IEC 61391-1:2006/AMD1:2017
(Amendment)Amendment 1 - Ultrasonics - Pulse-echo scanners - Part 1: Techniques for calibrating spatial measurement systems and measurement of point-spread function response
Amendment 1 - Ultrasonics - Pulse-echo scanners - Part 1: Techniques for calibrating spatial measurement systems and measurement of point-spread function response
Amendement 1 - Ultrasons - Scanners à impulsion et écho - Partie 1: Techniques pour l'étalonnage des systèmes de mesure spatiaux et des mesures de la réponse de la fonction de dispersion ponctuelle du système
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IEC 61391-1 ®
Edition 1.0 2017-07
INTERNATIONAL
STANDARD
colour
inside
AMENDMENT 1
Ultrasonics – Pulse-echo scanners –
Part 1: Techniques for calibrating spatial measurement systems and
measurement of system point-spread function response
IEC 61391-1:2006-07/AMD1:2017-07(en)
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IEC 61391-1 ®
Edition 1.0 2017-07
INTERNATIONAL
STANDARD
colour
inside
AMENDMENT 1
Ultrasonics – Pulse-echo scanners –
Part 1: Techniques for calibrating spatial measurement systems and
measurement of system point-spread function response
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.140.50 ISBN 978-2-8322-4289-6
– 2 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
FOREWORD
This amendment has been prepared by IEC technical committee 87: Ultrasonics.
The text of this amendment is based on the following documents:
FDIS Report on voting
87/650/FDIS 87/653/RVD
Full information on the voting for the approval of this amendment 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 website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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.
____________
2 Normative references
Replace:
IEC 61102:1991, Measurement and characterisation of ultrasonic fields using hydrophones in
the frequency range 0,5 MHz to 15 MHz
with:
IEC 62127-1:2007, Ultrasonics – Hydrophones – Part 1: Measurement and characterization of
medical ultrasonic fields up to 40 MHz
Insert the following new normative references in proper numerical sequence:
IEC 60050-801:1994, International Electrotechnical Vocabulary – Chapter 801: Acoustics and
electroacoustics
© IEC 2017
IEC 60050-802:2011, International Electrotechnical Vocabulary – Part 802: Ultrasonics
3 Terms and definitions
Replace the first two paragraphs with the following new paragraph:
For the purposes of this document, the terms and definitions given in IEC 60050-801:1994,
IEC 60050-802:2011, IEC 62127-1:2007 and the following apply. See also related
International Standards, Technical Specifications and Technical Reports for definitions and
explanations [1] [2] [3] [4] [34] [35] [36] [37] [38] [39].
3.25
point-spread function
PSF
Add the following new sentence at the end of the NOTE:
The problem is solved by PSF mapping – see Annex D.
Add the following new terms and definitions to Clause 3, starting with 3.45.
3.45
accuracy
closeness of agreement between a test result and the accepted reference value
[SOURCE: ISO 5725-1:1994, 3.6]
3.46
axial resolution in a PSF-map
twice the Half-Width-at-Half-Maximum (HWHM) of a function’s trace created from a set of
increasing pixel values, commencing near zero and terminating at the first maximum value
(centre of the PSF) and representing the leading edge of the echo signal from a point reflector
located on the main beam axis
Note 1 to entry: The axial resolution in a PSF map differs from the axial resolution specified by 3.5. It is used
for the PSF-mapping only to simplify the data acquisition.
Note 2 to entry: A detailed explanation of the axial resolution in the PSF-map measuring method is in D.6.1.4.
Note 3 to entry: The axial resolution mainly depends on the ultrasound frequency used, not on sonograph
construction.
Note 4 to entry: Axial resolution in a PSF-map is expressed in metres.
3.47
brightness
luminance as perceived by the human visual system
[SOURCE: IEC 62563-1:2009, 3.1.2]
3.48
contrast
C
ratio of the difference of the luminance of two image areas, L − L , divided by the average of
1 2
the two luminance values:
C = 2 (L − L )/(L + L )
1 2 1 2
[SOURCE: IEC 62563-1:2009, 3.1.6]
– 4 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
3.49
dynamic imaging
real-time imaging
imaging with a frame rate that is high enough to observe moving structures in apparently
continuous motion
3.50
elevational resolution in a PSF-map
difference of point-reflector displacements in passing through the scanning plane in an
elevational direction, which result in decreases of MER of −6 dB compared to the MER-value
in the beam centre
Note 1 to entry: The elevational resolution in a PSF-map differs from the elevational resolution specified by
3.12. It is used for the PSF-mapping only to simplify the data acquisition.
Note 2 to entry: Detailed explanation of the method is in D.6.1.3.
Note 3 to entry: Elevational resolution in a PSF-map is expressed in metres.
3.51
overall gain
G
o
basic level of gain that is uniform for the whole scan area but modified by TGC relative to the
depth of the scan
3.52
profile line
set of pixel values ordered along an abscissa according to the sequence during their
acquisition
3.53
lateral resolution in a PSF-map
Full-Width at Half-Maximum (FWHM) of the PSF, measured in a lateral direction
Note 1 to entry: The lateral resolution in a PSF-map differs from the lateral resolution specified by 3.17. It is
used for the PSF-mapping only to simplify the data acquisition.
Note 2 to entry: Detailed explanation of the method is in D.6.1.2.
Note 3 to entry: Lateral resolution in a PSF-map is expressed in metres.
3.54
measuring grid
matrix of points specified by Cartesian coordinates x and z defined in a plane parallel to the
i j
scanning plane
Note 1 to entry: Each point determines the position (x ,z ) in which individual measurement of PSF is performed.
i j
Note 2 to entry: The step ∆x is defined as an increment x – x in the lateral direction. The step ∆z is defined as
i+1 i
an increment z – z in the axial direction.
j+1 j
3.55
performance evaluation
tests performed to assess specific absolute performance of the object tested
Note 1 to entry: Typical times for ultrasound-system performance evaluation are at pre-purchase evaluation,
new- and repaired-system acceptance testing, at time of performance difficulties, and at end-of-useful-life
evaluations.
[SOURCE: IEC TS 62736:2016, 3.5]
© IEC 2017
3.56
precision
closeness of agreement between independent test results obtained under stipulated
conditions
[SOURCE: ISO 5725-1:1994, 3.12]
3.57
scanning window
area on the surface of the test tank dedicated for transducer application to obtain a suitable
sonogram of the target
Note 1 to entry: It is important that the scanning window be covered by flexible foil made of material with similar
acoustic properties to the working liquid to avoid ultrasound field reflections and absorption.
