Applications of Advanced Ultrasound Technology in Obstetrics
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diagnostics
Review
Applications of Advanced Ultrasound Technology in Obstetrics
Kwok-Yin Leung
Obstetrics and Gynaecology, Gleneagles Hong Kong, Hong Kong, China; ky@kyleung.org
Abstract: Over the years, there have been several improvements in ultrasound technologies including
high-resolution ultrasonography, linear transducer, radiant flow, three-/four-dimensional (3D/4D)
ultrasound, speckle tracking of the fetal heart, and artificial intelligence. The aims of this review are
to evaluate the use of these advanced technologies in obstetrics in the midst of new guidelines on and
new techniques of obstetric ultrasonography. In particular, whether these technologies can improve
the diagnostic capability, functional analysis, workflow, and ergonomics of obstetric ultrasound
examinations will be discussed.
Keywords: obstetrics; ultrasound; 3D; 4D; Doppler; artificial intelligence
1. Introduction
Ultrasound is widely used in obstetric practice to detect fetal abnormalities with a
view to provide prenatal opportunities for further investigations including genetic testing
and discussion of management options. In 2010, International Societies of Ultrasound in
Obstetrics and Gynecology (ISUOG) published the practice guidelines on the minimal
and optional requirements for a routine mid-trimester ultrasound scan [1]. Recently, The
Citation: Leung, K.-Y. Applications American Institute of Ultrasound in Medicine (AIUM) suggests a detailed diagnostic
of Advanced Ultrasound Technology second/third trimester scan for high-risk pregnancies [2], and fetal echocardiography for
in Obstetrics. Diagnostics 2021, 11, at-risk pregnancies [3]. ISUOG has published recent guidelines on indications and practice
1217. https://doi.org/10.3390/ of targeted neurosonography [4,5]. Although the introduction of prenatal cell-free DNA-
diagnostics11071217 based screening for Down syndrome has changed the role of the first trimester scan, the
latter should still be offered to women [6]. Around 50% of major structural abnormalities
Academic Editor: Ritsuko can be detected in the first trimester [7]. In addition, a recent study showed that a routine
Kimata Pooh
scan at around 36 weeks’ gestation can detect around 0.5% of previously undetected fetal
abnormalities, as well as fetal growth restriction (FGR) [8].
Received: 7 June 2021
The detection rate of fetal abnormalities varies, depending on anatomy survey pro-
Accepted: 3 July 2021
tocol, ultrasound equipment and setting, among other factors [9]. A high-resolution
Published: 6 July 2021
ultrasound can facilitate a detailed diagnostic scan and a first-trimester scan and allow the
detection of a small or subtle abnormality [10–12]. Although a detailed diagnostic scan is
Publisher’s Note: MDPI stays neutral
not required for all pregnant women, the indications include family history of congenital
with regard to jurisdictional claims in
malformation, maternal age 35 or above, gestational diabetes mellitus, artificial reproduc-
published maps and institutional affil-
iations.
tion technology, body mass index >= 30, teratogen, fetal nuchal translucency >= 3mm, and
many other conditions [2]. In the midst of such increasing standards of obstetric ultrasound
examination, there is a demand on improving the diagnostic capability, functional anal-
ysis, workflow, and ergonomics. Over the years, there have been several improvements
in ultrasound technologies including high-resolution ultrasonography, linear transducer,
Copyright: © 2021 by the author.
radiant flow, three/four-dimensional (3D/4D) ultrasound, speckle tracking of the fetal
Licensee MDPI, Basel, Switzerland.
heart, and artificial intelligence. The aim of this review is to evaluate the use of these
This article is an open access article
advanced technologies in obstetrics.
distributed under the terms and
conditions of the Creative Commons
2. High-Resolution Ultrasonography
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/ High-resolution ultrasonography includes the use of a high-frequency transducer,
4.0/). and the means of enhancing image and signal processing including harmonic imaging
Diagnostics 2021, 11, 1217. https://doi.org/10.3390/diagnostics11071217 https://www.mdpi.com/journal/diagnostics
2. High-Resolution Ultrasonography
High-resolution ultrasonography includes the use of a high-frequency tra
Diagnostics 2021, 11, 1217 and the means of enhancing image and signal processing including 2 ofharmonic
18
(HI), spatial compound imaging (SCI), and speckle reduction imaging (SRI). Com
a transducer with the low-frequency range (2 to 5 MHz), a transducer with the
(HI), spatial compound
quency range imaging (SCI), can
(5 to 9 MHz) and allow
speckle reduction
for improved imaging (SRI). though
resolution Compared with limit
to a transducer with the low-frequency range (2 to 5 MHz), a transducer with the high-
penetration. HI, utilizing the physics of non-linear propagation of ultrasound thr
frequency range (5 to 9 MHz) can allow for improved resolution though with limited tissue
body tissues, can produce high-resolution images with few artifacts. SCI, combin
penetration. HI, utilizing the physics of non-linear propagation of ultrasound through
the body tiple lines
tissues, canof sight to
produce form a singleimages
high-resolution composite image
with few at real-time
artifacts. frame rates, ca
SCI, combining
angle-dependent
multiple lines of sight to formartifacts. The use of
a single composite SRIatcan
image reduceframe
real-time speckles
rates, or
candisturbances
reduce th
from theartifacts.
angle-dependent echo, which
The useis projected from an
of SRI can reduce ultrasound
speckles transducer.
or disturbances that result
from the echo, which is projected from an ultrasound transducer.
2.1. Fetal Echocardiography and Targeted Neurosonography
2.1. Fetal Echocardiography and Targeted Neurosonography
ISUOG recommends the use of the highest possible transducer frequency to
ISUOG recommends the use of the highest possible transducer frequency to perform
fetal echocardiography with a view to improve the likelihood of detecting sub
fetal echocardiography with a view to improve the likelihood of detecting subtle heart de-
defects,
fects, albeit albeit atofthe
at the expense expense
reduced of reduced
acoustic acoustic
penetration penetration
[10] (Figure 1a–d and[10] (Figure
Video S1). 1a–d an
The use ofS1).
HI The use of HI
can improve thecan improve
quality the quality
of ultrasound of ultrasound
images, images,
especially when especially when
the maternal
abdominal ternal
wall abdominal wall
is thick during theisthird
thick duringof
trimester the third trimester
pregnancy [11,13]. of pregnancy [11,13].
