IEC TS 62791:2022

IEC TS 62791 ®
Edition 2.0 2022-07
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Pulse-echo scanners – Low-echo sphere phantoms and method
for performance testing of grey-scale medical ultrasound scanners applicable to
a broad range of transducer types

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IEC TS 62791 ®
Edition 2.0 2022-07
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Pulse-echo scanners – Low-echo sphere phantoms and method

for performance testing of grey-scale medical ultrasound scanners applicable to

a broad range of transducer types

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 11.040.50; 17.140.50 ISBN 978-2-8322-3922-3

– 2 – IEC TS 62791:2022 © IEC 2022
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 11
4 Symbols . 15
5 General and environmental conditions . 16
6 Equipment required . 17
6.1 General . 17
6.2 Phantom geometries . 17
6.2.1 Low-contrast phantoms for assessing the ability to delineate tumour
boundaries . 17
6.2.2 High-contrast phantoms to evaluate scanner performance, tune scanner
pre-sets, and detect defects in probes . 18
6.2.3 Total internal reflection surfaces . 19
6.2.4 Spatially random distribution of low-echo spheres. 19
6.3 Ultrasonic properties of the tissue-mimicking (TM) phantoms . 19
7 Data acquisition assuming a spatially random distribution of low-echo spheres . 20
7.1 Methodology . 20
7.1.1 General . 20
7.1.2 Mechanical translation . 20
7.1.3 Manual translation with cine-loop recording . 21
7.2 Storage of digitized image data . 22
7.3 Digital image files available from the scanner itself . 23
7.4 Image archiving systems . 23
8 Automated data analysis for quantifying low-echo sphere detectability . 23
8.1 General . 23
8.2 Computation of mean pixel values (MPVs) . 23
8.3 Additional restrictions for sector images . 29
8.3.1 Convex arrays . 29
8.3.2 Phased arrays . 30
8.4 Determination of the LSNR -value for a given depth interval . 30
m
8.4.1 Preliminaries . 30
8.4.2 Computation of LSNR for depth interval label d . 31
md
8.4.3 Standard error corresponding to each LSNR -value . 31
md
9 Visual assessments of images . 31
9.1 Image comparisons . 31
9.2 Semi-quantitative image analysis . 32
Annex A (informative) Example of a phantom for performance testing in the 1 MHz to
7 MHz frequency range . 34
Annex B (informative) Illustrations of the computation of LSNR -values as a function
md
of depth . 36
Annex C (informative) Sufficient number of data images to assure reproducibility of
results . 43
C.1 General . 43

C.2 Phantom with 3,2-mm-diameter, −20 dB low-echo sphere, having two
spheres per millilitre . 43
C.3 Phantom with 2-mm-diameter, −20 dB spheres and eight spheres per
millilitre . 48
Annex D (informative) Example of a phantom for performance testing in the 7 MHz to

23 MHz frequency range . 52
Annex E (informative) Determination of low-echo sphere positions to within D/8 in x-,
y- and z-Cartesian coordinates . 54
E.1 Procedure . 54
E.2 Argument for the choice of seven MPV nearest-neighbour sites for
determining the centres of low-echo spheres . 56
Annex F (informative) Tests of total internal reflection produced by alumina and plate-
glass, plane reflectors . 57
Annex G (informative) Results of a test of reproducibility of LSNR as a function of
md
depth for a phantom with 4-mm-diameter, −20 dB spheres, having two spheres per
millilitre . 64
Annex H (informative) Results for low-echo sphere concentration dependence of
LSNR as a function of depth for phantoms with 3,2-mm-diameter, −20 dB spheres . 66
md
Annex I (informative) Comparison of two different makes of scanner with similar
transducers and console settings . 70
Annex J (informative) Special considerations for 3-D probes . 72
J.1 3-D probes operating in 2-D imaging mode . 72
J.2 2-D arrays operating in 3-D imaging mode for determining LSNR -values as
md
a function of depth for reconstructed images . 72
J.3 Mechanically driven 3-D probes operating in 3-D imaging mode . 72
Bibliography . 73