Note 2 to entry: The foil flexibility should assure proper acoustical contact of any type of curved transducer.
Note 3 to entry: It is important that the foil covering the scanning-window be tough enough to prevent its damage
during coupling the measured transducer to the scanning window, to prevent resultant leakage of working liquid
from the measuring tank.
Note 4 to entry: The scanning window has the identical function as the test object scanning surface in the
case of tissue-mimicking test objects (see 3.34).
3.58
side-lobe signal
echo signal generated by ultrasound signal transmitted/received in a direction different from
the central axis of the transducer
3.59
test tank
tank designed to be suitable for providing specified kind of tests, which is filled with a
working liquid and equipped with scanning window(s)
Replace the title of Clause 4 with the following new title:
4 Symbols and abbreviated terms
Add the following symbols and abbreviated terms to Clause 4:
D diameter of the reflector sphere
A greatest a evaluated for whole measured volume
r,max r,max
a MER pixel value evaluated from ROI
r,max
a (x,y,z) MER pixel value evaluated from ROI scanned for reflector in position (x,y,z)
r,max
C contrast
G overall gain
o
I(x,y,z) ROI specified in a digital picture of scan stored with reflector in position (x,y,z)
m
M number of quantization levels defined by M = 2 where m is number of pixel
bits
p pixel size in lateral (azimuthal) direction
x
p pixel size in axial direction
z
R axial resolution in a PSF-map
A,PSF
R elevational resolution in a PSF-map
E,PSF
R lateral resolution in a PSF-map
L,PSF
W value of FWHM (full width at half of maximum)
F,HM
– 6 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
W value of HWHM (half width at half of maximum)
H,HM
W normalized W according to Formula (D.3) in D.6.1.2
F,HM,n F,HM
W normalized W according to Formula (D.3) in D.6.1.2
H,HM,n H,HM
λ ultrasound wavelength in the working liquid, calculated from the nominal
frequency of the transducer used
ATGC automatic time-gain compensation
FWHM full width at half of maximum
HFHM half width at half of maximum
LUT look-up table
MER maximum echo received
PSF point-spread function
RF radio frequency
ROI region of interest
TGC time-gain compensation
US ultrasound
6.1 Test methods
Replace:
c) a tank containing degassed working liquid.
with:
c) a tank equipped with target holder to position the target at accurately specified
positions and containing degassed working liquid.
Replace:
The specifications of these devices are given in the annexes.
with:
The specifications of these devices are given in Annexes A, B, C and D.
8.2 Test methods
Replace:
b) a tank containing degassed liquid;
with:
b) a tank containing degassed liquid and, optionally, movable targets as described in
Clause C.4 and D.5.4.2;
8.4.1 General
Add, at the end of 8.4.1, the following new sentence:
“A setting should be specified by a test instruction for each test, if it differs from the general
recommendations. See D.5.2.”
© IEC 2017
8.5.1 General
Add, to the end of the fifth paragraph starting “To overcome this limitation …”, the following
new text:
“The complications generated by interference and multiple reflections inside the spherical
target may be solved by time-domain analysis of the received echo when a larger and/or
highly reflective sphere is used. See D.5.4.2.”
8.5.4 Scan slice thickness (elevational PSF and LSF) or elevational resolution
Add, at the end of 8.5.4, the following new text:
“The most accurate and flexible method to derive the complex set of parameters based on the
PSF mapping analysis is described in Annex D.”
C.4 Movable single filament or wire in water (Figures C.3, C.4)
Add, at the end of Clause C.4, the following new single-sentence paragraph:
“The use of a movable spherical target for assessing quality parameters derived by PSF-
mapping analysis is described in Annex D. ”
Insert after Annex C the following new Annex D
– 8 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
Annex D
(informative)
Quality parameters derived by PSF-mapping analysis
D.1 General
A quality assessment system is vitally needed to provide an accurate and well-defined set of
production-quality parameters for new or refurbished scanners or transducers in acceptance
tests before their introduction to medical practice. It is important that products delivered by
third-party sales groups, system-refurbishers and/or transducer manufacturers be carefully
tested to be able to declare technical parameters of their products to be comparable to those
of the new, originally manufactured systems. The methods used for quality assessment in
medical applications are not certain and accurate enough to be used for such kinds of
technical performance evaluation. PSF-mapping analysis gives reliable parameters suitable
for this kind of tests. These parameters do not directly indicate the effectivity of a clinical
diagnostic process, even though a close correlation between the assessed technical quality
and success in the diagnostic process may be expected [40].
The ultrasound scanner used as a diagnostic system is composed of the system-control/user-
interface unit and the ultrasonic-transducer assembly. Either unit can contain the transmitter-
and the receiver- electronic systems and some of the beam-former electronics. The
ultrasonic transducer converts electrical signals to ultrasound field and vice versa. Electrical
and acoustic parameters of the transducer determine quality of the scanning ultrasound
beam. The electronic system controls the transmitted and received ultrasound signal,
conversion from mechanical to electrical signals, and the signal processing and conversion to
video-signal inputted to the imaging unit. The imaging unit transfers the information to the
human preceptors. The PSF-distribution analysis evaluates qualitative parameters of the
whole ultrasound-scanner system, excluding the display unit. The analysed signal is affected
by the quality of the whole imaging cycle, and the transmitting and receiving parts of the
scanner. The analysed system function is affected by a complex set of control functions.
Therefore, it is important that the combination of the control settings of the scanner be exactly
specified and recorded as a part of the measurement.
D.2 Method
Annex D describes a method for precise and reliable measurement of several qualitative
parameters of whole ultrasound scanning systems including both the transmitting and
receiving parts of the systems, excluding the parameters of scanner display. The method is
based on PSF-distribution analysis over a scanning area. In the case of PSF-mapping, the
measured parameters are derived by analysis of sonograms generated by scanning a
spherical target moving over a defined scanning volume on a specified trajectory.
The PSF-mapping system evaluates a set of parameters acquired over a user-defined area in
one scanning plane of a B-mode grey-scale sonogram, scanned in a tank filled by degassed
working liquid and using one measuring procedure. The whole target sonogram is not
evaluated in the PSF-mapping analysis. The test signal is obtained by reflection of a
transmitted ultrasound wave from a point-reflector surface and working-liquid boundary only.
The point reflector used is a highly reflective sphere of diameter D [41].
