IEC TS 62558:2011

Ultrasonics - Real-time pulse-echo scanners - Phantom with cylindrical, artificial cysts in tissue-mimicking material and method for evaluation and periodic testing of 3D-distributions of void-detectability ratio (VDR)

IEC/TS 62558:2011(E) specifies essential characteristics of a phantom and method for the measurement of void-detectability ratio for medical ultrasound systems and related transducers. It is restricted to the aspect of long-term reproducibility of testing results. Medical diagnostic ultrasound systems and related transducers need periodic testing as the quality of medical decisions based on ultrasonic images may decrease over time due to progressive degradation of essential systems characteristics. The TMM (Tissue Mimicking Material) phantom is intended to be used to measure and to enable documentation of changes in void-detectability ratio in periodic tests over years of use. This technical specification establishes:
- Important characteristics and requirements for a TMM 3D artificial cyst phantom using anechoic voids
- A design example of a 3D artificial cyst phantom, the necessary test equipment and use of relevant computer software algorithms.
This technical specification is currently applicable for linear array transducers. A uniformity test prior to void-detectability ratio (VDR) measurement is recommended.

General Information

• Status: Published
• Publication Date: 22-Mar-2011
• ICS: 17.140.50 - Electroacoustics
• Technical Committee: TC 87 - Ultrasonics
• Drafting Committee: WG 9 - TC 87/WG 9
• Current Stage: PPUB - Publication issued
• Start Date: 23-Mar-2011
• Completion Date: 30-Apr-2011

Overview

IEC TS 62558:2011 specifies a test phantom and method for measuring and monitoring the void-detectability ratio (VDR) of medical diagnostic ultrasound systems. The document defines essential characteristics of a tissue‑mimicking material (TMM) 3D artificial‑cyst phantom with cylindrical anechoic voids and a measurement procedure to support long‑term, reproducible periodic testing of imaging performance. The technical specification is presently applicable to linear array transducers and includes a design example, required test equipment and software analysis approaches. A uniformity test prior to VDR measurement is recommended.

Key Topics and Requirements

• Phantom design: 3D TMM phantom composed of alternating “cyst” (anechoic) slices and attenuation slices to allow measurement across axial, azimuthal and elevation axes.
• Tissue‑mimicking material (TMM): Requirements for acoustic properties and stability so the phantom can document VDR changes over years.
• Anechoic voids: Cylindrical artificial cyst targets of defined diameters to evaluate detectability across frequencies (approx. 1–15 MHz in the example).
• Measurement principle: Procedures for acquiring digitized B/C/D images, defining regions of interest, and calculating VDR distributions in 3D.
• Test equipment and software: Recommendations for motorized scanning, data capture and image analysis algorithms to achieve reproducible VDR metrics.
• Stability and reproducibility: Specifications to ensure long‑term comparability of periodic tests and guidance on phantom enclosure, scanning surface and dimensional tolerances.
• Pre‑test uniformity check: A uniformity measurement is recommended to detect fixed pattern artifacts or probe element failures before VDR evaluation.

Applications and Who Uses It

Practical uses:

• Quality assurance (QA) and periodic performance monitoring of clinical ultrasound systems.
• Acceptance testing and longitudinal tracking of imaging degradation that could affect diagnostic decisions.
• Manufacturer self‑testing during development or production verification of transducers and imaging systems.
• Regulatory and accreditation programs that require objective imaging performance records.

Typical users:

• Biomedical engineers and clinical engineers
• Medical physicists and ultrasound QA technicians
• Ultrasound system and probe manufacturers
• Hospital QA managers and regulatory auditors

Related Standards (if applicable)

IEC TC 87 publishes standards and specifications for medical ultrasonics; IEC TS 62558 complements other IEC publications addressing diagnostic ultrasound equipment performance, safety and quality assurance. Users should consult current IEC publications for the latest related guidance and normative references.

Keywords: IEC TS 62558:2011, ultrasound phantom, void-detectability ratio, VDR, tissue-mimicking material, TMM, 3D artificial cyst phantom, periodic testing, medical diagnostic ultrasound, linear array transducers, quality assurance.