Figure 1 – Flow chart . 22
Figure 2 – Schematic of the image plane nearest to the nth low-echo sphere and not
influenced by the presence of an image boundary . 25
Figure 3 – Modification of Figure 2 showing a vertical image boundary (solid line) and
a parallel dashed line, between which (MPV) values are excluded from computation
ijk
of S or σ in Formula (2) . 26
mBn Bn
Figure 4 – Limiting case of Figure 3 where the vertical image boundary is tangent to
the imaged low-echo sphere . 27
Figure 5 – Modification of Figure 2 showing a 45° sector image boundary (solid line)
and a parallel dashed line, between which (MPV) values are excluded from
ijk
computation of S or σ in Formula (2) . 28
mBn Bn
Figure 6 – Limiting case of Figure 5 where the 45° sector image boundary is tangent to
the imaged low-echo sphere . 29
Figure 7 – Usefulness of simple visual inspection of images of a standardized low-echo
sphere phantom . 32
Figure 8 – Zones over which at least half of the spheres appear clearly outlined as a
nearly full-size circle and are free of echoes (Zone 1) or an average of more than one
sphere per slice can be discerned (Zone 2) . 33
Figure A.1 – End view of the phantom applicable for 1 MHz to 7 MHz showing the
spatially random distribution of 3,2-mm-diameter, −6 dB spheres . 34
Figure A.2 – Top view of phantom with 3,2-mm-diameter, −6 dB spheres . 35
Figure B.1 – Convex-array image of a prototype 4-mm-diameter, −20 dB sphere
phantom for use in the 1 MHz to 7 MHz frequency range . 36

– 4 – IEC TS 62791:2022 © IEC 2022
Figure B.2 – Auxiliary figures relating to Figure B.1 . 37
Figure B.3 – Results corresponding to Figure B.1 and Figure B.2, demonstrating
reproducibility . 38
Figure B.4 – Results corresponding to Figure B.1, Figure B.2 and Figure B.3 . 39
Figure B.5 – One of 80 parallel, linear-array images of the phantom containing
4-mm-diameter, −20 dB spheres, imaged at 4 MHz with the transmit focus at 3 cm
depth . 39
Figure B.6 – Three successive images of the set of 80 frames addressed in Figure B.5,
where imaging planes were separated by D/4 equal to 1 mm . 40
Figure B.7 – Results for the 4-cm-wide, 3-cm-focus, linear array addressed in
Figure B.5 and Figure B.6 using all 80 image frames in two sets . 41
Figure B.8 – Results for the 4-cm-wide, 3-cm-focus, linear array addressed in
Figure B.5, Figure B.6 and Figure B.7, using all 80 image frames corresponding to
Figure B.7 in one set . 42
Figure C.1 – One image obtained from a phantom containing 3,2-mm-diameter, −20 dB

spheres by using a 4 MHz linear array focused at 3 cm depth . 43
Figure C.2 – Reproducibility result for two independent sets of 70 images with a mean
number of low-echo sphere centres that is about 15 per 5 mm-depth interval . 44
Figure C.3 – Results obtained by combining both sets of 70 independent images
corresponding to Figure C.2 into a single, 140-image set . 45
Figure C.4 – Sector image (curved array) at 4,5 MHz with multiple transmit foci at

4 cm, 8 cm and 12 cm depths; the −20 dB spheres are 3,2 mm in diameter . 45
Figure C.5 – Reproducibility results for a multiple transmit-focus (4 cm, 8 cm and
12 cm) case corresponding to Figure C.4 . 46
Figure C.6 – Reproducibility results for the case corresponding to Figure C.5, except
that there is a single focus at a 10 cm depth . 47
Figure C.7 – Reproducibility results for the case corresponding to Figure C.5, except

that there is a single transmit focus at 4 cm depth . 47
Figure C.8 – Image of a phantom containing 2-mm-diameter, −20 dB spheres, made
with a curved array having a 1,5 cm radius of curvature, with its transmit focus at 3 cm
depth . 48
Figure C.9 – Reproducibility results corresponding to Figure C.8 . 49
Figure C.10 – Results using all 100 images in the image set that gave rise to