The method is suitable for all kinds of echo(reflections)-evaluating sonographs using different
types of beam-forming and plane-wave compounding of ultrasound signal in the frequency
range 0,5 MHz to 50 MHz. The upper frequency limit is determined by a ball target of
minimum diameter available to assure reflection effectivity and fulfil the condition λ ≤ D ≤ 4λ,
where λ is the ultrasound wavelength in the working liquid [42]. Further limiting factors are a
minimum size of step and precise mechanical construction of the positioning system to assure
measurement reliability and adequate scan size.
© IEC 2017
The method is relevant for all the types of transducers used with these scanners, including
• mechanical probes including annular arrays,
• electronic phased arrays,
• linear arrays,
• curved arrays,
• two-dimensional arrays, and
• 3D-volume scanning probes based on a combination of the above types.
The PSF-measuring system is not a tissue-mimicking object. It is dedicated to performing
accurate, stable and reliable measurements under conditions appropriate to achieving these
measurements of parameters, some of which may be obtained by use of sophisticated
electronic measurements of the scanner’s electronic system and some by PSF-mapping
analysis only [43].
The following data are acquired and are analysed using the method:
a) the ROI digital image stored for the scanned-plane axis in each point of the measuring
grid;
b) the echo-signal amplitude distribution over the measured area;
c) the distribution of the parameter W which is Full-Width-at-Half-Maximum (FWHM) of
F,HM
the point-spread function (PSF) in the azimuthal direction over the measured area;
d) the distribution of the parameter W Half-Width-at-Half-Maximum (HWHM) of the point-
H,HM
spread function (PSF) in the axial direction over the measured area;
e) the peak echo-amplitude received a (x,y,z) at each y step of the target position in the
r,max k
elevation (transversal) direction;
f) the (x,y,z) coordinates set for stored position of the point reflector generating a (x,y,z)
r,max
from MER in each point of the measuring grid (position in centre of ultrasound beam).
Data analysis derives the following ultrasound scanner parameters and functions:
1) focal areas in both the azimuth and the elevation directions;
2) visualization of the distribution of ultrasound scanning lines;
3) manufacturer’s preloaded TGC function;
4) width (elevation) of the scanning plane over the depth of scan;
5) side-lobes signal-level distribution in the scan plane;
6) amplification uniformity in the azimuth direction;
7) scan geometry linearity and accuracy.
D.3 Environmental conditions
The most temperature-sensitive parameters are those assessing geometry of the sonogram
and related calculations. The temperature-dependent deviations may be compensated
mathematically from known working-liquid temperature and thermal coefficient of speed of
sound.
Water condensation on electronic system components should be avoided.
D.4 General requirements of the method
Ultrasound waves produce a PSF-signal that is neither singular nor isotropic. Furthermore,
the ultrasound PSF can be asymmetrical, having different axial and lateral dimensions, and it
– 10 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
also varies with distance from the transducer in both the axial and the azimuthal directions.
Thus, it is important that many different measurements of the PSF at different positions and
depths be performed to obtain representative values of the system’s imaging performance at
specific positions along the beam axis. It is also important that the measured area be covered
by a grid of the measuring points, the density of which is determined by the expected
parameters and the accuracy of the measurement [44].
NOTE For example, determination of a focal point’s position may need an axial step ∆z = 5 mm; visualization of
scanning lines demands an azimuthal step ∆x = 0,1 mm for a conventional linear transducer of nominal frequency
3 MHz.
The following features are necessary to apply the PSF-analyser to the sonograph:
a) The sonograph to be tested:
– video-signal output of live, dynamic scanning available in analog (composite) or digital
(DVI-D, HDMI) form;
– operating instructions or skilled operator to assure proper manipulation and operating
adjustment;
– record of proper evidence and registration of the measurement process, including
identification of operator and all apparatus used, record of parameters preset in the
measured system, record of environmental conditions, including a time stamp.
b) The basic configuration of the measurement tank:
– The scanning window(s) is(are) localized in the side wall(s) of the tank.
– The spherical-target positioning system is fixed on top of the tank, controlling
movement of the target fixed in a holder.
– Filling the tank with degassed working liquid is recommended to prevent bubble
generation in the working fluid. Bubbles may mimic the point reflector and/or produce
spurious reflections from the point reflector after having accumulated on it, due to
surface tension.
– Temperature should be kept in the specified range to eliminate measurement
uncertainties generated by dependence of the speed of ultrasound propagation upon
temperature.
c) The transducer:
– The transducer is acoustically coupled to the scanning window by standard coupling
ultrasound gel. The scanning window is covered by tough, flexible foil made of
material with similar acoustic properties to the working liquid to avoid ultrasound field
reflections and absorption.
– The scanning plane is oriented in the horizontal direction and the transducer is fixed to
keep the whole slice thickness below the water surface. It is important that the lateral
orientation of the transducer be specified.
d) The positioning system:
– A computer-controlled micromanipulator is used to move the target or transducer to a
determined position. It is important that mechanical construction, accuracy and
stability of the positioning system correspond with ultrasound frequency. The shorter
the wavelength, the more accurate and robust the system should be to avoid
systematic measuring errors.
e) The control and analysing system:
– The software controls the video-signal acquisition, determines ROI, selects and saves
the ROI frames to be used for analysis and finally maintains the complex analysis of
the stored information.
– The basic parameters used for PSF-analysis are the W (Full Width at Half
F,HM
Maximum, i.e. at −6 dB down from a ) and the pixel level of noise at an area
r,max
without reflections.
© IEC 2017
– The W depends upon the intensity of the received signal. Therefore, it is important
F,HM
that the receiving gain and output power be properly adjusted to utilize the whole
dynamic range of the analyser.
D.5 Measuring conditions
D.5.1 General
In Figure D.1 a principal schematic of the PSF-analyser is introduced. The PSF-analyser
consists of the data-acquisition components (test-tank and point-reflector parts of the
schema), a linear transducer, a personal computer (PC) with video-signal input, running
acquisition and analysis software. The sonograph being measured is shown with a linear
transducer but the results analysis is displayed for a sector-scan transducer to illustrate
transducer-type independency of the system.
Tested system
Sono-
graph
Video
PC
ROI
PSF
IEC
Figure D.1 – Principal schematic of the PSF-analyser function
D.5.2 Sonograph
D.5.2.1 General
Sonographs are equipped with a large set of different control functions to ensure optimal
handling of received ultrasound signals to create the best image. These control functions
affect remarkably the measurement results because the method evaluates the signal after it
has passed through a whole imaging system. Therefore, it is important that all the
adjustments and settings be carefully documented in the measuring protocol to be available
for use for repeated measurements.