Standards Content (Sample)

IEC/TS 62558 ®
Edition 1.0 2011-03
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Real-time pulse-echo scanners – Phantom with cylindrical,
artificial cysts in tissue-mimicking material and method for evaluation and
periodic testing of 3D-distributions of void-detectability ratio (VDR)

IEC/TS 62558:2011(E)
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IEC/TS 62558 ®
Edition 1.0 2011-03
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Real-time pulse-echo scanners – Phantom with cylindrical,
artificial cysts in tissue-mimicking material and method for evaluation and
periodic testing of 3D-distributions of void-detectability ratio (VDR)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 17.140.50 ISBN 978-2-88912-377-3

– 2 – TS 62558  IEC:2011(E)
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Symbols . 11
5 Ambient conditions of measurement with the phantom . 12
6 Specification of TMM 3D artificial anechoic-cyst phantom . 12
6.1 3D-phantom concept . 12
6.2 General phantom specification . 12
6.3 TMM specifications: . 12
6.4 Anechoic targets . 13
6.5 Phantom enclosure. 13
6.6 Scanning surface: . 13
6.7 Dimensions . 13
6.8 Phantom stability . 14
6.9 Digitized image data . 14
7 Principle of measurement using the 3D anechoic void phantom . 15
7.1 General . 15
7.2 Analysis . 15
Annex A (informative) Description of construction of an example phantom and test
results . 17
Annex B (informative) System description . 37
Annex C (informative) Rationale . 38
Annex D (informative) Uniformity measurement . 41
Bibliography . 48

Figure A.1 – Example of measurement test equipment . 17
Figure A.2a) – Package of TMM slices containing alternating void slices and
attenuation slices of polyurethane foam . 19
Figure A.2b) – Holes of different diameters in the void slices allow the use of the
phantom with different ultrasound frequencies (1 – 15 MHz) . 19
Figure A.2 – TMM slices . 19
Figure A.3 – Structure of foam . 19
Figure A.4 – C-images of voids . 20
Figure A.5 – Experimental confirmation of Rayleigh distribution with attenuating TMM . 21
Figure A.6 – Speed of sound in saltwater . 22
Figure A.7 – Phantom with motor drive and two types of adapters . 22
Figure A.8 – B-, D-, C- images and grey scale . 24
Figure A.9 – Illustration of the VDR calculation for a ROI consisting of a single line . 25
Figure A.10 – B-C-D planes . 26
Figure A.11 – Principle of the ultrasound scanning array and beam . 27
Figure A.12 – Schematic of B-D-C planes . 28

TS 62558  IEC:2011(E) – 3 –
Figure A.13 – 3D-Phantom images . 29
Figure A.14 – B-D-C images and VDR . 30
Figure A.15a) – Example: Curved Array, 40-mm radius, 3,5MHz with good VDR-values. . 31
Figure A.15b) – Example: Curved Array, 40-mm radius, 3,5MHz with poor VDR-values . 31
Figure A.15 – VDR-values . 31
Figure A.16 – Example: Linear array transducer 13 MHz . 32
Figure A.17 – Interpretation of VDR parameter . 33
Figure A.18 – Explanation of saturation (0-255 grey-scale range) . 34
Figure A.19a) – Voids 2,5 mm . 35
Figure A.19b) – Voids 3,0 mm . 35
Figure A.19c) – Voids 4 ;0 mm . 35
Figure A.19 – Saturation effect . 35
Figure A.20 – Void spot analysis . 35
Figure A.21a) – Local dynamic curve . 36
Figure A.21b) – Expected envelope of VDR . 36
Figure 21 – Local dynamic range . 36
Figure C.1 – Autocorrelation function . 39
Figure C.2a) – Autocorrelation function at 4,06 cm depth . 40
Figure C.2b) – Autocorrelation function at 9,08 cm depth . 40
Figure C.2 – Autocorrelation function – dependence on depth . 40
Figure C.3 – Autocorrelation function at 10,94 cm depth . 40
Figure D.1a) – Uniformity test with related linear or curved array transducer . 42
Figure D.1b) – Fixed pattern in B-image . 42
Figure D.1 – Uniformity test . 42
Figure D.2a) – B-D-C image and fixed pattern in C-image . 43
Figure D.2b) – Grey scale display of full array . 43
Figure D.2 – Uniformity test – Additional features . 43
Figure D.3 – Linear transducer with reference tape . 44
Figure D.4 – Interpretation of simulated transducer failure when half of the probe is
covered by five layers of 50-mm fabric tape . 45
Figure D.5 – Disconnected elements, example with linear transducer . 46
Figure D.6 – Example with curved array transducer and reference tape . 47