Figure C.9 . 49
Figure C.11 – Image of a phantom containing 2-mm-diameter, −20 dB spheres, made
with a high-frequency (15 MHz) linear array and a transmit focus of 4 cm depth . 50
Figure C.12 – Reproducibility results corresponding to Figure C.11 . 51
Figure C.13 – Results using all 200 images in the image set that gave rise to
Figure C.12 . 51
Figure D.1 – End- and top-view diagrams of the phantom containing 2-mm-diameter,
low-echo spheres with a backscatter level −20 dB relative to the background, for use in
the 7 MHz to 23 MHz frequency range . 52
Figure D.2 – Image of the phantom containing 2-mm-diameter, −20 dB spheres [7], [8]
obtained with a paediatric transducer with a radius of curvature of about 1,5 cm . 53
Figure E.1 – Diagram discussed in the second paragraph of 3) . 54
Figure F.1 – Average of 10 images obtained by using a phased array transducer . 58
Figure F.2 – Mean and standard deviation of pixel value plotted against depth from the

two rectangular regions seen in Figure F.1 . 59
Figure F.3 – Same as Figure F.2, but for data obtained after the transducer was
rotated 180°, so the plate-glass reflector appeared on the right side of the image . 59

Figure F.4 – The percentage by which the mean pixel values resulting from reflections
differ from the mean pixel values not involving reflections plotted against depth . 60
Figure F.5 – Image obtained using a wide-sector (153°), 1 cm radius-of-curvature

transducer . 61
Figure F.6 – Mean pixel value and its standard deviation plotted against depth from the
two rectangular regions in Figure F.5 . 61
Figure F.7 – Same as Figure F.6, only the transducer was rotated 180°, so the alumina
reflector was on the right side of the B-mode image . 62
Figure F.8 – The percentage by which the mean pixel values resulting from reflections

differ from the mean pixel values not involving reflections . 63
Figure G.1 – Example image of the phantom, taken with a 4,2 MHz curved array . 64
Figure G.2 – Reproducibility results corresponding to the two 40-image data subsets,
one of which is shown in Figure G.1 . 65
−1
Figure H.1 – Example of an image from the 75-image, 4 ml data set producing the
results shown in Figure H.2. 66
Figure H.2 – Results for the phantom containing four 3,2-mm-diameter, −20 dB low-
echo spheres per millilitre . 67
Figure H.3 – Example of an image from the 140-image, two spheres per millilitre data
set producing the results shown in Figure H.4 . 67
Figure H.4 – Results for the phantom containing two 3,2-mm-diameter, −20 dB low-
echo spheres per millilitre . 68
Figure H.5 – Example of an image from the 180-image, one sphere per millilitre data
set producing the results shown in Figure H.6 . 68
Figure H.6 – Results for the phantom containing one 3,2-mm-diameter, −20 dB low-
echo sphere per millilitre . 69
Figure I.1 – Results for System A scanner and 7CF2 3-D (swept convex array)
transducer focused at 4 cm depth and operated at 4,5 MHz in 2-D mode . 70
Figure I.2 – Results for System B scanner with a 4DC7-3 3-D (convex array)
transducer focused at 4 cm depth and operated at 4 MHz in 2-D mode . 71

– 6 – IEC TS 62791:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – PULSE-ECHO SCANNERS – LOW-ECHO
SPHERE PHANTOMS AND METHOD FOR PERFORMANCE
TESTING OF GREY-SCALE MEDICAL ULTRASOUND SCANNERS
APPLICABLE TO A BROAD RANGE OF TRANSDUCER TYPES

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
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6) All users should ensure that they have the latest edition of this publication.
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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.
IEC TS 62791 has been prepared by IEC technical committee 87: Ultrasonics. It is a Technical
Specification.
This second edition cancels and replaces the first edition published in 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition.
a) It introduces necessary corrections to the analysis methods; these have been published in
the literature.
b) It increases the range of contrast levels of low-echo spheres in phantoms that meet this
Technical Specification. Previous specification was -20 dB, but two additional levels, -6 dB
and either -30 dB or, if possible, -40 dB, are now specified.
c) It includes a wider range of uses of the methodology, including testing the effectiveness of
scanner pre-sets for specific clinical tasks and detecting flaws in transducers and in
beamforming.
d) It decreases the manufacturing cost by decreasing phantoms' dimensions and numbers of
low-echo, backscattering spheres embedded in each phantom.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
87/776/DTS 87/790A/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
Terms in bold in the text are defined in Clause 3.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document 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.

