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

IEC TS 62791:2022 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. 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 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.
IEC TS 62791:2022 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.

General Information

Status
Published
Publication Date
17-Jul-2022
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
18-Jul-2022
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IEC TS 62791:2022 - 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
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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
IEC TS 62791:2022-07(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 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

8.4.1 Preliminaries ................................................................................................. 30

8.4.2 Computation of LSNR for depth interval label d .......................................... 31

8.4.3 Standard error corresponding to each LSNR -value ..................................... 31

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

of depth ................................................................................................................................ 36

Annex C (informative) Sufficient number of data images to assure reproducibility of

results .................................................................................................................................. 43

C.1 General ................................................................................................................. 43

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IEC TS 62791:2022 © IEC 2022 – 3 –
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

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

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

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

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– 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

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IEC TS 62791:2022 © IEC 2022 – 5 –

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

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

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– 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

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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.
---------------------- Page: 8 ----------------------
IEC TS 62791:2022 © IEC 2022 – 7 –

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.
---------------------- Page: 9 ----------------------
– 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 addi
...

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