– 4 – TS 62558  IEC:2011(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – REAL-TIME PULSE-ECHO SCANNERS –
PHANTOM WITH CYLINDRICAL, ARTIFICIAL CYSTS IN TISSUE-MIMICKING
MATERIAL AND METHOD FOR EVALUATION AND PERIODIC TESTING
OF 3D-DISTRIBUTIONS OF VOID-DETECTABILITY RATIO (VDR)

FOREWORD
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The main task of IEC technical committees is to prepare International Standards. In
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future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62558, which is a technical specification, has been prepared by IEC technical committee
87: Ultrasonics.
TS 62558  IEC:2011(E) – 5 –
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
87/434/DTS 87/458/RVC
Full information on the voting for the approval of this technical specification 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.
The committee has decided that the contents of this publication will remain unchanged until
the stability 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
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – TS 62558  IEC:2011(E)
INTRODUCTION
This technical specification provides an example of a measurement method and of a test
phantom. The specified method and test equipment permit operation without knowledge of
proprietary information of the diagnostic ultrasonic equipment manufacturer.
This technical specification describes desirable specifications and performance
characteristics of a tissue-mimicking material (TMM) 3D artificial-cyst phantom. An example
including design of a realized and conforming phantom is given. The described results are
independent of applied electronic and design architecture of diagnostic ultrasound systems
and related transducers suitable for testing with the phantom.
Medical diagnostic ultrasound systems and related transducers need periodic testing as the
quality of medical decisions based on ultrasonic images may decrease over time due to
progressive degradation of essential systems characteristics. The TMM phantom is intended
to be used to measure and to enable documentation of changes in void-detectability ratio in
periodic tests over years of use.
The example of phantom design uses sliced TMM arranged as alternating "cyst-slices" and
"attenuation-slices". It allows measurement along all three axes of the ultrasonic beam (axial,
azimuthal and elevation) to determine the void-detectability ratio depending on the depth in
the image generated from a transducer. The basis of the design concept and measurement
method is anechoic, artificial cysts, representing idealized pancreatic ducts in the human
body, and the measurement of the void-detectability ratio inside the images of these artificial
cysts. The images of the artificial cysts should appear anechoic. The measurement of void-
detectability ratio quantifies the diagnostic ultrasound system’s ability to properly represent
these objects. Increased artifactual signals appearing within images of these artificial cysts
indicate a degradation of certain image parameters. A certain level of artifactual signals is to
be expected for any ultrasound system, due to the emitted beam's shape and the transducer's
receive characteristics. Any increase in these artifactual signals may be caused, for example,
by grating- and side-lobes that may occur due to, for example, partial or total depolarisation of
elements, delamination between transducer elements and lens, or corrosion. The
measurement procedure allows a reliably and reproducible determination of the visibility limits
of small voids, an important image parameter of an ultrasound diagnostic system over the
time of use, by applying dedicated acquisition, processing and documentation software.
Four informative annexes are provided: Annex A – Description of construction of an example
phantom and test results; Annex B – System description; Annex C – Rationale; Annex D –
Uniformity measurement.
TS 62558  IEC:2011(E) – 7 –
ULTRASONICS – REAL-TIME PULSE-ECHO SCANNERS –
PHANTOM WITH CYLINDRICAL, ARTIFICIAL CYSTS IN TISSUE-MIMICKING
MATERIAL AND METHOD FOR EVALUATION AND PERIODIC TESTING
OF 3D-DISTRIBUTIONS OF VOID-DETECTABILITY RATIO (VDR)