Test tank
Transducer
Grabber
– 12 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
D.5.2.2 The amplitude transfer-characteristic adjustment
The sonograph receiver employs a logarithmic amplifier to compress a very wide range of
received signal amplitudes (more than 100 dB). It is important that all the other additional,
nonlinear, so-called pre-processing and post-processing functions be switched off or adjusted
to linear working regions to avoid further nonlinear distortions of the signal. This requirement
includes functions dedicated to eliminating different types of noise either by scan-sequences
correlation or averaging or cutting off low-level signals.
It is important that the amplified signal-peak amplitude limitation due to low amplifier dynamic
range be eliminated to assure correct measurement of the FWHM-function. Therefore, it is
also important that the widest dynamic range accessible by the measuring system be selected,
except in the case when the gain of the sonograph is not sufficient to achi
...
IEC 61391-1 ®
Edition 1.0 2017-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
A MENDMENT 1
AM ENDEMENT 1
Ultrasonics – Pulse-echo scanners –
Part 1: Techniques for calibrating spatial measurement systems and
measurement of system point-spread function response
Ultrasons – Scanners à impulsion et écho –
Partie 1: Techniques pour l'étalonnage des systèmes de mesure spatiaux et des
mesures de la réponse de la fonction de dispersion ponctuelle du système
IEC 61391-1:2006-07/AMD1:2017-07 (en-fr)
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IEC 61391-1 ®
Edition 1.0 2017-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
A MENDMENT 1
AM ENDEMENT 1
Ultrasonics – Pulse-echo scanners –
Part 1: Techniques for calibrating spatial measurement systems and
measurement of system point-spread function response
Ultrasons – Scanners à impulsion et écho –
Partie 1: Techniques pour l'étalonnage des systèmes de mesure spatiaux et des
mesures de la réponse de la fonction de dispersion ponctuelle du système
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-5557-5
– 2 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
FOREWORD
This amendment has been prepared by IEC technical committee 87: Ultrasonics.
This bilingual version (2018-04) corresponds to the monolingual English version, published in
2017-07.
The text of this amendment is based on the following documents:
FDIS Report on voting
87/650/FDIS 87/653/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The French version of this amendment has not been voted upon.
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 website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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.
____________
2 Normative references
Replace:
IEC 61102:1991, Measurement and characterisation of ultrasonic fields using hydrophones in
the frequency range 0,5 MHz to 15 MHz
with:
IEC 62127-1:2007, Ultrasonics – Hydrophones – Part 1: Measurement and characterization of
medical ultrasonic fields up to 40 MHz
Insert the following new normative references in proper numerical sequence:
© IEC 2017
IEC 60050-801:1994, International Electrotechnical Vocabulary – Chapter 801: Acoustics and
electroacoustics
IEC 60050-802:2011, International Electrotechnical Vocabulary – Part 802: Ultrasonics
3 Terms and definitions
Replace the first two paragraphs with the following new paragraph:
For the purposes of this document, the terms and definitions given in IEC 60050-801:1994,
IEC 60050-802:2011, IEC 62127-1:2007 and the following apply. See also related
International Standards, Technical Specifications and Technical Reports for definitions and
explanations [1] [2] [3] [4] [34] [35] [36] [37] [38] [39].
3.25
point-spread function
PSF
Add the following new sentence at the end of the NOTE:
The problem is solved by PSF mapping – see Annex D.
Add the following new terms and definitions to Clause 3, starting with 3.45.
3.45
accuracy
closeness of agreement between a test result and the accepted reference value
[SOURCE: ISO 5725-1:1994, 3.6]
3.46
axial resolution in a PSF-map
twice the Half-Width-at-Half-Maximum (HWHM) of a function’s trace created from a set of
increasing pixel values, commencing near zero and terminating at the first maximum value
(centre of the PSF) and representing the leading edge of the echo signal from a point reflector
located on the main beam axis
Note 1 to entry: The axial resolution in a PSF map differs from the axial resolution specified by 3.5. It is used
for the PSF-mapping only to simplify the data acquisition.
Note 2 to entry: A detailed explanation of the axial resolution in the PSF-map measuring method is in D.6.1.4.
Note 3 to entry: The axial resolution mainly depends on the ultrasound frequency used, not on sonograph
construction.
Note 4 to entry: Axial resolution in a PSF-map is expressed in metres.
3.47
brightness
luminance as perceived by the human visual system
[SOURCE: IEC 62563-1:2009, 3.1.2]
3.48
contrast
C
ratio of the difference of the luminance of two image areas, L − L , divided by the average of
1 2
the two luminance values:
– 4 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
C = 2 (L − L )/(L + L )
1 2 1 2
[SOURCE: IEC 62563-1:2009, 3.1.6]
3.49
dynamic imaging
real-time imaging
imaging with a frame rate that is high enough to observe moving structures in apparently
continuous motion
3.50
elevational resolution in a PSF-map
difference of point-reflector displacements in passing through the scanning plane in an
elevational direction, which result in decreases of MER of −6 dB compared to the MER-value
in the beam centre
Note 1 to entry: The elevational resolution in a PSF-map differs from the elevational resolution specified by
3.12. It is used for the PSF-mapping only to simplify the data acquisition.
Note 2 to entry: Detailed explanation of the method is in D.6.1.3.
Note 3 to entry: Elevational resolution in a PSF-map is expressed in metres.
3.51
overall gain
G
o
basic level of gain that is uniform for the whole scan area but modified by TGC relative to the
depth of the scan
3.52
profile line
set of pixel values ordered along an abscissa according to the sequence during their
acquisition
3.53
lateral resolution in a PSF-map
Full-Width at Half-Maximum (FWHM) of the PSF, measured in a lateral direction
Note 1 to entry: The lateral resolution in a PSF-map differs from the lateral resolution specified by 3.17. It is
used for the PSF-mapping only to simplify the data acquisition.
Note 2 to entry: Detailed explanation of the method is in D.6.1.2.
Note 3 to entry: Lateral resolution in a PSF-map is expressed in metres.