(a) (b)
(c) (d)
Figure 1. High-resolution
Figure 1.ultrasonography of the fetal heartofatthe
High-resolution ultrasonography 20 fetal
weeks’ gestation
heart showing
at 20 weeks’ (a) a four-chamber
gestation showing (a) a view sh
ing right atrium (RA), left atrium
four-chamber view(LA), right
showing ventricle
right (RV),left
atrium (RA), and left (LA),
atrium ventricle
right (LV), (b)(RV),
ventricle five-chamber view showing
and left ventricle
cending aorta (AAo) arising
(LV), from the left
(b) five-chamber viewventricle, the right aorta
showing ascending and left superior
(AAo) arising pulmonary
from the left veins (RSPV,
ventricle, LSPV) ente
the right
left atrium (LA), and
anddescending
left superioraorta (DAo)veins
pulmonary behind the LSPV)
(RSPV, LA (c)enter
Three-vessel view(LA),
the left atrium showing the PA dividing
and descending aorta into the
(LPA) and right (RPA)
(DAo)PA, AAo,
behind theand
LA the superior vena
(c) Three-vessel viewcava (SVC),
showing the(d)
PAthree-vessel
dividing intoandthe trachea
left (LPA) view
and showing
right PA
the ductal branch (DA)
(RPA)joining
PA, AAo, theand
DAo,
the AAo, SVC,
superior venaand trachea
cava (SVC),(T);
(d) Thymus is anterior
three-vessel to the
and trachea viewthree vessels.
showing PA
with the ductal branch (DA) joining the DAo, AAo, SVC, and trachea (T); Thymus is anterior to the
three vessels. For a targeted neurosonographic examination, ISUOG recommends the use
resolution transvaginal transducers whenever possible [5]. An alternative is to u
Diagnostics 2021, 11, 1217 3 of 18
Diagnostics 2021, 11, x FOR PEER REVIEW 3 of 18
For a targeted neurosonographic examination, ISUOG recommends the use of high-
resolution transvaginal transducers whenever possible [5]. An alternative is to use high-
resolution transabdominal
resolution transabdominal transducers
transducers with
with high
high frequency
frequency reaching
reaching 8–9
8–9 MHz
MHz [5].
[5]. The
The
anatomy of
anatomy of the
thefetal
fetalbrain
brainisisexamined
examinedin in
details on on
details a continuum of transverse,
a continuum sagittal
of transverse, and
sagittal
coronal
and planes
coronal (Figure
planes 2a–d,2a–d,
(Figure Video S2a,b).
Video S2a,b).
(a) (b)
(c) (d)
Figure 2. High-resolution ultrasonography
ultrasonography of of the fetal brain at 20 weeks’ gestation: transverse views showing (a) posterior
horn of
horn of the
the lateral
lateral ventricle
ventricle (Vp),
(Vp), (b)
(b) cavum
cavum septi
septi pellucidi
pellucidi (C.S.P.),
(C.S.P.), (c)
(c) cerebellum
cerebellum (Cereb),
(Cereb), Cisterna
Cisterna magna
magna (CM),
(CM), nuchal
nuchal
fold (NF), and sagittal view showing (d) corpus callosum (CC), thalamus (TH), brain stem (BS), and cerebellar
fold (NF), and sagittal view showing (d) corpus callosum (CC), thalamus (TH), brain stem (BS), and cerebellar vermis (CV). vermis
(CV).
2.2. Face and Neck
2.2. Face and Neck
While the prenatal detection of cleft lip is high, the detection rate of subtle abnor-
While
malities the prenatal
of face detection
such as low-set orof cleft lip is rotating
posteriorly high, theear,detection rateface,
triangular of subtle abnormal-
down-slanting
ities of face such as low-set or posteriorly rotating ear, triangular face,
palpebral fissures, or a long and marked philtrum remains low [14,15]. These subtle abnor- down-slanting pal-
pebral fissures, or a long and marked philtrum remains low [14,15].
malities may be features of rare but severe genetic disorders such as 5p deletion syndromeThese subtle abnor-
malities may be which
or RASopathy, features of rarechromosome
require but severe genetic disorders
microarray such as
analysis or5p deletionsequencing
targeted syndrome
or
forRASopathy,
RASopathywhich genes.require
As such,chromosome microarray
it is important to performanalysis or targeted
a detailed sequencing
ultrasound scanfor
to
RASopathy
evaluate fetal genes.
face As such, it especially
in fetuses is important to perform
if they have largea detailed ultrasound
NT, heart defects,scan to eval-
or unusual
uate fetal[14,15].
findings face in fetuses especiallyultrasonography
High-resolution if they have largeallows
NT, heartthe defects, or unusual findings
clear visualization of facial
[14,15].
profile, lens, nostrils, lips, maxilla, and ears (Figure 3a–d, Video S3a,b). of
High-resolution ultrasonography allows the clear visualization facial profile,
Recently, a new
lens, nostrils,sign,
sonographic lips, the
maxilla, and ears (Figure
‘superimposed line’ sign,3a–d, Video S3a,b).
is suggested Recently, aof new
for evaluation so-
the sec-
nographic
ondary palatesign,bythe ‘superimposed
assessment of theline’ sign, is suggested
vomeromaxillary for evaluation
junction of the secondary
in the midsagittal view of
palate by assessment
the palate [16] (Figureof3a).
the vomeromaxillary junction in the midsagittal view of the palate
[16] (Figure 3a).
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18
(a) (a) (b) (b)
(c) (c) (d) (d)
Figure 3. High-resolution
Figure 3. High-resolution ultrasonographyultrasonography
Figure 3. High-resolution
of the fetal of the
face at 20fetal
ultrasonography face at 20
of the
weeks’ weeks’
fetal (a)atgestation:
face
gestation: 20 weeks’(a)gestation:
mid-sagittal mid-sagittal
view view showing facial
(a) mid-sagittal
showing facial
profile, (b) coronal view showing both lens (Le), (c) coronal view showing the upper lip (UL) and two nostrils (No), and the(No), and
profile, (b) coronal
view view
showingshowing
facial both lens
profile, (b)(Le), (c)
coronal coronal
view view
showing showing
both the
lens upper
(Le), (c) lip (UL)
coronal and
view two nostrils
showing
(d) showing
(d) sagittal view sagittal view showing
upper
the ear. theand
lip (UL) ear.two nostrils (No), and (d) sagittal view showing the ear.
Larynx
Larynx and Larynx and itscan
itsmovement
and its movement movement
canbebe canby
assessed
assessed be prenatal
assessed
by by prenatal
prenatal ultrasound
ultrasound ultrasound
4 and(Figure
(Figure
(Figure and 4 and V
4Video
Video S4). InS4). In
at-risk at-risk
fetuses fetuses
such such
as as
those those
with with laryngeal
laryngeal atresia
atresia [17] [17]
and
S4). In at-risk fetuses such as those with laryngeal atresia [17] and congenital diaphrag- and congenital
congenital di- diaph
matic hernia, prenatal ultrasound allows systematic examination of the larynx, including inclu
aphragmatic matic
hernia,hernia, prenatal
prenatal ultrasound
ultrasound allows
allows systematic
systematic examination
examination of of
thethe larynx,
larynx,
including
vocal cords vocal
vocal
to cords
cords
detect to detect
to detect
laryngeal laryngeal
laryngeal
anomalies anomalies
anomalies
[17,18]. [17,18].
[17,18].