1 Scope
This technical specification specifies essential characteristics of a phantom and method for
the measurement of void-detectability ratio for medical ultrasound systems and related
transducers. It is restricted to the aspect of long-term reproducibility of testing results.
This technical specification establishes:
– important characteristics and requirements for a TMM 3D artificial cyst phantom using
anechoic voids;
– a design example of a 3D artificial cyst phantom, the necessary test equipment and use of
relevant computer software algorithms.
This technical specification is currently applicable for linear array transducers. A uniformity
test prior to void-detectability ratio (VDR) measurement is recommended.
NOTE The basic concept of the 3D artificial-cyst phantom may also be valid for other types of ultrasound
transducers; however there is a need for further verification (see Annex D).
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 amendments) applies.
IEC 60050-802, International Electrotechnical Vocabulary, Part 802: Ultrasonics
3 Terms and definitions
For the purposes of this document, the terms and definitions contained in IEC 60050-802 as
well as the following terms and definitions apply.
3.1
acoustic coupling medium
medium, usually fluid or a gel, that allows echo-free coupling of the transducer to the coupling
window of the phantom.
3.2
artifactual signal
signal at a specific region in an image where no signal is expected (e.g. inside the image of a
void)
3.3
attenuation coefficient
at a specified frequency, the fractional decrease in plane wave amplitude per unit path length
in the medium, specified for one-way propagation

– 8 – TS 62558  IEC:2011(E)
–1 –1
Units: m (attenuation coefficient is expressed in dB m by multiplying the fractional
decrease by 8,686 dB)
[IEC 61391-2:2010, definition 3.4]
3.4
backscatter coefficient
at a specified frequency, the mean acoustic power scattered by a specified object in the 180°
direction with respect to the direction of the incident beam, per unit solid angle per unit
volume, divided by the incident beam intensity, the mean power being obtained from different
spatial realizations of the scattering volume
–1 –1
steradian
Units: m
NOTE The frequency dependency should be addressed at places where backscatter coefficient is used, if
frequency influences results significantly.
[IEC 61391-1:2006, definition 3.6, modified]
3.5
backscatter contrast
ratio between the backscatter coefficients of two objects or regions
[IEC 61391-2:2010, definition 3.8]
NOTE Backscatter contrast can be frequency-dependent but it is independent of any image system.
3.6
B-, C-, D-image
basic cross sectional presentations of 3D-images:
B-image is in a plane that is created by the acoustic scan-lines (scan plane);
C-image is in a plane perpendicular to the acoustic scan lines in the B-image;
D-image is in a plane perpendicular to B-image–plane and C-image-plane
3.7
B-, C-, D-(image) plane
B-plane: scan plane;
C-plane: reconstructed image plane that is perpendicular to acoustic scan lines in the B-
plane;
D-plane: reconstructed image plane that is perpendicular to the scan plane and the C-plane
3.8
coupling window
portion of the phantom’s enclosure provided for entrance and exit of the transmitted
ultrasound waves to/from the tissue-mimicking material without significant attenuation or
distortion
NOTE The coupling window usually consists of a thin membrane which protects the tissue-mimicking material
from evaporation, leakage and mechanical damage by the transducer and which does not significantly alter the
ultrasound signals
3.9
detection limit
smallest true value of the measurement, which is detectable by the measuring method
[IEC 60761-1:2002, definition 3.10, modified]