3.54
measuring grid
matrix of points specified by Cartesian coordinates x and z defined in a plane parallel to the
i j
scanning plane
Note 1 to entry: Each point determines the position (x ,z ) in which individual measurement of PSF is performed.
i j
Note 2 to entry: The step ∆x is defined as an increment x – x in the lateral direction. The step ∆z is defined as
i+1 i
an increment z – z in the axial direction.
j+1 j
3.55
performance evaluation
tests performed to assess specific absolute performance of the object tested
Note 1 to entry: Typical times for ultrasound-system performance evaluation are at pre-purchase evaluation,
new- and repaired-system acceptance testing, at time of performance difficulties, and at end-of-useful-life
evaluations.
© IEC 2017
[SOURCE: IEC TS 62736:2016, 3.5]
3.56
precision
closeness of agreement between independent test results obtained under stipulated
conditions
[SOURCE: ISO 5725-1:1994, 3.12]
3.57
scanning window
area on the surface of the test tank dedicated for transducer application to obtain a suitable
sonogram of the target
Note 1 to entry: It is important that the scanning window be covered by flexible foil made of material with similar
acoustic properties to the working liquid to avoid ultrasound field reflections and absorption.
Note 2 to entry: The foil flexibility should assure proper acoustical contact of any type of curved transducer.
Note 3 to entry: It is important that the foil covering the scanning-window be tough enough to prevent its damage
during coupling the measured transducer to the scanning window, to prevent resultant leakage of working liquid
from the measuring tank.
Note 4 to entry: The scanning window has the identical function as the test object scanning surface in the
case of tissue-mimicking test objects (see 3.34).
3.58
side-lobe signal
echo signal generated by ultrasound signal transmitted/received in a direction different from
the central axis of the transducer
3.59
test tank
tank designed to be suitable for providing specified kind of tests, which is filled with a
working liquid and equipped with scanning window(s)
Replace the title of Clause 4 with the following new title:
4 Symbols and abbreviated terms
Add the following symbols and abbreviated terms to Clause 4:
D diameter of the reflector sphere
A greatest a evaluated for whole measured volume
r,max r,max
a MER pixel value evaluated from ROI
r,max
a (x,y,z) MER pixel value evaluated from ROI scanned for reflector in position (x,y,z)
r,max
C contrast
overall gain
G
o
I(x,y,z) ROI specified in a digital picture of scan stored with reflector in position (x,y,z)
m
M number of quantization levels defined by M = 2 where m is number of pixel
bits
p pixel size in lateral (azimuthal) direction
x
p pixel size in axial direction
z
R axial resolution in a PSF-map
A,PSF
R elevational resolution in a PSF-map
E,PSF
R lateral resolution in a PSF-map
L,PSF
– 6 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
W value of FWHM (full width at half of maximum)
F,HM
W value of HWHM (half width at half of maximum)
H,HM
W normalized W according to Formula (D.3) in D.6.1.2
F,HM,n F,HM
W normalized W according to Formula (D.3) in D.6.1.2
H,HM,n H,HM
λ ultrasound wavelength in the working liquid, calculated from the nominal
frequency of the transducer used
ATGC automatic time-gain compensation
FWHM full width at half of maximum
HFHM half width at half of maximum
LUT look-up table
MER maximum echo received
PSF point-spread function
RF radio frequency
ROI region of interest
TGC time-gain compensation
US ultrasound
6.1 Test methods
Replace:
c) a tank containing degassed working liquid.
with:
c) a tank equipped with target holder to position the target at accurately specified
positions and containing degassed working liquid.
Replace:
The specifications of these devices are given in the annexes.
with:
The specifications of these devices are given in Annexes A, B, C and D.
8.2 Test methods
Replace:
b) a tank containing degassed liquid;
with:
b) a tank containing degassed liquid and, optionally, movable targets as described in
Clause C.4 and D.5.4.2;
8.4.1 General
Add, at the end of 8.4.1, the following new sentence:
“A setting should be specified by a test instruction for each test, if it differs from the general
recommendations. See D.5.2.”
© IEC 2017
8.5.1 General
Add, to the end of the fifth paragraph starting “To overcome this limitation …”, the following
new text:
“The complications generated by interference and multiple reflections inside the spherical
target may be solved by time-domain analysis of the received echo when a larger and/or
highly reflective sphere is used. See D.5.4.2.”
8.5.4 Scan slice thickness (elevational PSF and LSF) or elevational resolution
Add, at the end of 8.5.4, the following new text:
“The most accurate and flexible method to derive the complex set of parameters based on the
PSF mapping analysis is described in Annex D.”
C.4 Movable single filament or wire in water (Figures C.3, C.4)
Add, at the end of Clause C.4, the following new single-sentence paragraph:
“The use of a movable spherical target for assessing quality parameters derived by PSF-
mapping analysis is described in Annex D. ”
Insert after Annex C the following new Annex D
– 8 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
Annex D
(informative)
Quality parameters derived by PSF-mapping analysis
D.1 General
A quality assessment system is vitally needed to provide an accurate and well-defined set of
production-quality parameters for new or refurbished scanners or transducers in acceptance
tests before their introduction to medical practice. It is important that products delivered by
third-party sales groups, system-refurbishers and/or transducer manufacturers be carefully
tested to be able to declare technical parameters of their products to be comparable to those
of the new, originally manufactured systems. The methods used for quality assessment in
medical applications are not certain and accurate enough to be used for such kinds of
technical performance evaluation. PSF-mapping analysis gives reliable parameters suitable
for this kind of tests. These parameters do not directly indicate the effectivity of a clinical
diagnostic process, even though a close correlation between the assessed technical quality
and success in the diagnostic process may be expected [40].
The ultrasound scanner used as a diagnostic system is composed of the system-control/user-
interface unit and the ultrasonic-transducer assembly. Either unit can contain the transmitter-
and the receiver- electronic systems and some of the beam-former electronics. The
ultrasonic transducer converts electrical signals to ultrasound field and vice versa. Electrical
and acoustic parameters of the transducer determine quality of the scanning ultrasound
beam. The electronic system controls the transmitted and received ultrasound signal,
conversion from mechanical to electrical signals, and the signal processing and conversion to
video-signal inputted to the imaging unit. The imaging unit transfers the information to the
human preceptors. The PSF-distribution analysis evaluates qualitative parameters of the
whole ultrasound-scanner system, excluding the display unit. The analysed signal is affected
by the quality of the whole imaging cycle, and the transmitting and receiving parts of the
scanner. The analysed system function is affected by a complex set of control functions.
Therefore, it is important that the combination of the control settings of the scanner be exactly
specified and recorded as a part of the measurement.