Figure 4. High-resolution
Figure4.4. High-resolution
High-resolution ultrasonographyultrasonography
of the
the fetal of the
fetalneck
neck fetal neck at 21 weeks’ gestation:
view sagittal
Figure showing ultrasonography
larynx (Lar) and of
trachea (T). atat21
21 weeks’
weeks’ gestation:
gestation: sagittal
sagittal view
showing larynx (Lar) and trachea (T).
showing larynx (Lar) and trachea (T).
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2.3. Early Pregnancy Scan
2.3. Early PregnancyisScan
Transvaginal ultrasonography essential in the assessment of pregnancy of unknown
location, which can beTransvaginal
due to earlyultrasonography is essential or
pregnancy, miscarriage, in the assessment
ectopic of pregnancy
pregnancy. It is of un
known location, which can be due to early pregnancy, miscarriage,
important to avoid making a false-positive diagnosis of miscarriage by using transvaginal or ectopic pregnancy
sonography, carefulIt measurement
is important toof avoid
mean making a false-positive
sac diameter diagnosis
and crown rumpoflength,
miscarriage by using trans
and using
vaginal sonography, careful measurement of mean sac diameter and crown rump length
safe cut-off values of these measurements in defining miscarriage [19]. A recent study
and using safe cut-off values of these measurements in defining miscarriage [19]. A recen
showed that amniotic sac sign (the presence of amniotic sac without a live embryo) is a
study showed that amniotic sac sign (the presence of amniotic sac without a live embryo
reliable marker of ismiscarriage [20]. While the presence of an extrauterine gestational sac
a reliable marker of miscarriage [20]. While the presence of an extrauterine gestationa
with yolk sac and/or embryo with or without
sac with yolk sac and/or embryocardiac activity
with or is indicative
without of ectopic
cardiac activity preg- of ectopi
is indicative
nancy, the presencepregnancy,
of an inhomogeneous adnexal mass (‘blob’ sign) or extrauterine sac-like
the presence of an inhomogeneous adnexal mass (‘blob’ sign) or extrauterin
sac-like
structure (‘bagel’ sign) structure
is very (‘bagel’ofsign)
suggestive is very
a tubal suggestive
ectopic pregnancyof a [21].
tubal In
ectopic
women pregnancy
with [21]. I
womenultrasound
prior Caesarean section, with prior Caesarean
features ofsection, ultrasound
Caesarean features of Caesarean
scar pregnancy includingscarlowpregnanc
implantation of theincluding
gestationallow sac
implantation
within orofinthe gestational
close proximitysac within or in closescar
to a Caesarean proximity
as wellto a Caesar
as classical signs ofean scar as well
placenta as classical
accreta spectrum signs of placenta
disorders accreta
should bespectrum disorders
looked out should be looke
for [22,23].
out for [22,23].
2.4. First Trimester Scan
2.4. First Trimester Scan
ISUOG and recently, AIUM published the practice guidelines on first-trimester fetal
ultrasound scan [24,25].ISUOG and recently,ultrasonography
High-resolution AIUM published the practice
allows theguidelines on first-trimester
early assessment of feta
ultrasound scan [24,25]. High-resolution ultrasonography allows the early assessment o
fetal anatomy [11] (Figure 5a–d, Video S5a,b) and fetal malformations [12]. Fetal heart
fetal anatomy [11] (Figure 5a–d, Video S5a,b) and fetal malformations [12]. Fetal heart ca
can be examined in the late first trimester [26], particularly with the use of color Doppler
be examined in the late first trimester [26], particularly with the use of color Dopple
(Video S5c,d). ISUOG recommends using high-frequency (6–12 MHz) transvaginal ul-
(Video S5c,d). ISUOG recommends using high-frequency (6–12 MHz) transvaginal ultra
trasound to examine fetal brain, especially
sound to examine fetal brain,ifespecially
the focusif is
theinfocus
the posterior fossa and
is in the posterior the
fossa and the ma
maternal abdominal wall is thick [5].
ternal abdominal wall is thick [5].
(a) (b)
(c) (d)
Figure 5. High-resolution ultrasonography of the fetus at 13 weeks’ gestation: (a) mid-sagittal view
showing head, neck, and facial profile, (b) coronal view showing both eyes and ears, (c) the hand
with five fingers, and (d) foot.
Diagnostics 2021, 11, 1217 6 of 18
2.5. Doppler Ultrasound
Doppler ultrasound is widely used in obstetrics. ISUOG has made recommendations
on how to perform Doppler ultrasonography of the fetoplacental circulation [27]. It is
a challenge to detect late-onset feral growth restriction (FGR). Although third-trimester–
cerebroplacental ratio (CPR = middle cerebral artery pulsatile index/umbilical artery
pulsatile index) is an independent predictor of stillbirth and perinatal mortality [28], CPR
with or without adjustment for estimated fetal weight centile showed a low prediction rate
for adverse perinatal outcome [29]. According to a meta-analysis, abnormal uterine artery
(UtA) Doppler in the third trimester is useful in predicting perinatal death in suspected
small-for-gestational age fetuses [30]. A recent prospective study suggested that cerebral–
placental–uterine ratio (CPUR = CPR divided by mean UtA pulsatile index) detected FGR
better than CPR or UtA Doppler alone [31].
2.6. Labour Ward Ultrasound
The use of intrapartum ultrasonography is increasing. It can be performed by using a
portable machine equipped with a wide-sector and low-frequency (
Diagnostics 2021, 11, x FOR PEER REVIEW 7
Diagnostics 2021, 11, 1217 7 of 18
(a) (b)
(c) (d)
Figure 6. Ultrasonography of a fetus atof
Figure 6. Ultrasonography 13a weeks’
fetus atgestation
13 weeks’ bygestation
a transabdominal high-frequency
by a transabdominal linear transducer: (a
high-frequency
transverse view oftransducer:
linear fetal brain, (b) coronal view
(a) transverse of face
view showing
of fetal brain, both orbits (OB),
(b) coronal view (c) coronal
of face view of
showing abdomen
both orbits showing
both kidneys(OB),
(Ki) (c)
on coronal view of abdomen showing both kidneys (Ki) on either side of the spine, and (d)showing
either side of the spine, and (d) the three-vessel trachea transverse view with color Doppler the pulmo
nary artery (PA), aorta (Ao), superior vena cava (SVC), and trachea (T).
three-vessel trachea transverse view with color Doppler showing pulmonary artery (PA), aorta (Ao),
superior vena cava (SVC), and trachea (T).