– 8 – IEC TS 62791:2022 © IEC 2022
INTRODUCTION
Ultrasonic pulse-echo scanners are widely used in medical practice to produce images of soft-
tissue organs throughout the human body. Most ultrasonic pulse-echo scanners produce real-
time images of tissue in a scan plane by sweeping a narrow, pulsed beam of ultrasound through
the tissue section of interest and detecting the echoes generated by reflection at tissue
boundaries and by scattering within tissues. Many newer scanners transmit broad, overlapping
ultrasound beams, and apply software beam-forming to synthesize narrow, pulse-echo beam
patterns.
Generally, the sweep that generates an image frame is repeated at least 20 times per second,
giving rise to the real-time aspect of the displayed image. The axes of the pulsed beams
generally lie in a plane that defines the scan plane.
Various transducer types are employed to operate in a transmit–receive mode to generate and
detect the ultrasonic signals. Linear arrays, in which the beam axes are all parallel to one
another, resulting in a rectangular image, consist of a line of hundreds of parallel transducer
elements with a subset of adjacent elements producing one pulse at a time. Convex arrays are
similar to linear arrays but the element arrangements define part of the surface of a short, right,
circular cylinder with the array elements parallel to the axis of the cylinder. The radius of
curvature of the cylinder (and therefore the array) can have values between 0,5 cm and 7 cm.
The convex array generates a sector image, since the beam axes fan out over the scan plane.
Some linear- and convex-array models, such as "1,25-D" arrays, incorporate multiple rows of
elements to provide additional control of the elevational beam width.
A phased array has a linear arrangement of elements, where all elements act together to form
a pulse and the direction and focus of an emitted pulse is determined by the timing of excitations
of the elements. The phased array generates a sector image. Another type of sector scanner is
the mechanical sector scanner in which a single-element transducer or an annular-array
transducer is rotated about a fixed axis during pulse emissions. The foregoing transducer types
commonly operate within the frequency range 1 MHz to 23 MHz, to which this document applies.
Medical ultrasound systems exist whose transducers operate at frequencies as high as 33 MHz.
Although the procedures specified in this document might be appropriate for these systems,
phantoms outlined in this document have not yet been described for use in the 23 MHz to
33 MHz frequency range.
A two-dimensional array (2-D array) is restricted to an array of transducer elements distributed
over a rectangular area or a spherical cap. Such an array receives echoes from a 3-D volume
and can produce images corresponding to any planar surface in that volume. A 3-D
mechanically driven, convex array (3-D MD convex array) means a convex array that acquires
images as it is rotated mechanically about an axis lying in its image plane or an extension of
that plane. A 3-D mechanically driven, linear array (3-D MD linear array) is similar to a 3-D MD
convex array, where the array radius of curvature is infinite and the array is either rotated about
an axis or is translated perpendicularly to the scan plane of the linear array. For an overview of
current 3-D and 4-D systems, see 1.5 and 10.2.2 of [1] .
One means for testing the imaging performance of an ultrasound pulse-echo scanner is to
quantify the degree to which a small (low-echo) sphere is distinguished from the surrounding
soft tissue, i.e. the degree to which a small, low-echo sphere is detectable in the surrounding
soft tissue. It is reasonable to assume that the smaller the low-echo sphere that can be
detected at some position, the better the resolution of the scanner, i.e. the better it will display
and delineate the boundary of an abnormal object, such as a tumour, and the more accurately
it will display local acoustic properties.
____________
Numbers in square brackets refer to the Bibliography.

There are three components of resolution defined in pulse-echo ultrasound:
– axial resolution (parallel to the local, pulse-propagation direction);
– lateral resolution (perpendicular to the local, pulse-propagation direction and parallel to the
scan plane); and
– elevational resolution (perpendicular to the local, pulse-propagation direction and also to
the scan plane).
Axial resolution usually – but not always – is better than lateral and elevational resolutions.
Thus, all three components affect an object's detectability. A sphere has no preferred
orientation and is therefore the best shape for assessing detectability of a low-echo object for
two reasons. First, all three components of resolution are weighted equally, no matter what the
beam's incident direction is. Second, the incident beam's propagation direction will vary
considerably in the case of convex and phased arrays depending on where the object exists in
the imaged volume.
Imaging performance can be reduced by:
• beam distortions associated with dead or weak elements in array transducers;
• side lobes and grating lobes that are present with some array transducers;
• unexpected beam changes accompanying variations in the transmit foci applied to multi-row
("1,25-D") arrays; and
• electronic noise.
All can contribute to artifactual echoes on clinical images and on images of phantoms containing
low-echo spheres or to erroneous echo-signal amplitudes.
It is important that the phantom allow quantification of detectability to be carried out over the
entire depth range imaged; thus, it is important that the low-echo spheres exist up to the entire
scanning window. A phantom limited to a flat scanning surface is acceptable for a linear array,
phased array or a flat 2-D array but not for the remaining types of arrays. Each of the phantoms
specified in this document contains a random distribution of equal diameter [2], low-echo
spheres existing at all depths, including the case of those designed for testing convex (curved)
arrays.
This document summarizes the requirements for a phantom to provide for determination of
detectability of small, low-echo spheres for any type of pulse-echo transducer, except
(perhaps) a 2-D array with a spherical-cap surface.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is claimed
that compliance with this document may involve the use of a patent. IEC takes no position
concerning the evidence, validity, and scope of this patent right.
The holder of this patent right has assured IEC that s/he/it is willing to negotiate licences under
reasonable and non-discriminatory terms and conditions with applicants throughout the world.
In this respect, the statement of the holder of this patent right is registered with IEC. Information
can be obtained from the patent database available at patents.iec.ch.
Attention is drawn to the possibility that some of the elements of this document may be the
subject of patent rights other than those in the patent database. IEC shall not be held
responsible for identifying any or all such patent rights.