D.2 Method
Annex D describes a method for precise and reliable measurement of several qualitative
parameters of whole ultrasound scanning systems including both the transmitting and
receiving parts of the systems, excluding the parameters of scanner display. The method is
based on PSF-distribution analysis over a scanning area. In the case of PSF-mapping, the
measured parameters are derived by analysis of sonograms generated by scanning a
spherical target moving over a defined scanning volume on a specified trajectory.
The PSF-mapping system evaluates a set of parameters acquired over a user-defined area in
one scanning plane of a B-mode grey-scale sonogram, scanned in a tank filled by degassed
working liquid and using one measuring procedure. The whole target sonogram is not
evaluated in the PSF-mapping analysis. The test signal is obtained by reflection of a
transmitted ultrasound wave from a point-reflector surface and working-liquid boundary only.
The point reflector used is a highly reflective sphere of diameter D [41].
The method is suitable for all kinds of echo(reflections)-evaluating sonographs using different
types of beam-forming and plane-wave compounding of ultrasound signal in the frequency
range 0,5 MHz to 50 MHz. The upper frequency limit is determined by a ball target of
minimum diameter available to assure reflection effectivity and fulfil the condition λ ≤ D ≤ 4λ,
where λ is the ultrasound wavelength in the working liquid [42]. Further limiting factors are a
minimum size of step and precise mechanical construction of the positioning system to assure
measurement reliability and adequate scan size.
© IEC 2017
The method is relevant for all the types of transducers used with these scanners, including
• mechanical probes including annular arrays,
• electronic phased arrays,
• linear arrays,
• curved arrays,
• two-dimensional arrays, and
• 3D-volume scanning probes based on a combination of the above types.
The PSF-measuring system is not a tissue-mimicking object. It is dedicated to performing
accurate, stable and reliable measurements under conditions appropriate to achieving these
measurements of parameters, some of which may be obtained by use of sophisticated
electronic measurements of the scanner’s electronic system and some by PSF-mapping
analysis only [43].
The following data are acquired and are analysed using the method:
a) the ROI digital image stored for the scanned-plane axis in each point of the measuring
grid;
b) the echo-signal amplitude distribution over the measured area;
c) the distribution of the parameter W which is Full-Width-at-Half-Maximum (FWHM) of
F,HM
the point-spread function (PSF) in the azimuthal direction over the measured area;
d) the distribution of the parameter W Half-Width-at-Half-Maximum (HWHM) of the
H,HM
point-spread function (PSF) in the axial direction over the measured area;
e) the peak echo-amplitude received a (x,y,z) at each y step of the target position in the
r,max k
elevation (transversal) direction;
f) the (x,y,z) coordinates set for stored position of the point reflector generating a (x,y,z)
r,max
from MER in each point of the measuring grid (position in centre of ultrasound beam).
Data analysis derives the following ultrasound scanner parameters and functions:
1) focal areas in both the azimuth and the elevation directions;
2) visualization of the distribution of ultrasound scanning lines;
3) manufacturer’s preloaded TGC function;
4) width (elevation) of the scanning plane over the depth of scan;
5) side-lobes signal-level distribution in the scan plane;
6) amplification uniformity in the azimuth direction;
7) scan geometry linearity and accuracy.
D.3 Environmental conditions
The most temperature-sensitive parameters are those assessing geometry of the sonogram
and related calculations. The temperature-dependent deviations may be compensated
mathematically from known working-liquid temperature and thermal coefficient of speed of
sound.
Water condensation on electronic system components should be avoided.
D.4 General requirements of the method
Ultrasound waves produce a PSF-signal that is neither singular nor isotropic. Furthermore,
the ultrasound PSF can be asymmetrical, having different axial and lateral dimensions, and it
– 10 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
also varies with distance from the transducer in both the axial and the azimuthal directions.
Thus, it is important that many different measurements of the PSF at different positions and
depths be performed to obtain representative values of the system’s imaging performance at
specific positions along the beam axis. It is also important that the measured area be covered
by a grid of the measuring points, the density of which is determined by the expected
parameters and the accuracy of the measurement [44].
NOTE For example, determination of a focal point’s position may need an axial step ∆z = 5 mm; visualization of
scanning lines demands an azimuthal step ∆x = 0,1 mm for a conventional linear transducer of nominal frequency
3 MHz.
The following features are necessary to apply the PSF-analyser to the sonograph:
a) The sonograph to be tested:
– video-signal output of live, dynamic scanning available in analog (composite) or digital
(DVI-D, HDMI) form;
– operating instructions or skilled operator to assure proper manipulation and operating
adjustment;
– record of proper evidence and registration of the measurement process, including
identification of operator and all apparatus used, record of parameters preset in the
measured system, record of environmental conditions, including a time stamp.
b) The basic configuration of the measurement tank:
– The scanning window(s) is(are) localized in the side wall(s) of the tank.
– The spherical-target positioning system is fixed on top of the tank, controlling
movement of the target fixed in a holder.
– Filling the tank with degassed working liquid is recommended to prevent bubble
generation in the working fluid. Bubbles may mimic the point reflector and/or produce
spurious reflections from the point reflector after having accumulated on it, due to
surface tension.
– Temperature should be kept in the specified range to eliminate measurement
uncertainties generated by dependence of the speed of ultrasound propagation upon
temperature.
c) The transducer:
– The transducer is acoustically coupled to the scanning window by standard coupling
ultrasound gel. The scanning window is covered by tough, flexible foil made of
material with similar acoustic properties to the working liquid to avoid ultrasound field
reflections and absorption.
– The scanning plane is oriented in the horizontal direction and the transducer is fixed to
keep the whole slice thickness below the water surface. It is important that the lateral
orientation of the transducer be specified.
d) The positioning system:
– A computer-controlled micromanipulator is used to move the target or transducer to a
determined position. It is important that mechanical construction, accuracy and
stability of the positioning system correspond with ultrasound frequency. The shorter
the wavelength, the more accurate and robust the system should be to avoid
systematic measuring errors.
e) The control and analysing system:
– The software controls the video-signal acquisition, determines ROI, selects and saves
the ROI frames to be used for analysis and finally maintains the complex analysis of
the stored information.
– The basic parameters used for PSF-analysis are the W (Full Width at Half
F,HM
Maximum, i.e. at −6 dB down from a ) and the pixel level of noise at an area
r,max
without reflections.
© IEC 2017
– The W depends upon the intensity of the received signal. Therefore, it is important
F,HM
that the receiving gain and output power be properly adjusted to utilize the whole
dynamic range of the analyser.