4. Radiant Flow
4. Radiant Flow Radiant flow shows the blood flow with a sense of depth by using a specific
rithm
Radiant flow to convert
shows theflow
the blood index of aerythrocyte
with sense of depth density in a acertain
by using specificarea into a height
algorithm
to convert thewhich
indexisofthen superimposed
erythrocyte densityonin thea initial
certaincoding of color,
area into power
a height Doppler,
index whichor high-d
tion flowon
is then superimposed [42].
theOther advantages
initial coding ofinclude reducing
color, power blood overflow
Doppler, and indicating th
or high-definition
flow [42]. Other
sel advantages include
with sharp edges. reducing
Special displayblood overflow
produced by and indicating
similar the vessel
technologies include Micro
with sharp edges. Special
Imaging display
(Philips), produced
MV-Flow, andbyLumiFlow
similar technologies
(Samsung).include MicroFlow
Imaging (Philips), MV-Flow,
Radiant flow andisLumiFlow (Samsung).
used to show fast blood flow in the fetal heart and brachycep
Radiant flow is used to show fast blood
arteries [42] (Videos S5d and S6a,b), as flow in well
the fetal heart and flow
as slow-blood brachycephalic
in the neurovascula
arteries [42] (Videos
culationS5d [43]and S6a,b),
(Video S7). as well as slow-blood flow in the neurovascular
circulation [43] (Video
The S7).
fetal umbilical–portal venous system is complex. High-definition flow im
The fetal (HDFI)
umbilical–portal venous
has been used to system
assess theis complex. High-definition
normal anatomy flow imaging
of this system or umbilical–p
(HDFI) has been used to assess the normal anatomy of this system or umbilical–portal–
systemic venous shunts. Transverse and sagittal planes are used to examine the feta
systemic venous shunts. Transverse
bilical–portal venous systemand (Video
sagittalS8a,b).
planesInare used case
a recent to examine the authors
report, the fetal used
umbilical–portal venous system (Video S8a,b). In a recent case report, the authors
and radiant flow imaging to clearly delineate the aberrant course of the ductus ve used
HDFI and radiant flowto
returning imaging to clearly
the coronary sinusdelineate
[44]. the aberrant course of the ductus
venosus returning to the coronary sinus [44].
5. 3D/4D Ultrasound
5. 3D/4D Ultrasound
Over the years, new 2D modes (such as high-density power imaging), new 3D
Over the years, new 2D modes (such as high-density power imaging), new 3D volume
ume acquisition (such as Corpus callosum mode or matrix probe), and new analysis
acquisition (such as Corpus callosum mode or matrix probe), and new analysis (such as
as semiautomated analysis) have been added in 3D/4D ultrasound examinations (
semiautomated analysis) have been added in 3D/4D ultrasound examinations (Table 1).
1). The use of 3D multiplanar/multislice analysis facilitates the assessment of norma
Diagnostics 2021, 11, 1217 8 of 18
The use of 3D multiplanar/multislice analysis facilitates the assessment of normal and
abnormal structures in standard planes. This can also facilitate the detection of subtle fetal
defects [45]. The use of 3D rendered images can help counseling to the women when fetal
malformations are found or reassure the at-risk women when normal fetal anatomy is
found [45]. 3D/4D US is useful for the assessment of fetal brain, spine, face, heart, and
other structures [45,46].
Table 1. Commonly used scanning mode, volume acquisition, and analysis for three-/four-
dimensional (3D/4D) ultrasound examinations.
Mode Volume Acquisition 3D/4D Analysis
Gray scale 3D: different modes Multiplanar
Color flow 4D Multislice
Power doppler STIC 1 Rendered view: different modes
High-density power imaging Matrix probe Cine loop
B-flow Semi-automatic analysis
Volume measurement
Power Doppler measurements
1 Spatiotemporal image correlation.
Examples in the assessment of fetal abnormalities
a. Cleft lip and palate: use gray-scale mode, after a 3D volume acquisition, perform
multiplanar/multi-slice analysis and rendering techniques to assess the integrity
of palate.
b. Short-limbed and short-rib dysplasia: use gray-scale mode, after a 3D volume ac-
quisition with skeletal mode, perform rendering techniques with skeletal mode to
examine the long bones and ribs.
c. Agenesis of ductus venosus: use high-density power imaging, after a 3D volume
acquisition, perform multi-slice analysis to assess the precordial venous system.
d. Cardiac outflow tract abnormalities: use color flow, after a STIC volume acquisition,
perform multiplanar/multi-slice analysis in a cine-loop of cardiac cycle.
e. Atrioventricular valve abnormalities: use matrix probe and gray-scale mode, real-
time 4D cine-loop analysis to display the coronal view of atrioventricular valve.
5.1. 3D Neurosonography
In targeted neurosonography, a systematic assessment of the fetal brain is required.
Although this assessment can be performed by a 2D ultrasound examination, a perfect
midsagittal view may not be achieved at all times, thus affecting a proper assessment.
ISUOG recommends using 3D ultrasound examination that can provide images of enhanced
resolution by displaying thicker ‘slices’ of the brain and thus increasing the signal-to-
background noise ratio on all three planes. In addition, multiplanar imaging correlation
allows the display of perfectly aligned views on the three orthogonal planes [5]. To avoid
shallowing by adjacent skull bones, it is important to acquire a 3D volume in a mid-
sagittal plane through the sagittal suture. If the focus is on the anterior complex, the
volume will be obtained from the anterior fontanelle or the anterior part of the sagittal
suture [5] (Figure 7a). If the focus is on the posterior fossa and cerebellar vermis, the volume
will be obtained from the posterior fontanelle or the posterior part of the sagittal suture
with the ultrasound beam being almost perpendicular to the tentorium [47] (Figure 7b). A
transvaginal and transabdominal approach is used when the fetal presentation is vertex and
breech, respectively. Then, the midlines structures including corpus callosum, brain stem,
and cerebellar vermis can be examined by multiplanar and multi-slice analysis [43,48,49].
An accurate measurement of corpus callosum and cerebellar vermis can be achieved.
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(a)(a) (b) (b)
Figure
Figure
Figure 7. Three-dimensional
7. Three-dimensional
7. Three-dimensional ultrasonography
ultrasonography
ultrasonographyof
of fetal
fetal brain
brain
of fetal at
at20
brain atweeks’
20 weeks’
20 gestation:
weeks’gestation: (a)
(a)multiplanar
gestation: multiplanar
(a) analysis
analysis
multiplanar after
analysis a avolume
after
aftervolume
a volume
acquisition
acquisition
acquisition with
with corpus
corpus
with corpus callosum
callosum
callosummode
modemodethrough
through
throughtheanterior
the anterior
the partof
part
anterior of the
the
part sagittal
ofsagittal
the suture
suture
sagittal showing
showing
suture corpus
corpus
showing callosum
callosum
corpus (CC),
(CC),
callosum and
(CC),
and
and(b)(b)
multiplanar
multiplanaranalysis after
analysis a volume
after a volumeacquisition
acquisition through
throughthe the
posterior fontanelle
posterior showing
fontanelle corpus
showing callosum
corpus (CC),(CC),
callosum
(b) multiplanar analysis after a volume acquisition through the posterior fontanelle showing corpus callosum (CC), cavum
cavum septi pellucidi (C.S.P.), thalamus (TH), brainstem (BS), and cerebellar vermis (CV).
cavum
septi septi(C.S.P.),
pellucidi pellucidi (C.S.P.),(TH),
thalamus thalamus (TH), brainstem
brainstem (BS), and vermis
(BS), and cerebellar cerebellar vermis (CV).
(CV).