TS 62558  IEC:2011(E) – 9 –
3.10
digitized image data
two-dimensional or three-dimensional set of pixel (voxel) values derived from the grey-level
values of the B-mode images that are sent to the monitor screen
3.11
documentation
human-readable information about a device instance
[IEC 62453-1:2009, definition 3.1.18]
NOTE Within the context of this TS, the printed documentation and the documentation provided via Extended
Markup Language (XML) are also meant. The documentation can consist of several documents and images.
3.12
fixed pattern
parts of the B-mode image that remain in the same position relative to the image frame when
the transducer is moved
3.13
grey-level value
number determining the brightness of the pixels of a B-mode image (as derived from the
signal amplitude of the signal reflected from the corresponding position in the body)
NOTE The grey level values determine the brightness of specific pixels in the image and they historically range
from 0 (black) to 255 (white). Black indicates a weak signal, white a strong signal, This convention holds
throughout this document for calculations. In images an inverted display can be used, where black
indicates the level 256 and white 0.
3.14
(acoustic) scan line
one of the component lines that form a B-mode image on an ultrasound system monitor,
where each line is the envelope-detected A-scan line in which the echo amplitudes are
converted to brightness values
[IEC 61391-1:2006, definition 3.26, modified]
3.15
scan plane
acquired image plane containing the acoustic scan lines
[IEC 61391-2:2010, definition 3.30]
3.16
specific attenuation coefficient
at a specified frequency, the slope of attenuation coefficient plotted against frequency
–1 –1
Units: m Hz
3.17
Tissue-mimicking material
TMM
material in which the propagation velocity (speed of sound), reflection, scattering, and
attenuation properties are similar to those of soft tissue for ultrasound in the frequency range
1 MHz to 15 MHz
[IEC 61391-1:2006, 3.36, modified]

– 10 – TS 62558  IEC:2011(E)
3.18
TMM 3D artificial anechoic cyst phantom
phantom containing tissue-mimicking material, in which there are well-defined regions whose
backscatter contrast is lower than -60 dB relative to the regions containing TMM
3.19
uniformity test procedure
procedure to test the uniformity of the transmitted signals of all the elements of array
transducers
3.20
void
artificial anechoic cyst
region of defined geometry in a tissue-mimicking material that generates no scattered
acoustic waves
NOTE Saline solution in specified concentration is known to produce extremely low levels of scattered signals and
therefore it is an optimal approximation to a perfect void.
3.21
void-detectability ratio
VDR
number characterizing the visibility of an image area corresponding to a void of defined
diameter surrounded by tissue-mimicking material (TMM) in the phantom
VDR = (µ - µ ) / σ = (1/n)(Σ (VDR ))
1 2 1 i=1.n i
where
µ = mean image pixel value of the TMM in the region surrounding the void for a given
C-plane;
µ = mean value of the image pixel values from within the image area representing a void;
σ = standard deviation of mean pixel values over separate TMM areas equal to the void
area and lying in the region of the void, for a given C-plane;
n = number of voxels (pixels) from a given C-plane or from a specific part of this C-plane
(e.g. the image area of a single void or the image area of all voids within the C-plane)
NOTE 1 The image of the surrounding TMM material is expected to show modulated grey levels (i.e. an
ultrasound speckle image) due to the ultrasound interference patterns).
NOTE 2: The VDR formula is derived from [4]
3.21.1
detectability ratio for a single voxel
detectability ratio for a single voxel is defined by:
VDR = (µ - g ) / σ
i 1 i 1
where
µ = mean image pixel value of the TMM in the region surrounding the void for a given C-
plane;
g = grey level value of the i-th voxel (pixel) from a given C-plane or from a specific part of
i
this C-plane (e.g. the image area of a single void or the image area of all voids within
the C-plane);
σ = standard deviation of mean pixel values over separate TMM areas equal to the void
area and lying in the region of the void, for a given C-plane
___________
Numbers in square brackets refer to the Bibliography.

