Ultrasonics - Pulse-echo scanners - Low-echo sphere phantoms and method for performance testing of gray-scale medical ultrasound scanners applicable to a broad range of transducer types

IEC TS 62791:2015(E) defines terms and specifies methods for quantifying the imaging performance of real-time, ultrasound B-mode scanners. The test methodology is applicable for transducers operating in the 2 MHz to 15 MHz frequency range.

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Publication Date
07-Sep-2015
Technical Committee
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PPUB - Publication issued
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08-Sep-2015
Completion Date
08-Sep-2015
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IEC TS 62791:2015 - Ultrasonics - Pulse-echo scanners - Low-echo sphere phantoms and method for performance testing of gray-scale medical ultrasound scanners applicable to a broad range of transducer types
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IEC TS 62791
Edition 1.0 2015-09
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Pulse-echo scanners – Low-echo sphere phantoms and method
for performance testing of gray-scale medical ultrasound scanners applicable to
a broad range of transducer types
IEC TS 62791:2015-09(en)
---------------------- Page: 1 ----------------------
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IEC TS 62791
Edition 1.0 2015-09
TECHNICAL
SPECIFICATION
colour
inside
Ultrasonics – Pulse-echo scanners – Low-echo sphere phantoms and method
for performance testing of gray-scale medical ultrasound scanners applicable to
a broad range of transducer types
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 11.040.50; 17.140.50 ISBN 978-2-8322-2902-6

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 62791:2015 © IEC 2015
CONTENTS

FOREWORD ........................................................................................................................... 6

INTRODUCTION ..................................................................................................................... 8

1 Scope ............................................................................................................................ 10

2 Normative references .................................................................................................... 10

3 Terms and definitions .................................................................................................... 10

4 Symbols ........................................................................................................................ 12

5 General and environmental conditions ........................................................................... 13

6 Equipment required ....................................................................................................... 14

6.1 General ................................................................................................................. 14

6.2 Phantom geometries ............................................................................................. 14

6.2.1 Phantoms for use in the frequency range 2 MHz to 7 MHz ............................. 14

6.2.2 Phantoms for use in the frequency range 7 MHz to 15 MHz including

"micro-convex" arrays .................................................................................... 14

6.2.3 Total internal-reflection surfaces .................................................................... 15

6.2.4 Spatially random distribution of low-echo spheres.......................................... 15

6.3 Ultrasonic properties of the tissue-mimicking (TM) phantoms ................................ 15

7 Data acquisition assuming a spatially random distribution of low-echo spheres ............. 16

7.1 Methodology ......................................................................................................... 16

7.2 Storage of digitized image data ............................................................................. 17

7.3 Digital image files available from the scanner itself ............................................... 18

7.4 Image archiving systems ....................................................................................... 18

8 Automated data analysis for quantifying low-echo sphere detectability .......................... 18

8.1 General ................................................................................................................. 18

8.2 Computation of mean pixel values (MPVs) ............................................................ 18

8.3 Determination of the LSNR -value for a given depth interval ................................. 21

8.3.1 Preliminaries ................................................................................................. 21

8.3.2 Computation of the LSNR -values and LSNR -value in a given depth
n m

interval .......................................................................................................... 21

8.3.3 Standard error corresponding to each LSNR -value........................................ 21

Annex A (informative) Example of a phantom for performance testing in the 2 MHz to

7 MHz frequency range ......................................................................................................... 22

Annex B (informative) Illustrations of the computation of LSNR -values as a function

of depth ................................................................................................................................ 24

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

results .................................................................................................................................. 29

C.1 General ................................................................................................................. 29

C.2 Phantom with low-echo sphere diameter 3,2 mm, having 2 spheres per

millilitre ................................................................................................................. 29

C.3 Phantom with 2 mm-diameter, low-echo spheres and 8 spheres per millilitre ........ 32

Annex D (informative) Example of a phantom for performance testing in the 7 MHz to

15 MHz frequency range ....................................................................................................... 36

Annex E (informative) Determination of low-echo sphere positions to within D/8 in x, y

and z Cartesian coordinates .................................................................................................. 39

E.1 Procedure ............................................................................................................. 39

E.2 Argument for the choice of seven MPV nearest-neighbour sites for

determining the centres of low-echo spheres ........................................................ 40

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IEC TS 62791:2015 © IEC 2015 – 3 –

Annex F (informative) Test of total internal reflection produced by alumina and plate-

glass, plane reflectors ........................................................................................................... 41

Annex G (informative) Results of a test of reproducibility of LSNR versus depth for a

phantom with 4 mm-diameter low-echo spheres and 2 spheres per millilitre .......................... 48