After a 3D volume acquisition of the fetal spine at mid-sagittal plane, a rendered view
After
After a 3Da 3D volume
volume acquisition
acquisition of of
thethe fetal
fetal spine
spine at at mid-sagittal
mid-sagittal plane,
plane, a rendered
a rendered view
view
of the fetal spine can be well displayed with various modes (Figure 8a,b). In addition, the
of of
the fetal
the fetalspine
spinecan
canbebewell
welldisplayed
displayed with
with various modes (Figure
(Figure 8a,b).
8a,b).InInaddition,
addition,the
coronal planes at the level of the vertebral bodies and/or posterior arches can be recon-
thecoronal
coronal planes
planes at at
thethe level
level of of
thethe vertebral
vertebral bodies
bodies and/or
and/or posterior
posterior arches
arches canrecon-
can be be
structed on multiplanar analysis [5].
reconstructed on multiplanar
structed on multiplanar analysis
analysis [5].[5].
(a) (b)
(a) (b)
Figure 8. Three-dimensional rendered views of fetal spine at 20 weeks’ gestation after a volume acquisition with skeletal
Figure
mode: (a)8. Three-dimensional
usual mode, and (b) rendered
X-ray
Figure views of fetal spine
8. mode.
Three-dimensional at 20 weeks’
rendered gestation
views of afterata 20
fetal spine volume acquisition
weeks’ gestation with
afterskeletal
a volume
mode: (a) usual mode, and (b) X-ray mode.
acquisition with skeletal mode: (a) usual mode, and (b) X-ray mode.
5.2. Spatiotemporal Image Correlation
5.2. Spatiotemporal
5.2. Image
Spatiotemporal
Spatiotemporal Correlation
Image
Image Correlation
Correlation (STIC) allows an automatic acquisition of a single
Spatiotemporal
3D volumeSpatiotemporal Image
through slowImage Correlation
sweepCorrelation(STIC)
(STIC)
and subsequent allows
allowsanan
analysisautomatic
automatic
in a loopedacquisition
acquisitionof of
cine sequencya single
a of
single
3D volume
3D volume
images through slow sweep
through slow sweep and
in the multiplanar/multi-sliceand subsequent
subsequent
format analysis in a
analysisview.
and a rendered looped
in a This
loopedcine sequency
cancine im-of of
sequency
produce
images
images
ages in the multiplanar/multi-slice
in the multiplanar/multi-slice
in a standardized format and
format and
plane while minimizing a rendered view. This
a rendereddependency
the operation can produce
view. This can images
produce
of the ultra- im-
in ages
a standardized
sound examination. plane
in a standardized while
The recent minimizing
planeadvances the operation
in gray
while minimizing scale and
the dependency
color
operationDoppler of theprocessing
post
dependency ultrasound
of the ultra-
examination. The recentThe
sound examination. advances
recent in gray scale
advances in and
graycolor
scaleDoppler
and colorpost processing
Doppler postimproves
processing
Diagnostics 2021, 11, x FOR PEER REVIEW 10 of 18
Diagnostics 2021, 11, 1217 10 of 18
improves
the display the display ofimages.
of ultrasound ultrasound
Usingimages. Using color
color Doppler Doppler
with STIC in thewith STIC inmode
glass-body the glass-
can show normal and abnormal anatomy of the fetal heart and major vessels [46] (Figure vessels
body mode can show normal and abnormal anatomy of the fetal heart and major 9,
[46] (Figure
Video S9). The9,matrix
Videoprobe
S9). The matrix
allows probeacquisition
the rapid allows theof rapid acquisition
an STIC volume,of an reducing
thus STIC volume,
thus
the reducing
motion theand
artifact motion artifactlive
facilitating and4Dfacilitating liveIn4D
display [46]. displaythe
addition, [46].
useInofaddition, the use
the matrix
of theallows
probe matrixtheprobe allows the
simultaneous simultaneous
examination examination
of two orthogonalofplanes
two orthogonal
of the fetal planes
heart inof the
the ‘biplane
fetal heart mode’. Additional
in the ‘biplane use ofAdditional
mode’. image recognition software
use of image can help review
recognition cardiac
software can help
structures in the standard planes [46]. The 3D rendered images are useful for
review cardiac structures in the standard planes [46]. The 3D rendered images are useful counseling
tofor
parents. In addition,
counseling STIC
to parents. volume can
In addition, STICfacilitate
volumeinterdisciplinary consultation and
can facilitate interdisciplinary consul-
teleconsultation [42].
tation and teleconsultation [42].
Figure9.9.Color
Figure ColorDoppler
Doppler with
with spatiotemporal
spatiotemporal image
image correlation
correlation inglass-body
in the the glass-body
modemode showing
showing
multiplanar view and a rendered image of a normal fetal heart at 20 weeks’ gestation.
multiplanar view and a rendered image of a normal fetal heart at 20 weeks’ gestation.
5.3.
5.3.3D
3DUltrasound
UltrasoundExamination
Examinationof Face, Limbs,
of Face, andand
Limbs, Other Structures
Other Structures
While
While2D 2Dultrasound
ultrasound is aiskey tool
a key forfor
tool thethe
detection of fetal
detection anomalies,
of fetal therethere
anomalies, are some
are some
anomalies such as facial clefts, micrognathia, and club foot in which 3D
anomalies such as facial clefts, micrognathia, and club foot in which 3D ultrasound ultrasound may may
provide
provideadditional
additional information
information or or
help counseling
help when
counseling whensuchsuch
anomaly is suspected
anomaly [9]. [9].
is suspected
Compared to 2D ultrasound alone, combined approach of 2D and 3D ultrasound with
Compared to 2D ultrasound alone, combined approach of 2D and 3D ultrasound with
multiplanar/multi-slice analysis can improve the detection or exclusion of cleft palate
multiplanar/multi-slice analysis can improve the detection or exclusion of cleft palate in
in fetuses with cleft lip [50] (Figure 10). Although 3D ultrasound is less sensitive for the
fetuses with cleft lip [50] (Figure 10). Although 3D ultrasound is less sensitive for the de-
detection of isolated cleft palate, a recent study showed that an accurate evaluation of palate
tection of
requires 3Disolated
ultrasoundcleftexamination
palate, a recent
withstudy
volume showed that an
acquisition in aaccurate evaluation
strictly axial of palate
transverse
requires 3D ultrasound examination with volume acquisition in a strictly
view of the palate [16]. The use of 3D ultrasound multiplanar analysis and 3D rendering axial transverse
viewcan
view of facilitate
the palate [16].
the The of
display use of 3D ultrasound
mid-sagittal plane ofmultiplanar
the fetal faceanalysis
and thusand 3D rendering
improve the
view canoffacilitate
accuracy the display
measurements of the of mid-sagittal
mandible plane
and the of theof
detection fetal face and thus
micrognathia [51].improve the
accuracy of measurements
Three-dimensional (3D) of the mandible
rendering and the
technology withdetection of micrognathia
skeletal mode can display[51].
skull,
vertebrae, ribs, long bones and fingers [52] (Figure 11a,b and Video S10a,b). Prenatal as-
sessment of the ribs and vertebral pattern can be performed by 3D ultrasound with skeletal
mode (Figure 8a,b), albeit it is not a routine practice. A review of 39 studies including
75,018 healthy subjects and 6130 subjects with structural or chromosomal anomalies or
adverse outcome showed an association between cervical ribs and other structural anoma-
lies including esophageal atresia and anorectal malformation [53]. Abnormalities such as
craniosynostosis [26,54], and extra ribs can be shown.Diagnostics
Diagnostics 2021,
2021, 11,11, x FOR PEER REVIEW
1217 11ofof1818
11
Figure 10. Three-dimensional ultrasound assessment of the fetal face at 13 weeks’ gestation s
multiplanar views of lip and palate (reference dot).