– 10 – IEC TS 62791:2022 © IEC 2022
ULTRASONICS – PULSE-ECHO SCANNERS – LOW-ECHO
SPHERE PHANTOMS AND METHOD FOR PERFORMANCE
TESTING OF GREY-SCALE MEDICAL ULTRASOUND SCANNERS
APPLICABLE TO A BROAD RANGE OF TRANSDUCER TYPES

1 Scope
This document, which is a Technical Specification, defines terms and specifies methods for
quantifying detailed imaging performance of real-time, ultrasound B-mode scanners. Detail is
assessed by imaging phantoms containing small, low-echo spherical targets in a tissue-
mimicking background and analysing sphere detectability [3]. Specifications are given for
phantom properties. In addition, procedures are described for acquiring images, conducting
qualitative analysis of sphere detectability, and carrying out quantitative analysis by detecting
sphere locations and computing their contrast-to-noise ratios. With appropriate choices in
design, results can be applied, for example:
• to assess the relative ability of scanner configurations (scanner make and model, scan head
and console settings) to delineate the boundary of a tumour or identify specific features of
tumours;
• to choose scanner control settings, such as frequency or the number and location of transmit
foci, which maximize spatial resolution;
• to detect defects in probes causing enhanced sidelobes and spurious echoes.
The types of transducers used (see sections 7.6 and 10.7 of [1]) with these scanners include:
a) phased arrays,
b) linear arrays,
c) convex arrays,
d) mechanical sector scanners,
e) 3-D probes operating in 2-D imaging mode, and
f) 3-D probes operating in 3-D imaging mode for a limited number of sets of reconstructed 2-D
images.
The test methodology is applicable for transducers operating in the 1 MHz to 23 MHz frequency
range.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050-802, International Electrotechnical Vocabulary – Ultrasonics (available at:
http://www.electropedia.org)
IEC 61391-1, Ultrasonics – Pulse-echo scanners – Part 1: Techniques for calibrating spatial
measurement systems and measurement of system point-spread function response
IEC 61391-2:2010, Ultrasonics – Pulse-echo scanners – Part 2: Measurement of maximum
depth of penetration and local dynamic range