TS 62558  IEC:2011(E) – 11 –
NOTE The VDR formula is derived from [4].
3.21.2
maximum VDR within a void
VDR
v
maximum VDR within a void is defined by
VDR = (µ - g ) / σ = max (VDR )

v 1 v 1 i=1.n i
where
µ = mean image pixel value of the TMM in the region surrounding the void for a given
C-plane;
g = minimum grey-level value of the image region corresponding to the interior of a void;

v
σ = standard deviation of mean pixel values over separate TMM areas equal to the void
area and lying in the region of the void, for a given C-plane
NOTE The VDR formula is derived from [4].
maximum VDR in a ROI in a C-plane
VDR(max)
maximum value of VDR in a specified region of interest (ROI) within a C-plane
3.21.3
absolute maximum VDR in a ROI in a volume
VDR
absmax
absolute maximum value of all VDR -values in a volume comprising the evaluated region of
i
interest (ROI), i.e. in a display of the function VDR(max) over the total depth z in the evaluated

ROI
3.22
VDR limit
minimum value of the VDR for which there is visualization of a void on an ultrasound image
NOTE In [4] the detection limit for the detection of voids of the defined void sizes (see A.10.1) for a noise level
independent of electronic noise was stated to be around VDR = 2,5 for spherical voids.
4 Symbols
c = speed of sound
g = grey level value of the i-th voxel (pixel) from a given C-plane or from a

i…
specific part of this C-plane (e.g. the image area of a single void or the image
area of all voids within the C-plane)
g = minimum grey-level value of image region corresponding to the interior of a
v
void
T = temperature
S = salinity
S = maximum value of the digitized image data (grey-level values)
g max
VDR = void detectability ratio -- averaged value over the image of a void
VDR = detectability ratio for a single voxel (pixel) i, measured over a region in the
i
digitized image data
VDR = void detectability ratio -- maximum value within the image of a void
v
VDR(max) = maximum value of VDR in a specified ROI in a C-plane

= absolute maximum value of VDR in a display of the functional range of
VDR
absmax
VDR(max) over depth
– 12 – TS 62558  IEC:2011(E)
z = depth
µ = mean image pixel value of the TMM in the region surrounding the void for a
given C-plane
µ = mean value of the image pixel values from within the image area representing
a void
µ = mean value of the image pixel values from a 3D region of interest (ROI)
σ = standard deviation of mean pixel values over separate TMM areas equal to
the void area and lying in the region of the void, for a given C-plane
5 Ambient conditions of measurement with the phantom
Typical ambient conditions during measurements should be similar to those specified in
IEC 61319-1 and IEC 61319-2:
Temperature: 20 °C to 24 °C;
Relative humidity: 45 % to 75 %;
Atmospheric pressure: 86 kPa to 106 kPa.
6 Specification of TMM 3D artificial anechoic-cyst phantom
6.1 3D-phantom concept
The 3D phantom shall be composed of TMM that contains an arrangement of voids of a
specified shape (i.e. cylindrical) and sizes specified in relation to the defined frequency range
of transducers to be tested.
NOTE An example of a phantom that conforms to this technical specification is presented in Annex A.
6.2 General phantom specification
The phantom shall allow implementing the test procedures described in this document by
providing anechoic targets at known locations within tissue-mimicking material. Analysis of
images is done from digitized image data that are acquired during scans of the phantom. The
manufacturer shall provide an instruction manual with advice regarding reliable use and
maintenance.
6.3 TMM specifications:
The following parameters of the TMM shall lie within the specified limits:
–1
Speed of sound: (1 540 ± 10) m s at 3 MHz
–3
Density: (1,00 ± 0,11) g cm
–1 –1
Specific attenuation coefficient: (0,7 + 0,2/ - 0,05) dB cm MHz in the 1 MHz to 15 MHz
range. If a phantom is manufactured by using layered materials as in Annex A, for example,
the specific attenuation coefficient corresponding to the mean value of the specific attenuation
shall apply.
–4 –1 –1
Backscatter coefficient: (3 × 10 cm sr ) ± 10 dB at 3 MHz; with a “frequency to the n”
n
(f ) dependence, where 2 < n < 4 from 1 MHz to 15 MHz. The value of the backscatter
coefficient of the phantom shall be reported as a function of frequency, together with the
results obtained with the phantom. Scatterers within the phantom should be of a sufficient
number density to provide Rayleigh statistics in the echo-amplitude distribution (see Figure
A.2.2). The scatterer number density needed will depend on the frequency and focusing
characteristics of the transducer and ultrasound system to be tested under this technical