Three-dimensional (3D) rendering technology with skeletal mode can display
vertebrae, ribs, long bones and fingers [52] (Figure 11a,b and Video S10a,b). Prena
sessment of the ribs and vertebral pattern can be performed by 3D ultrasound wit
etal mode (Figure 8a,b), albeit it is not a routine practice. A review of 39 studies inc
75,018 healthy subjects and 6,130 subjects with structural or chromosomal anoma
adverse outcome showed an association between cervical ribs and other structural
Figure10.
Figure 10.Three-dimensional
Three-dimensional
alies includingultrasound assessment
esophageal
ultrasound atresiaofof
assessment andthefetal
the fetalface
anorectalfaceatat
1313weeks’
weeks’gestation
malformation gestation showing
[53].showing
Abnormalities s
multiplanar views of lip and palate (reference dot).
multiplanar viewscraniosynostosis [26,54], and
of lip and palate (reference extra ribs can be shown.
dot).
Three-dimensional (3D) rendering technology with skeletal mode can display skull,
vertebrae, ribs, long bones and fingers [52] (Figure 11a,b and Video S10a,b). Prenatal as-
sessment of the ribs and vertebral pattern can be performed by 3D ultrasound with skel-
etal mode (Figure 8a,b), albeit it is not a routine practice. A review of 39 studies including
75,018 healthy subjects and 6,130 subjects with structural or chromosomal anomalies or
adverse outcome showed an association between cervical ribs and other structural anom-
alies including esophageal atresia and anorectal malformation [53]. Abnormalities such as
craniosynostosis [26,54], and extra ribs can be shown.
(a) (b)
Figure 11. Three-dimensional rendered images
Figure 11. Three-dimensional of theimages
rendered fetal skeleton
of the at 20–22
fetal weeks’atgestation
skeleton showing:
20–22 weeks’ (a) X-ray mode
gestation
the skull bone with frontal
showing: suture
(a) X-ray mode(SS) andskull
of the anterior
bonefontanelle (AF),
with frontal and(SS)
suture (b) and
HD anterior
skeletal fontanelle
mode of the skull,
(AF), andbones of t
upper and (b)
lower limbs.
HD skeletal mode of the skull, bones of the upper and lower limbs.
It is difficult to It is difficult
visualize to visualize
esophagus on 2Desophagus
ultrasoundon 2D ultrasound
examination. Theexamination.
use of 3D ul- The use
ultrasound with
trasound with multiplanar multiplanar
analysis and Crystal analysis and Crystal
Vue rendering may Vue
make rendering may make the vis
the visualization
tion possible [55]. (3D)
possible [55]. Three-dimensional Three-dimensional
volumes are acquired(3D) volumes are acquiredsection
from a midsagittal from aofmidsagit
the thorax
(a) and tion
upperof the thorax
abdomen and
with upper
the fetusabdomen
lying in with
supine
(b) the fetus
position.lying in supine position.
While 2D ultrasound Whileexamination
2D ultrasound with examination
gray scale and with gray
color scale
flow andstandard
is the color flow
for is
thethe stand
Figure 11. Three-dimensional rendered images
antenatal diagnosis of the fetal
of placenta
the antenatal skeleton at 20–22
accreta spectrum
diagnosis weeks’
of placenta gestation
disorders
accreta[22], showing: (a)
3D ultrasound
spectrum X-ray mode
disorderswith of
[22],power
3D ultrasoun
the skull bone with frontalDoppler
suture (SS)
andand anterior fontanelle
multiplanar analysis(AF), and an
permits (b) accurate
HD skeletal mode of the
assessment skull,
of the bones of the
placenta-bladder
upper and lower limbs. interface, and the degree of bladder invasion by the placenta [56]. Three-dimensional (3D)
rendered images can be used for patient counseling [56].
It is difficult to visualize esophagus on 2D ultrasound examination. The use of 3D
ultrasound
5.4. 3D Printing with multiplanar analysis and Crystal Vue rendering may make the visualiza-
tionWith
possible [55]. Three-dimensional
advances in 3D ultrasound, (3D) volumesultrasound
the derived are acquired from
data canabe midsagittal
used for 3D sec-
tion of the thorax and upper abdomen with the fetus lying in supine
printing of physical models of whole fetuses [57] and the fetal face [58]. A recent trial position.
showed While
that2Dtheultrasound examination
use of 3D-printed fetalwith gray
facial scale and
models colorin
resulted flow is theincreases
greater standard in for
the antenatal diagnosis of placenta accreta spectrum disorders [22], 3D ultrasound with5.4. 3D Printing
With advances in 3D ultrasound, the derived ultrasound data can be used for 3D
printing of physical models of whole fetuses [57] and the fetal face [58]. A recent tria
Diagnostics 2021, 11, 1217 showed that the use of 3D-printed fetal facial models resulted in greater increases 12 of 18 in ma
ternal–fetal attachment in the third trimester than the use of ultrasonography only [58
Whether this can be translated into better pregnancy outcomes needs further studies. I
maternal–fetal attachment in the third trimester than the use of ultrasonography only [58].
addition,
Whether a 3D-printed
this spinainto
can be translated bifida model
better can beoutcomes
pregnancy beneficial for surgical
needs rehearsal
further studies. In prior t
a fetoscopic repair [59].
addition, a 3D-printed spina bifida model can be beneficial for surgical rehearsal prior to a
Withrepair
fetoscopic advances
[59]. in STIC, the derived data can be used for 3D printing of the fetal hear
which Withisadvances
a fast-moving
in STIC,structure
the derived [60].
dataIncan
a recent
be usedcase
for 3Dreport, theofauthors
printing the fetalfound
heart, that th
which
3D model was useful in showing the complex anatomy of fetal transposition 3D
is a fast-moving structure [60]. In a recent case report, the authors found that the of great ar
model
terieswasanduseful in showing
in providing the complex
prenatal parentalanatomy of fetal[61].
counseling transposition of great arteries
and in providing prenatal parental counseling [61].