D.5 Measuring conditions
D.5.1 General
In Figure D.1 a principal schematic of the PSF-analyser is introduced. The PSF-analyser
consists of the data-acquisition components (test-tank and point-reflector parts of the
schema), a linear transducer, a personal computer (PC) with video-signal input, running
acquisition and analysis software. The sonograph being measured is shown with a linear
transducer but the results analysis is displayed for a sector-scan transducer to illustrate
transducer-type independency of the system.
Tested system
Sono-
graph
Video
PC
ROI
PSF
IEC
Figure D.1 – Principal schematic of the PSF-analyser function
D.5.2 Sonograph
D.5.2.1 General
Sonographs are equipped with a large set of different control functions to ensure optimal
handling of received ultrasound signals to create the best image. These control functions
affect remarkably the measurement results because the method evaluates the signal after it
has passed through a whole imaging system. Therefore, it is important that all the
adjustments and settings be carefully documented in the measuring protocol to be available
for use for repeated measurements.
Test tank
Transducer
Grabber
– 12 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
D.5.2.2 The amplitude transfer-characteristic adjustment
The sonograph receiver employs a logarithmic amplifier to compress a very wide range of
received signal amplitudes (more than 100 dB). It is important that all the other additional,
nonlinear, so-called pre-processing and post-processing functions be switched off or adjusted
to linear working regions to avoid further nonlinear distortions of the signal. This requirement
includes functions dedicated to eliminating different types of noise either by scan-sequences
correlation or averaging or cutting off low-level signals.
It is important that the amplified signal-peak amplitude limitation due to low amplifier dynamic
range be eliminated to assure correct measurement of the FWHM-function. Therefore, it is
also important that the widest dynamic range accessible by the measuring system be selected,
except in the case when the gain of the sonograph is not sufficient to achieve full dynamic
range for the A .
r,max
D.5.2.3 The look-up table setting
The relation of the grey-scale level to the digitalized amplitude of the signal is derived from a
look-up table (LUT) or Gamma curve. If possible to assure a pure logarithmic characteristic of
the system, only a most linear LUT should be used. It is important that all the settings be
documented in the measuring protocol, to be recorded for use during further periodical
measurements. A method to find the most linear LUT should be part of the measuring
software.
D.5.2.4 The measured gain adjustment
The sonograph’s receiver gain is controlled in two parts: the overall gain (G ) and the
o
time-gain compensation (TGC) functions. Their adjustment prior to measurement should be
as follows: The TGC is adjusted first. The basic condition is to adjust the TGC to be constant
within the whole range of the scanned depth. The basic condition of the TGC adjustment is its
independence from the depth parameter (elimination of the function). Then the G is
o
increased to just obtain little visible thermal noise of the system in an echo-free area on the
screen, e.g. when the transducer is energized when coupled to the air. It is important that the
G be decreased or a smaller reflector used, if the A amplitude limitation occurs.
o r,max
Some sonographs utilize an ATGC (automatic time gain compensation) function. It is
important that this function be disabled for gain (sensitivity) dependence from depth and
focal-points localization from MER-profile assessments.
D.5.3 Measuring tank
D.5.3.1 General
The measuring tank serves as a holder of the volume of homogenous non-reflecting medium –
the working liquid – in which the point reflector is moving by the precise, computer-controlled
electromechanical system. An appropriate scanning window allows effective acoustic
connection between the working liquid inside the tank and the active part of the measured
transducer. The size of the measuring tank should be appropriate to the size of largest
scanned area expected.
D.5.3.2 Working liquid
It is important that the working liquid used in the tank be degassed to avoid collection of
bubbles at the point reflector [45]. It is also important that the temperature be recorded for the
measurements to be based on accurate values of speed of sound, which significantly affects
reading geometry of the scan. However, measurements based on reading the echo intensity
are not remarkably affected by working liquid temperature because temperature dependence
of both the reflectivity and the water absorption are negligible in this case.
© IEC 2017
The accuracy of the distance calculations is determined by the accuracy of knowledge of
ultrasound speed of propagation in the working liquid. The coefficient of speed of ultrasound
-1 -1
in pure water as a function of temperature is approximately 4 ms °C in the temperature
range 10 °C to 30 °C. According to the distance calculation from the echo delay, a change of
temperature of ±1 °C results in error of ±0,15 % of the measured distance value. A calculation
giving the temperature error compensation is possible by use of an expression given by [46]
or another by [47].
D.5.3.3 Reflections
Due to low ultrasound absorption of the working liquid and high reflectivity of the tank walls
and relatively small size of the measuring tank, many multiple reflections are generated in the
scanned area. These multiple reflections may be eliminated by a simple system of absorbers
and reflector shielding because a pulsed signal is generated and only a small ROI
surrounding and close to the reflector is analysed in the sonogram.
D.5.3.4 Scanning windows
The ultrasound signal is transferred between transducer and reflector via the scanning
window. The window works as an acoustic coupler between the active surface of the
transducer and the working liquid. The window is closed with flexible foil made of material with
similar acoustic properties to the working liquid to assure effective transfer of the ultrasound
signal and elimination of ultrasound-signal reflections and absorption. The transducer is
attached to the foil with use of conventional coupling gel so that the whole active surface of
the transducer is in acoustic contact with the working liquid. Proper shape of the window is
needed to assure effective contact of different types of transducers. The measured transducer
holder is part of the scanning window. Its design should ensure adjustment of the scanning
plane to be parallel to the xz-plane of the target positioning system and stable transducer
positions during measurement.
D.5.4 Target
D.5.4.1 General
The target system is composed of the sphere reflector, the reflector holder and the reflector
positioning system.
D.5.4.2 Reflector
In contrast to C.4 and Figure C.4, the point reflector is not the flat end of a wire but a sphere
made of steel or similar highly reflective material. The reflector is fixed to a positioning system
with use of a holder made of tiny, hard wire. The sphere reflection is independent of the
incident angle of irradiation.
The diameter D of the rigid metallic reflector is critical for the method used but should be kept
within a range λ < D < 4λ according to [42]. Use of a reflector of D < λ is possible, but the
reflected signal amplitude will not be strong enough for low-sensitivity systems. Therefore
decrease of the target diameter, D, may be employed when too-sensitive sonographs limit
high amplitude of signals, even if the overall gain G and output power are adjusted to
o
minimum levels (see D.5.2.4).
If D > 4λ, values and variations of the W increase to an erroneous extent in both the
F,HM
lateral and the elevational directions.