Annex H (informative) Results for low-echo sphere-concentration dependence of

LSNR versus depth for phantoms with 4 mm-diameter spheres ......................................... 50

Annex I (informative) Results for low-echo sphere-concentration dependence of

LSNR versus depth for phantoms with 3,2 mm-diameter spheres ........................................ 53

Annex J (informative) Comparison of two different makes of scanner with similar

transducers and console settings .......................................................................................... 57

Annex K (informative) Special considerations for 3-D probes .............................................. 59

K.1 3-D probes operating in 2-D imaging mode ........................................................... 59

K.2 2-D arrays operating in 3-D imaging mode for determining LSNR -values as

a function of depth for reconstructed images ......................................................... 59

K.3 Mechanically driven 3-D probes operating in 3-D imaging mode ............................ 59

Bibliography .......................................................................................................................... 60

Figure 1 – Flow chart ............................................................................................................ 17

Figure 2 – Schematic of an image plane ............................................................................... 20

Figure A.1 – End view of the phantom applicable for 2 MHz to 7 MHz showing the

spatially random distribution of 4-mm diameter low-echo spheres ......................................... 22

Figure A.2 – Top view of phantom with 4 mm-diameter, low-echo spheres ............................ 23

Figure B.1 – Convex-array image of a prototype 4 mm-diameter low-echo sphere

phantom for use in the 2 MHz to 7 MHz frequency range ...................................................... 24

Figure B.2 – Auxiliary figures relating to Figure B.1 .............................................................. 25

Figure B.3 – Results corresponding to Figures B.1 and B.2, demonstrating

reproducibility ....................................................................................................................... 25

Figure B.4 – Results corresponding to Figures B.1, B.2 and B.3 ........................................... 26

Figure B.5 – One of 80 parallel linear-array images of the phantom containing 4 mm-

diameter, low-echo spheres, at 4 MHz with focus at 3 cm ..................................................... 26

Figure B.6 – Three successive images of the set of 80, separated by D/4 equal to

1 mm .................................................................................................................................... 27

Figure B.7 – Results for the 4 cm-wide, 3 cm-focus, linear array addressed in Figures

B.5 and B.6 ........................................................................................................................... 27

Figure B.8 – Results for the 4 cm-wide, 3 cm-focus, linear array addressed in

Figures B.5, B.6 and B.7, using all 80 image frames corresponding to Figure B.7 ................. 28

Figure C.1 – One image obtained from a phantom containing 3,2 mm-diameter, low-

echo spheres by using a 4 MHz linear array focused at 3 cm ................................................ 29

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 ........................ 30

Figure C.3 – Results obtained by using both sets of 70 independent images

corresponding to Figure C.2 .................................................................................................. 30

Figure C.4 – Sector image (curved array) at 4,5 MHz with multiple foci at 4 cm, 8 cm

and 12 cm depths; the low-echo spheres are 3,2 mm in diameter ......................................... 31

Figure C.5 – Reproducibility results for a multiple-lateral-focus (4 cm, 8 cm and 12 cm)

case corresponding to Figure C.4 ......................................................................................... 31

Figure C.6 – Reproducibility results for the case corresponding to Figure C.5, except

that there is a single focus at 10 cm depth ............................................................................ 32

Figure C.7 – Reproducibility results for the case corresponding to Figure C.5, except

that there is a single focus at 4 cm depth .............................................................................. 32

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– 4 – IEC TS 62791:2015 © IEC 2015
Figure C.8 – Image of the phantom containing 2 mm-diameter, low-echo spheres,

made with a curved array having 1,5 cm radius of curvature, with its focus at 3 cm .............. 33

Figure C.9 – Reproducibility results corresponding to Figure C.8 .......................................... 33

Figure C.10 – Results using all 100 images in the image set that gave rise to

Figure C.9 ............................................................................................................................. 34

Figure C.11 – Image of the phantom containing 2 mm-diameter, low-echo spheres,

made with a high-frequency (15 MHz) linear array, laterally focused at 4 cm......................... 34

Figure C.12 – Reproducibility results corresponding to Figure C.11 ...................................... 35

Figure C.13 – Results using all 200 images in the image set that gave rise to Figure

C.12 ...................................................................................................................................... 35

Figure D.1 – End- and top-view diagrams of the phantom containing 2 mm-diameter,

low-echo spheres for use in the 7 MHz to 15 MHz frequency range....................................... 37

Figure D.2 – Image obtained by using the phantom containing 2 mm-diameter, low-

echo spheres and a pediatric transducer with a radius of curvature of about 1,5 cm ............. 38

Figure F.1 – Average of 10 images obtained by using a phased array ................................... 42

Figure F.2 – Plot of the data with blue data computed in the left rectangle in Figure F.1

and red data computed in the right rectangle ........................................................................ 42