Previously, after acquisition of a 3D/STIC volume dataset, a number of post-pro
Previously, after acquisition of a 3D/STIC volume dataset, a number of post-processing
cessing steps are required to convert it from Cartesian.vol file through segmentation, re
steps are required to convert it from Cartesian.vol file through segmentation, refinement,
finement,
and and optimization
optimization to a STL (Standard to a Triangle
STL (Standard
Language) Triangle Language)
file, the industry file, the
standard file industr
type for 3D Printing [60]. These steps take a long time, and whether the final produced STL the fina
standard file type for 3D Printing [60]. These steps take a long time, and whether
produced
file STL fileforis3D
is good enough good enough
printing is notfor 3D printing
certain is not certain
before processing. With before processing. Wit
recent advances
recent
in advances
ultrasound in ultrasound
technology, a 3D/STIC technology, a 3D/STIC
volume dataset can bevolume
directly dataset
exportedcanfrombethedirectly ex
ultrasound machine as an STL file that is ready for viewing on a personal
ported from the ultrasound machine as an STL file that is ready for viewing on a persona computer using
common
computer software
using as well as for
common 3D printing
software as well(Figure 12).
as for 3D printing (Figure 12).
Figure12.12.
Figure AA physical
physical model
model of three-dimensional
of three-dimensional printing
printing of the
of the fetal fetal face.
face.
6.6.FetalHQ
FetalHQ
FetalHQ, a novel heart and vascular analysis software, can allow assessment of the
FetalHQ, a novel heart and vascular analysis software, can allow assessment of th
fetal heart shape, size, and contractibility by using speckle tracking to analyze the motion of
fetal heart shape, size, and contractibility by using speckle tracking to analyze the motio
multiple points of the fetal heart [62] (Figure 13). The global sphericity index (SI) is a simple
of multiple points
measurement of the
of cardiac fetal heart
contractility, and[62] (Figure
it is 13).
equal to The global mid-basal–apical
(end-diastolic sphericity index (SI) is
length)/transverse length [63]. For 24-segment sphericity index, SI is computed for each mid-basal
simple measurement of cardiac contractility, and it is equal to (end-diastolic of
apical
the length)/transverse
24 end-diastolic length
transverse [63]. which
segments, For 24-segment sphericity
are distributed from theindex, SIthe
base to is computed
apex fo
ofeach
eachofventricle, as well as the end-diastolic
the 24 end-diastolic mid-basal–apical
transverse segments, whichlength [62].
are distributed from the base t
the This
apex24-segment sphericity
of each ventricle, as index is athe
well as comprehensive
end-diastolicmethod to assess thelength
mid-basal–apical shape of
[62].
ventricular chambers [62]. The SI for each segment was independent of gestational age
and fetal biometry. The SI of the right ventricle was lower than that of the left ventricle
for segments 1–18. This index can be used when discordance between the size of the atrial
and/or ventricular cardiac chambers is found. Abnormal SI values are found in the fetuses
with cardiac abnormalities such as coarctation of aorta, pulmonary stenosis, and fetal
growth restriction [62]. Abnormal SI values are associated with increased risk of perinatal
complications and childhood and/or adult cardiovascular disease [64].Diagnostics2021,
Diagnostics 2021,11,
11,1217
x FOR PEER REVIEW 13 of18
13 of 18
Figure13.
Figure 13.FetalHQ
FetalHQassessment
assessment of
ofthe
thefetal
fetalheart
heartshape,
shape,size,
size,and
andcontractibility
contractibilityby
byusing
usingspeckle
speckle
tracking to analyze the motion of multiple points of the fetal heart at 20 weeks’ gestation.
tracking to analyze the motion of multiple points of the fetal heart at 20 weeks’ gestation.
This 24-segment
While sphericity
the initial results index is aacomprehensive
are promising, recent review ofmethod
23 studies to showed
assess the shape of
conflicting
ventricular chambers [62]. The SI for each segment was independent
results concerning the development of strain and strain rate during gestation [65]. Large of gestational age
and fetal biometry. The SI of the right ventricle was lower than that
longitudinal cohort studies with a standard protocol are needed to obtain reference values of the left ventricle for
segments
for 1–18. This
fetal cardiac index caninbe
deformation used when discordance
uncomplicated pregnancies between
[65]. Athe size of
recent the atrial
systematic
and/or ventricular cardiac chambers is found. Abnormal SI values
review also showed heterogeneous results concerning gestational age and Doppler profiles. are found in the fetuses
with cardiac abnormalities such as coarctation of aorta, pulmonary
Large prospective longitudinal cohort studies are required to assess the clinical significance stenosis, and fetal
growth restriction [62]. Abnormal SI values are associated with
of deformation measurements of the fetal heart in growth restricted fetuses and normal increased risk of perinatal
complications
fetuses [66]. and childhood and/or adult cardiovascular disease [64].
While the initial results are promising, a recent review of 23 studies showed conflict-
7.ing
Artificial
results Intelligence
concerning the development of strain and strain rate during gestation [65].
Large longitudinal
Machine learning,cohort studies with
in particular deepa standard
learning,protocol are neededimage
allows ultrasound to obtain reference
recognition
and thus facilitates the automatic identification and measurement of fetal biometry system-
values for fetal cardiac deformation in uncomplicated pregnancies [65]. A recent [67]. It
isatic reviewofalso
a branch showed
artificial heterogeneous
intelligence (AI). In results concerning
obstetric gestationalthe
ultrasonography, age and Doppler
automation of
profiles. Largeof
measurements prospective
fetal biometry longitudinal cohort useful
is a potentially studiestool
are to
required
increasetothe assess the clinical
reliability and
significance ofof
reproducibility deformation
measurements measurements
as comparedoftothe fetal measurements
manual heart in growth restricted
[68]. fetuses
In addition, it
andreduce
can normal fetuses [66].
scanning time [68] and work-related fatigue and musculoskeletal disorders [69].
With automatic image recognition technology applied on a frozen 2D ultrasound
7. Artificial
image, Intelligence of fetal biometry including biparietal diameter (BPD), head
auto measurement
circumference
Machine (HC),learning,abdominal circumference
in particular (AC),allows
deep learning, and femur length (FL)
ultrasound image becomes fea-
recognition
sible.
and thusA study showed
facilitates the aautomatic
success rate of 91.43% and
identification and 100% for auto of
measurement measurement
fetal biometry of HC
[67].
and
It is BPD, respectively
a branch of artificial [67]. Although(AI).
intelligence the Ininaccuracy for the plane acceptance
obstetric ultrasonography, check for
the automation of
head parameters was 12.9% [67], such inaccuracy can be corrected
measurements of fetal biometry is a potentially useful tool to increase the reliability by fine-tuning of the
and
caliper placement
reproducibility ofmanually.
measurements In another study, manual
as compared to manualadjustment
measurementsof caliper[68].position was
In addition,
not required in about two-thirds of cases for HC and FL measurements,
it can reduce scanning time [68] and work-related fatigue and musculoskeletal disorders but it was required
in more than 80% for the measurement of AC [68]. Auto measuring AC is more difficult
[69].
than measuring
With automatic HC because of the low contrast
image recognition technology between
appliedtheonabdomen
a frozen 2D andultrasound
surrounding im-
tissues and the large variability in abdominal shape and appearance [68]. The accuracy of
age, auto measurement of fetal biometry including biparietal diameter (BPD), head cir-
the auto measurement of HC, AC, and FL was high, and it compared well with previously
cumference (HC), abdominal circumference (AC), and femur length (FL) becomes feasi-
published manual-to-manual agreement, but the auto measurements had a tendency to
ble. A study showed a success rate of 91.43% and 100% for auto measurement of HC and
underestimate biometry, which requires further improvements in the algorithm [68].