TS 62558  IEC:2011(E) – 13 –
specification. For guidance, around 10 scatterers per cubic millimetre are sufficient for most
transducers operating up to 15 MHz.
Phantoms manufactured to these TMM specifications can be constructed using, for example,
open pore sponges or polyurethane foam immersed in saline. The materials have microscopic
inhomogeneities that are uniformly distributed throughout to produce the desired attenuation
level.
6.4 Anechoic targets
Anechoic targets shall be provided whose backscatter contrast is at least -60 dB relative to
that of the background TMM material. Degassed saline solution is an adequate material for
filling anechoic targets. The saline shall be adapted in concentration to achieve sound speed
–1
of (1 540 ± 10) m s . The sound speeds in saltwater as a function of saline concentration and
temperature is shown Figure A.2.3.
Anechoic targets shall be placed at different depths throughout the phantom volume. Targets
of a given diameter shall be positioned with their centres coplanar, so that in the scan plane
at least 6 such targets are viewed at different lateral locations at each depth from the
transducer. Targets shall be positioned in lateral locations so that they can be viewed from
different locations within the scanning plane. Targets in the phantom presented in Annex A
are cylinders whose faces are parallel to the scanning surface.
At each depth and lateral location, various sizes of anechoic targets shall be available. For
each frequency region two sizes of voids shall be present. Dimensions of voids shall be
selected in regard to realistic azimuthal and elevational beam width and frequency of the
transducer, as follows:
– Voids of 4 mm and 2,5 mm diameter are satisfactory for transducers operating in the
1 MHz to 4 MHz range.
– Voids of 3 mm and 1,5 mm diameter are satisfactory for transducers operating in the
4 MHz to 8 MHz range
– Voids of 2,5 mm and 1 mm diameter are satisfactory for transducers operating in the
8 MHz to 15 MHz range
One important reason for the occurrence of artifactual signals inside of anechoic voids are
side-lobes of the ultrasonic beam [9], A prerequisite to detect artifactual signals caused
by side-lobes and/or grating-lobes in images of anechoic voids is an echo-amplitude
difference better than -60 dB compared to the surrounding tissue-mimicking material.
6.5 Phantom enclosure
The purpose of this enclosure is to protect the contents from degradation (fluid evaporation)
with time during use and storage. The material used for the enclosure walls shall be such as
to prevent degradation of the contents.
6.6 Scanning surface
The scanning surface shall allow acoustic contact of the entire active surface of the
transducer with the phantom. If the scanning surface includes a window material, such as a
foil or membrane, to prevent desiccation of the TMM or to protect the TMM contents from
damage from the transducer, the membrane properties, including material contained therein,
thickness, density, and specific attenuation coefficient, shall be provided. Alternatively,
transmission losses as a function of frequency shall be provided.
6.7 Dimensions
The dimensions of the phantom shall be suitable to evaluate transducers by assessing VDR at
least 2/3 of the imaged field for which the transducer is typically used. For example, a