Figure F.3 – Plot of the data when the reflector is on the right side with blue computed

in the left rectangle and red computed in the right rectangle ................................................. 43

Figure F.4 – The percentage by which the mean pixel values resulting from reflections

differ from the mean pixel values not involving reflections ..................................................... 44

Figure F.5 – Wide sector (153°), 1 cm-radius-of-curvature transducer with alumina

reflector on the left ................................................................................................................ 45

Figure F.6 – Plot of the data with blue computed in the left rectangle in Figure F.5 and

red computed in the right rectangle ....................................................................................... 45

Figure F.7 – Plot of the data when the reflector is on the right side with blue computed

in the left rectangle and red computed in the right rectangle ................................................. 46

Figure F.8 – The percentage by which the mean pixel values resulting from reflections

differ from the mean pixel values not involving reflections ..................................................... 46

Figure G.1 – Example image of the phantom with a 4,2 MHz curved array and two low-

echo spheres per millilitre ..................................................................................................... 48

Figure G.2 – Reproducibility results corresponding to the image set, one of which is

shown in Figure G.1 .............................................................................................................. 49

Figure H.1 – Example of an image from the image set giving rise to the results in

Figure H.2; the phantom contained an average of one 4 mm-diameter, low-echo sphere

per millilitre ........................................................................................................................... 50

Figure H.2 – Results corresponding to an image set, one of which is shown in Figure

H.1 51

Figure H.3 – Example of an image from the data set giving rise to the results in Figure

H.4; the phantom contained an average of two 4 mm-diameter, low-echo spheres per

millilitre ................................................................................................................................. 51

Figure H.4 – Results corresponding to an image set, one of which is shown in Figure

H.3 52

Figure I.1 – Example of an image from the 4 ml data set producing the results shown

in Figure I.2 .......................................................................................................................... 53

Figure I.2 – Results for the phantom containing four 3,2 mm-diameter, low-echo

spheres per millilitre.............................................................................................................. 54

Figure I.3 – Example of an image from the 2 ml data set producing the results shown

in Figure I.4 .......................................................................................................................... 54

Figure I.4 – Results for the phantom containing two 3,2 mm-diameter, low-echo

spheres per millilitre.............................................................................................................. 55

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IEC TS 62791:2015 © IEC 2015 – 5 –

Figure I.5 – Example of an image from the 1 ml data set producing the results shown

in Figure I.6 .......................................................................................................................... 55

Figure I.6 – Results for the phantom containing one 3,2 mm-diameter, low-echo sphere

per millilitre ........................................................................................................................... 56

Figure J.1 – Results for System A scanner and 7CF2 3-D (swept convex array)

transducer focused at 4 cm and operated at 4,5 MHz in 2-D mode ........................................ 57

Figure J.2 – Results for System B scanner with a 4DC7-3 3-D (convex array)

transducer, operated at 4 MHz in 2-D mode and focused at 4 cm. The sector angle and

all other console settings mimicked those for the System A case (Figure J.1) ....................... 57

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– 6 – IEC TS 62791:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ULTRASONICS – PULSE-ECHO SCANNERS – LOW-ECHO
SPHERE PHANTOMS AND METHOD FOR PERFORMANCE
TESTING OF GRAY-SCALE MEDICAL ULTRASOUND SCANNERS
APPLICABLE TO A BROAD RANGE OF TRANSDUCER TYPES
FOREWORD

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Technical Specifications are subject to review within three years of publication to decide

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Technical Specification IEC TS 62791 has been prepared by IEC technical committee 87

Ultrasonics.
---------------------- Page: 8 ----------------------
IEC TS 62791:2015 © IEC 2015 – 7 –
The text of this Technical Specification is based on the following documents:
DTS Report on voting
87/554/DTS 87/570/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.

Terms in bold in the text are defined in Clause 3.

The committee has decided that the contents of this publication will remain unchanged until

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A bilingual version of this publication may be issued at a later date.
---------------------- Page: 9 ----------------------
– 8 – IEC TS 62791:2015 © IEC 2015
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. 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/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. 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. All the foregoing transducer types commonly operate within the frequency range

2 MHz to 15 MHz, to which this Technical Specification applies.

A 2-dimensional array (2-D array) is restricted to an array of transducer elements distributed

over a square 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 sections 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 cyst-like (low-echo) object is distinguished from the

surrounding soft tissue, i.e. the degree to which a small cyst-like (low-echo) object 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 delineate the boundary of an abnormal object, such as a tumour. 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 should be given equal weight in measuring detectability. A

sphere has no preferred orientation and is therefore the best shape for a cyst-like object for

two rea
...

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