BPD, respectively [67]. Although the inaccuracy for the plane acceptance check for head
With automatic image recognition technology applied on an acquired 3D ultrasound
parameters was 12.9% [67], such inaccuracy can be corrected by fine-tuning of the caliper
volume of the fetal head from the BPD plane, SonoCNS allows auto measurement of fetal
placement manually. In another study, manual adjustment of caliper position was not re-
biometry including BPD, HC, atrium of the posterior horn of the lateral ventricle (Vp),
quired in about two-thirds of cases for HC and FL measurements, but it was required in
transcerebellar diameter (TCD), and cisterna magnum (CM) [70] (Figure 14). A recent
more than 80% for the measurement of AC [68]. Auto measuring AC is more difficult than
study showed that this 3D automated technology reliably identified and measured BPD
measuring HC because of the low contrast between the abdomen and surrounding tissues
and the large variability in abdominal shape and appearance [68]. The accuracy of the autolished manual-to-manual agreement, but the auto measurements had a tendency to un-
derestimate biometry, which requires further improvements in the algorithm [68].
With automatic image recognition technology applied on an acquired 3D ultrasound
volume of the fetal head from the BPD plane, SonoCNS allows auto measurement of fetal
Diagnostics 2021, 11, 1217 biometry including BPD, HC, atrium of the posterior horn of the lateral ventricle 14 (Vp),
of 18
transcerebellar diameter (TCD), and cisterna magnum (CM) [70] (Figure 14). A recent
study showed that this 3D automated technology reliably identified and measured BPD
and
andHCHCbut
butwas
wasless
lessso
sofor
forTCD,
TCD,CM,
CM,and
andVp
Vp[70].
[70].Further
Furtheroptimization
optimizationofofthis
thisautomated
automated
technology
technologyisisrequired.
required.
Figure14.
Figure 14. SonoCNS,
SonoCNS, after
after volume
volume acquisition
acquisition of
of the
the fetal
fetalbrain
brainatatbiparietal
biparietaldiameter
diameterplane
planeatat21
weeks gestation, showing auto measurement of biparietal diameter (BPD), head circumference
21 weeks gestation, showing auto measurement of biparietal diameter (BPD), head circumference
(HC), atrium of the posterior horn of the lateral ventricle (Vp), transcerebellar diameter (TCD), and
(HC), atrium of the posterior horn of the lateral ventricle (Vp), transcerebellar diameter (TCD), and
cisterna magnum (CM).
cisterna magnum (CM).
Fetal Intelligent Navigation Echocardiography (FINE) applied on a STIC volume us-
Fetal Intelligent Navigation Echocardiography (FINE) applied on a STIC volume
ing “intelligent navigation” technology allows the automatic display of nine standard fe-
using “intelligent navigation” technology allows the automatic display of nine standard
tal echocardiography views [71]. This can simplify fetal cardiac examinations, reduce op-
fetal echocardiography views [71]. This can simplify fetal cardiac examinations, reduce
erator dependency,
operator dependency,and andhelp
helpdetect
detectcongenital
congenitalheart heartdefects
defects[71].[71].
During a real-time 2D morphology scan,
During a real-time 2D morphology scan, identifying and identifying andinterpreting
interpretingfetalfetalstandard
standard
scan planes are highly complex tasks. With automatic image
scan planes are highly complex tasks. With automatic image processing technology [46,70], processing technology
[46,70],
these these
tasks cantasks can beby
be assisted assisted by providing
providing feedback or feedback
guidance or to
guidance to an ultrasound
an ultrasound operator
operator on whether a correct standard scan plane of fetal anatomy
on whether a correct standard scan plane of fetal anatomy is obtained, whether all parts is obtained, whetherof
all partsare
anatomy of anatomy
checked, andare checked, and whether
whether unusual unusual
findings findingsplane
on a standard on a standard plane
are identified are
[72].
The operator can use this technology as a second pass or confirmation to improve diagnosticto
identified [72]. The operator can use this technology as a second pass or confirmation
improve[70].
accuracy diagnostic
This canaccuracy [70].audit
also allow This can
andalso allow
quality audit and quality
improvement [73]. improvement [73].
Based on deep learning, image segmentation is an image
Based on deep learning, image segmentation is an image processing method processing methodthat thatcancan
automatically recognize the location and size of an object in
automatically recognize the location and size of an object in pixels. However, accurate pixels. However, accurate
segmentationofofmost
segmentation mostanatomical
anatomicalstructures
structuresininmedical
medicalultrasound
ultrasoundisislimitedlimitedby bythethelow
low
contrastbetween
contrast betweenthe thetarget
targetand
andbackground
background ofof
thethe images
images [74].
[74]. ToTo improve
improve thethe segmen-
segmenta-
tation
tion performance
performance of of
thethe thoracic
thoracic wall
wall in in fetal
fetal ultrasound
ultrasound videos,a anovel
videos, novelmodel-agnostic
model-agnostic
methodusing
method using deep
deep learning
learning techniques
techniques in processing
in processing time-series
time-series information
information of ultra-
of ultrasound
sound videos and the shape of the thoracic wall was proposed
videos and the shape of the thoracic wall was proposed [75]. Accurate segmentation can [75]. Accurate segmenta-
tion ultrasonographers
assist can assist ultrasonographers with the
with identifying identifying the thoracic
thoracic area area and its
and its orientation, andorientation,
it has the
and it has
potential tothe
buildpotential
AI-based to build AI-based
diagnostic supportdiagnostic
modelssupport
to assess models to assessview
four-chamber four-cham-
[75].
ber There
view [75].
are emerging studies on the application of artificial intelligence in obstetric
There
scan. It are emerging
is feasible to use 3D studies on thetoapplication
ultrasound automatic measureof artificial intelligence
thymic volume in obstetric
[76]. Two-
dimensional (2D) placental
scan. It is feasible to use 3Dsonographic
ultrasound to images can bemeasure
automatic screened for lacunae,
thymic volumewhich is a
[76]. Two-
feature of PAS [77]. Preliminary results are encouraging. Further
dimensional (2D) placental sonographic images can be screened for lacunae, which is a improvement of algorithm
and technology are required prior to using AI applications in clinical practice.
8. Conclusions
The use of high-resolution ultrasonography can facilitate detailed diagnostic ultra-
sonography, in particular, fetal echocardiography and targeted neurosonography, in at-risk
pregnancies, as suggested by the recent guidelines. The use of radiant flow can improve
the display, especially in complex cardiac or vascular structures. The use of 3D/4D ul-You can also read