– 14 – TS 62558  IEC:2011(E)
ultrasound system that provides a 24 cm imaging depth requires a phantom of at least 16 cm
depth. This is generally at least four times the size of the transducer transmit-receive
aperture, so any degradation caused by side lobes or by poor lateral resolution would be
manifested within this range.
6.8 Phantom stability
The manufacturer shall state the duration of stability and indicate criterion of use.
6.9 Digitized image data
Test and analysis methods described in this technical specification are applied to digitized
image data derived from the ultrasound system and related transducer being evaluated. In all
cases, grey level values for all spatial locations in the image must be available. Image data
typically are in a matrix consisting of about 300 × 300 pixels and at least 8 bits (256 levels) of
amplitude (directly proportional to grey-scale) resolution.
Digitized image data may be obtained using a video frame grabber to digitize images from
output connectors normally used to transfer images to analogue monitors or to recording
devices. The video signal digitization must be provided under exactly specified conditions to
avoid or minimize signal distortions. Specific care and attention shall be taken for the
following parameters:
– The input dynamic range of the video-frame grabber shall be adjusted according to the
maximum signal amplitude of the video output.
– The digitizing amplitude resolution (given by the pixel byte size) shall be better than
that of the grey-scale resolution of the ultrasound image video-output signal. A
minimum of 8 bits or 256 grey levels is required.
– Ultrasound image signal to TV conversion-function linearity has to be assured. The
spatial resolution (given by the voxel size) of the digital picture must be better than the
original video line density of the image.
– The video-capture frame rate of the video-frame grabber must be high enough to allow
acquisition of data to keep up with input data rates, if the imaged field is moved. Keep
in mind the difference between scanning frame rate and output video frame rate.
– A cable matched for input/output impedance has to be used to avoid reflections in the
line. A cable length of 1 m to 2 m is generally not critical.
– The digitized image data must be representative of those on the display monitor of the
diagnostic ultrasound system. The digitized image data derived from the diagnostic
ultrasound system shall not undergo any post-processing modifications between the
point of data processing and the monitor output signal of the system before being
subjected to analysis as described in this technical specification.
Data also can be acquired using DICOM-images (Digital Imaging and Communications in
Medicine) [13] or images in other formats from the ultrasound system. This method is used by
most ultrasound system manufacturers for in-house quality-control testing and image-
processing development. Capabilities often exist to extend the method for use by clinical
personnel using, for example, file-transfer-protocol (ftp) resources.
Alternatively, many diagnostic ultrasound systems provide image files on removable media,
such as USB-thumb drives, magneto-optical disks, zip disks, or CD-ROM, and these are
appropriate sources of digital images data as well.
In addition, many imaging centres use commercially available Picture Archiving and
Communication Systems (PACS) for viewing and storing ultrasound-image data.
Manufacturers of PACS systems usually provide means to acquire images in an
uncompressed format, such as a tiff (Tagged Image File Format) or a DICOM format, to
workstations that have access rights to the image data.

TS 62558  IEC:2011(E) – 15 –
In any case, where image data are not acquired from the (analogue or digital) video output but
from data derived within the ultrasound system, it must be ascertained that the digitized
amplitude provided in this case really corresponds to the grey-levels shown on the viewing
screen.
Until DICOM offers a standard for 3D-images the best procedure is to use a VGA or DVI
converter to digitize the video output signal of the ultrasound system.
7 Principle of measurement using the 3D anechoic void phantom
7.1 General
The measurement equipment for the VDR measurement consists of the phantom, the
transducer and ultrasound system to be tested, and a means to acquire digitized image data
from scan planes that extend over that volume of the phantom that contains voids.
An acceptable method for acquiring the 3D data is to apply the mechanical transducer
positioner described in Annex A, then to record digitized image data from closely positioned
scan planes. The scan plane spacing should be equal to the voxel separation within the scan-
planes, however; it should be less than 1/4 times the diameter of the void from which VDR will
be computed.
Other approaches to 3D data acquisition are to use special transducers, such as those with
built-in mechanical translation of the probe, or to use manual translation of the transducer
while recording image data in a cine image loop, such as those provided within the ultrasound
system. However, the latter approach does not allow for ensuring an appropriate B-plane
spacing.
A uniformity measurement of transducers is essential. It should be done prior to VDR
measurement. One possible method is described in Annex D.
7.2 Analysis
The following is an acceptable method of analysis:
VDR is computed for anechoic targets (i.e., voids) of a given diameter, depth, and lateral
location in planes parallel to accessible C-planes, as described in Annex A. However, for this
technical specification, results shall be reported for C-planes containing voids.
Within images reconstructed from the acquired 3D data a region of interest (ROI) is defined.
The data in this region shall provide cubic voxels (i.e. the dimensions of the voxel should be
identical in all three directions) of known size. To achieve this objective, information on the
image scale must be acquired. The 3D-ROI data are stored in a matrix to allow viewing and
processing of this 3D-data set.
For each C-plane within the 3D-ROI the mean (µ ) and the standard deviation (σ ) values for
1 1
the TMM are calculated. Di
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