IEC TS 62736, Ultrasonics – Pulse-echo scanners – Simple methods for periodic testing to
verify stability of an imaging system's elementary performance
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-802,
IEC 61391-1, IEC 61391-2 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
active area of a transducer
area over which transducer transmitting and/or receiving elements are distributed
3.2
backscatter coefficient
intrinsic backscatter coefficient
η
intrinsic property of a material, at some frequency, equal to the differential scattering cross-
section per unit volume for a scattering angle of 180°
Note 1 to entry: See [4], [5], [6].
[SOURCE: IEC 61391-1:2006, 3.6, modified – The term "differential scattering cross-section"
is used in place of factors comprising this quantity that are included in the source definition.]
3.3
low-echo sphere
hypoechoic sphere
spherical inclusion in a phantom, with a backscatter coefficient that is lower than the
backscatter coefficient of the surrounding tissue-mimicking material
3.3.1
low-constrast, low-echo sphere
low-echo sphere with a backscatter coefficient that is 6 dB (±0,2 dB) lower than the
backscatter coefficient of the surrounding tissue-mimicking material
3.3.2
high-contrast, low-echo sphere
low-echo sphere with with a backscatter coefficient that is at least 30 dB lower than the
backscatter coefficient of the surrounding tissue-mimicking material
Note 1 to entry: See also 6.3.
3.4
sphere diameter
D
diameter of spherical inclusions in a phantom
Note 1 to entry: It is generally assumed that all low-echo spheres in a particular phantom have the same diameter
D.
– 12 – IEC TS 62791:2022 © IEC 2022
3.5
pixel
smallest spatial unit or cell size of a digitized two-dimensional array representation of an image
Note 1 to entry: Each pixel has an address corresponding to its position in the array.
Note 2 to entry: Pixel is a contraction of "picture element".
[SOURCE: IEC 61391-1:2006, 3.23, modified – Supplementary information has been moved
from the definition to Note 1 to entry; the words "and a specific brightness level" have been
deleted from the supplementary information.]
3.6
pixel value
integer value of a processed signal level or integer values of processed colour levels, provided
to the display for a given pixel
Note 1 to entry: In a grey-scale display the pixel value is converted to a luminance by some, usually monotonic,
M
function. The set of integer values representing the grey scale runs from 0 (black) to (2 − 1) (white), where M is a
positive integer, commonly called the bit depth. Thus, if M = 8, the largest pixel value in the set is 255.
3.7
digitized image data
two-dimensional set of pixel values derived from the ultrasound echo signals that form an
ultrasound image
3.8
mean pixel value
MPV
mean of pixel values detected over a designated area or volume in an image or 3D stack of
images. For low echo spheres here, MPV is defined for an area A in a phantom image, where A
is somewhat smaller than the area of a circle of diameter D
Note 1 to entry: The phrase "somewhat smaller than" is introduced as partial compensation for the partial volume
effect in the elevational dimension [3].
Note 2 to entry: The partial volume effect is a term common in computed tomography, magnetic resonance imaging,
and ultrasound imaging. This process refers to the effect of the finite imaging resolution, particularly the slice
thickness. The signal (pixel values) at points near the object boundaries will include contributions from that object
and contributions from the material around it. For example, if the object is a sphere with diameter close to the
thickness of the slice, then one cannot define a good measurement region in the image of the sphere in which the
signal does not include components from material lying outside the sphere.
3.9
depth interval
interval between boundaries of contiguous depth segments into which an image area is
subdivided for computation of LSNR -values as a function of depth
md
Note 1 to entry: A rectangular scan area will be subdivided into horizontal bands; a sector scan area will be
subdivided into annular ring segments, the angular limits being determined by the sector angle (see Figure B.2 d).
Rectilinear projection of these area segments in the elevational direction will create volume segments analogous to
slabs and partial cylindrical shells, respectively, with thickness equal to the depth interval extent ∆.
3.9.1
depth interval label
d
integer for identifying depth intervals in an image
Note 1 to entry: d = 1, 2, …, d where 1 is at the least depth and d is at the greatest depth.
max max
Note 2 to entry: In computations of the centre of the nth sphere cluster in Annex E, the correct value of d on the
right sides of Formulas (E.1), (E.2) and (E.3) depends on the specific i,j coordinates of each site, s, in the cluster.
When the cluster extends beyond a boundary of a depth interval into an adjacent volume segment, then d will be
incremented or decremented by 1 for those sites located in the adjacent volume segment.

3.9.2
depth interval extent
∆
extent of each equal segment into which an image area is subdivided for computation of LSNR -
m
values as a function of depth
Note 1 to entry: Depth interval extent is expressed in millimetres (mm).
Note 2 to entry: Experience determining LSNR -values for numerous cases has led to the conclusion that a 4-mm
m
value of ∆ is adequate for the phantoms containing 4,0 mm-diameter and 3,2 mm-diameter low-echo spheres, and
a 2-mm value of ∆ is adequate for the phantoms containing 2 mm-diameter low-echo spheres.
Note 3 to entry: The maximum image depth is the sum of a set of contiguous depth interval extents; thus, if the
imaging depth is 16 cm and each depth interval spans 4 mm = 0,4 cm, then there are 16/0,4 = 40 depth intervals.
Equivalently, the maximum image depth is the product of the maximum depth interval label, d , and the depth
max
interval extent ∆. The maximum image depth is d × ∆ = 40 × 0,4 = 16 cm in this example.
max
3.10
detectability
numerical val
...