The reflections from any inner structure of the sphere and multiple reflections in the sphere
and/or sphere resonances [48] [49] are eliminated in the received-signal evaluation process.
They do not affect the measurement results. The PSF-mapping method evaluates reflections
of a transmitted ultrasound wave from a point-reflector surface and working-liquid boundary
only (Figure D.2). It is important that the sphere reflector be made of a highly reflective
– 14 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
material, i.e. the difference of characteristic acoustic impedance of the working liquid and
sphere-target material should be as high as possible.
LF UP Olomouc biofyzika
GEN-[PSF SIMUACE]
Transducer
ROI
Depth (Number of pixels)
Depth (Time)
Separated in the ROI
IEC
IEC
In the top figure, RF signal amplitude is converted to pixel
The yellow rectangle specifies ROI. The green line brightness, time domain to space domain. The ROI
corresponds with the signal displayed in b). separated for analysis is marked.
A linear transducer, nominal frequency 10 MHz, In the bottom figure, the RF signal corresponds with the
was used. green line in a).
a) Scan of spherical target 0,6 mm diameter b) Process of demodulation (top) and the target-scan
received-RF signal (bottom)
NOTE The late reflections are not included in the analysed data.
Figure D.2 – Principle of elimination of internal multi-reflections
in the spherical target using filtration in time domain
D.5.4.3 Sphere holder
The holder fixes the sphere to the positioning system. It is important that the holder
construction avoid any influence upon the reflected signal. It is also important that the
connection be rigid enough to eliminate any shift of the target during its displacement in the
water, due to hydraulic resistance. A possible alternative for such a holder is a tiny, stiff wire
bent to rectangular form of the letter L with the sphere fixed on one end (the bottom –
horizontally oriented) of the wire while the second (the top) end is mounted to the positioning
system. It is important that the wire diameter be smaller than D, but the ratio is not critical.
Reflections from the holder are positioned outside the ROI; therefore they do not affect the
measurement results.
The holder construction should allow easy replacement (exchange) of the sphere reflector to
allow use of sphere reflectors of various diameters, according to the transducer’s nominal
frequency and the fundamental wavelength of ultrasound in the working liquid (λ < D < 4λ).
D.5.4.4 Positioning system
The positioning system (micro-manipulator) is dedicated to placing the sphere within the
scanned area in the working liquid. The required system accuracy and stiffness is determined
by the measuring ultrasound frequency and transducer-scanning parameters.
D.5.5 Signal acquisition
It is important that live, full-resolution video be captured from the sonograph for processing
the measurements.
Separated in the ROI
RF signal amplitude
Pixel amplitude
© IEC 2017
Two basic types of signals are available from the sonograph output. The old and low-end
types are equipped with analog composite VHS video output in PAL standard only. The newer
and higher technological level systems do not use the obsolete analog video but use digital
video DVI-D or HDMI outputs. Both types of video signal need special hardware
(video-grabber) to be acquired by the computer for further analysis. Most higher end systems
have direct digitally detected- and/or IQ-data output.
The following parameters of the acquired video signal are essential for recording and analysis:
• the ultrasound scanner frame rate;
• dynamic range and amplitude resolution (quantization-step size);
• spatial resolution of the sonograph, related to number of lines for analog video signals
and/or size of pixel for digital video signals.
The digital resolution parameters are not too critical for the resolution of the measurement
results, because the analysing system may interpolate between adjacent, discrete values.
The pixel value corresponds to echo amplitude received. The amplitude dynamic range of the
analysed input signal is derived from the video monitor’s grey-level range, which is 256 grey
levels at maximum. Therefore, 8-bit (256 grey levels) digitalization is a minimum to fulfil the
needs of inputted analog-signal conversion.
D.5.6 Signal analysis
The system grabs a continuously recorded video signal from the sonograph. Prior to running
the acquisition, a proper region of interest (ROI) is chosen in the sonogram. The software
controls ROI position according to the target placement in the scanning plane to keep the
target inside the ROI. Only those ROI frames are used for further analysis, which coincide
with the target position in the pre-programmed measuring grid at points (x,z) within the
measured volume of the scan. Each of these ROIs is analysed to find the pixel containing
a (x,z) the highest value of MER when the target moves in an elevation (y) direction. Not
r,max
whole ROIs but only their highest pixel value a (x,y,z) is stored for each y, including the
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corresponding target position (x,y,z) for each elevation path. Only one ROI containing the
highest of the a (x,y,z) from each elevation set (x,z) is stored as a picture I(x,y,z). The
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stored I(x,y,z) is a picture of the target on the central (axis) of the ultrasound beam and
therefore may be analysed to find the PSF in both the azimuth and the axial directions. See
Figure D.3 and Figure D.4.
The input video-signal level and the transfer characteristic of the video-grabber may affect the
measurement results when the input data are obtained from a composite video signal. Thus, it
is important that the video-grabber amplitude-transfer characteristic be well adjusted to
assure use of the whole range of the AD-converter to prevent artificial limitation of the high
level signal.
The digital video-grabber transfer function does not affect the measurement results when
digital video-signal input is used.
An example of the PSF derived from the data recorded in one point of the measuring-grid is
presented in Figure D.3.
– 16 – IEC 61391-1:2006/AMD1:2017
© IEC 2017
IEC
NOTE The white line is the line of PSF-acquisition from the digital picture of the target at position (x,y,z). The line
passes through the pixel containing the maximum of the signal a (x,y,z).
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Figure D.3 – A pixel maximum level and PSF-trace estimation in ROI stored digital data
D.6 Results – measured parameters
D.6.1 Spatial resolutions in PSF-mapping
D.6.1.1 General
The PSF-mapping method demands modification of the spatial-resolution evaluation method
defined earlier (See 3.46, 3.50 and 3.53). The assessment of target displacement complicates
the mapping process; it has been changed to simply deriving the spatial resolution value in
PSF-mapping from a single measurement in the measuring-grid point. The values of mapped
parameters may differ slightly from the ones defined earlier (3.46, 3.50 and 3.53), but they are
measured with higher accuracy and repeatability when using the mapping system [44].
The spatial resolution is defined as a distance. The lateral and axial resolutions are
enumerated from FWHM- and/or HWHM-parameters, respectively. These parameters are
derived from the PSF in number of pixels and recalculation using the pixel size in a scanned
area is needed. The elevational resolution is derived directly from positions of the reflector
generating half-maximum reflected signal during vertical displacement of the reflector.
The lateral- and axial-resolution conversion to units of distance should be performed by
evaluatin
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