3.5 Recording system
The digital acquisition of ultrasound images allows for objective measurements and also
allows the images to be saved for comparison at a later date. A major advantage of digital
recording is that images are not subjected to the degradation that occurs with either
photographic or video recording systems.
6.4 Test parameters
6.4.1 General
Techniques are described in this standard for the following types of measurement:
− linear;
− curvilinear;
− circumferential;
− area;
− volume;
− display and recording distortion;
− M-mode calibration.
61391-1  IEC:2006 – 33 –
Transmitted intensity should be low enough to avoid pulse distortion due to non-linear
propagation (see IEC 61102). A list of all factors influencing the operation of the scanner for
example transducer, frequency, sensitivity control settings, focusing, image processing option
shall be made. These data are to be recorded in sufficient detail so as to allow the test to be
repeated exactly at a later date by another operator and shall accompany the measuring
results.
6.4.2 Measurement accuracy (linear, curvilinear, circumferential, area)
To assess the accuracy of the measurement system of a scanner, the wires or filaments in the
test object shown in Figure A.1 or Figure A.2 are imaged with the sensitivity adjusted to make
the displayed echoes as sharp as possible. If the test object is sealed, a coupling agent shall
be used. An ultrasound image is obtained and digitized of the set of filament targets situated
at the middle of the typical working range for the ultrasonic transducer assembly being used.
Other factors that may affect the value of the resolution are also noted, for example the image
processing options of the scan converter or focusing. The procedure is repeated for the other
ultrasonic transducers of the scanner.
Measurements are made in straight lines on the screen of lengths approximately equal to 75 %
of the displayed range. Using image analysis software, a linear brightness profile is obtained
along each dimension. Distances are measured “from peak to peak” of the wire or filament
brightness profiles. (In case the measuring results are noisy, the position of a peak value is
replaced by the midpoint between the –3 dB points and that action noted.) These
measurements are carried out along at least a vertical and a horizontal line in Figures A.1, and
A.2 and, when possible, along near-vertical directions in the field-of-view. The average
percentage error is tabulated for each length in each direction. The process is repeated for the
available display scales.
To evaluate the accuracy of measurements of curved lines and cross-sectional areas, closed
figures having an area approximately 0,75 of the field-of-view are traced centrally on the
display. The circumferences and areas are measured and the percentage errors calculated.
The tracing is done point-to-point, so that a polygon-shaped region is traced. The
c
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