Download Real-time three-dimensional foetal echocardiography using a new

Archives of Cardiovascular Disease (2014) 107, 4—9
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CLINICAL RESEARCH
Real-time three-dimensional foetal
echocardiography using a new
transabdominal xMATRIX array transducer
Échocardiographie cardiaque fœtale 3D temps réel par voie
trans-abdominale avec une nouvelle sonde matricielle
Philippe Acar a,∗, Laia Battle b, Yves Dulac a,
Marianne Peyre a, Hélène Dubourdieu b,
Sébastien Hascoet a, Marion Groussolles b,
Christophe Vayssière b
a
Department of Paediatric Cardiology, Children’s Hospital, 330, avenue de Grande-Bretagne,
31059 Toulouse cedex 9, France
b
Department of Obstetrics and Gynaecology, Mother’s Hospital, Toulouse, France
Received 5 August 2013; received in revised form 18 October 2013; accepted 24 October 2013
Available online 22 December 2013
KEYWORDS
Fetal
echocardiography;
2D echocardiography;
3D echocardiography;
Congenital heart
defect;
STIC
Summary
Background. — Foetal echocardiography has been used to diagnose congenital heart disease.
However, conventional echocardiography can only display two-dimensional (2D) structural
images of the intricate three-dimensional (3D) foetal heart.
Aim. — The purpose of this study was to report the first use of a new transabdominal xMATRIX
array transducer and to describe its ability to perform all 3D modalities: intelligent spatiotemporal image correlation (iSTIC) acquisition, xPlane imaging and 3D surface imaging.
Methods. — Eighty foetuses without congenital heart disease were included consecutively, with
a gestational age between 20 and 37 weeks. 2D and 3D scans were performed with a transabdominal xMATRIX array transducer. Cardiac-STIC volume datasets were acquired and postprocessed
with new automatic software (the ‘Fetal Heart Navigator’).
Results. — A total of 224 iSTIC acquisitions were performed (mean time for each, 2 seconds).
Only 78 iSTIC acquisitions (35%) were able to detect the ductal arch automatically. ‘Fetal Heart
Navigator’ feasibility varied according to foetal position, including the descending aorta. Live
Abbreviations: 2D, two-dimensional; 3D, three-dimensional; CHD, congenital heart disease; FHN, ‘Fetal Heart Navigator’; iSTIC, intelligent spatiotemporal image correlation; STIC, spatiotemporal image correlation.
∗ Corresponding author.
E-mail address: acar.p@chu-toulouse.fr (P. Acar).
1875-2136/$ — see front matter © 2013 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.acvd.2013.10.003
Real-time 3D foetal echo
5
xPlane imaging had excellent feasibility regardless of foetal position; using rotation, lateral
and vertical tilts, all cardiac structures were identified from a unique reference plane. Live
3D surface imaging had variable feasibility depending on the target structure. Only 10% of the
volume dataset offered comprehensive imaging of intracardiac views.
Conclusion. — The new xMATRIX transabdominal transducer allows a multimodality approach to
the foetal heart. Further studies that include foetuses with cardiac malformations are required.
© 2013 Elsevier Masson SAS. All rights reserved.
MOTS CLÉS
Échocardiographie
fœtale ;
Échocardiographie
2D ;
Échocardiographie
3D ;
Cardiopathie
congénitale ;
STIC
Résumé
Contexte. — L’échocardiographie fœtale permet de dépister les malformations cardiaques chez
le fœtus. Néanmoins, les ultrasons conventionnels sont limités à des coupes 2D.
Objectif. — Notre but a été de rapporter la 1re utilisation d’une sonde matricielle 3D transabdominale chez le fœtus.
Méthodes. — Quatre-vingt fœtus sans malformations cardiaque d’âge gestationnel de 20 à
37 semaines d’aménorrhée ont été inclus incluant des acquisitions 2D et 3D (iSTIC, xPlan et
imagerie de surface 3D). Un nouveau processeur automatique des données STIC (fetal heart
navigator) a été utilisé.
Résultats. — Deux cent vingt-quatre acquisitions iSTIC ont été réalisées (temps moyen de deux
secondes). Seulement 78 acquisitions iSTIC (35 %) ont été exploitables par le fetal heart navigator (nécessité d’inclure l’aorte descendante). Le xPlan avait une bonne faisabilité indépendante
de la position du fœtus. À partir d’une image de référence, après rotation ou inclinaison latérale
et verticale tilts, toutes les structures cardiaques ont pu être identifiées. L’imagerie de surface
3D n’a donné une image exploitable que dans 10 % des fœtus.
Conclusion. — La nouvelle sonde matricielle xMATRIX transabdominale permet une approche
multimodale du cœur fœtal. D’autres études sont nécessaires pour démontrer son intérêt dans
le dépistage des malformations cardiaques.
© 2013 Elsevier Masson SAS. Tous droits réservés.
Background
Congenital heart disease (CHD) is one of the most common
congenital anomalies and is the leading cause of neonatal and infant mortality. Prenatal diagnosis of CHD has
benefits for parental counselling, decision making during
pregnancy, prenatal interventions, site and mode of delivery, and postnatal management [1]. The detection rate
of prenatal cardiac lesions has increased significantly during the past two decades with the improvement in foetal
echocardiography [2]. Two-dimensional (2D) foetal echocardiography has been used to screen, diagnose, monitor and
treat congenital heart defects and rhythm abnormalities
[3]. However conventional echocardiography can only display 2D structural images of the intricate three-dimensional
(3D) foetal heart. 3D echocardiography has been shown to
enhance the diagnosis of CHD in children [4,5]. Spatiotemporal image correlation (STIC) was first introduced for 3D foetal
echocardiography using mechanical transducers [6,7]. STIC
acquires a series of volume data that can be displayed in
any plane. However, postprocessing of the volume dataset
requires expertise [8,9]. Real-time 3D echocardiography in
the foetus was recently introduced with the development
of the cardiac xMATRIX array transducer [10,11]. This type
of transducer enables visualization and examination of the
pulsating foetal heart in real time, without the need for gating, and is unaffected by motion artefacts. Live 3D surface
and xPlane imaging are modalities of this new technology
[12]. However, STIC and live 3D imaging have never been
produced by the same ultrasound system.
We report for the first time on a new transabdominal xMATRIX array transducer. Our aim was to describe its ability to
perform the three modalities of 3D imaging: STIC acquisition, xPlane imaging and 3D surface imaging. New automatic
software for displaying STIC planes was tested.
Methods
Eighty women with singleton pregnancies (gestational age
between 20 and 37 weeks) were studied consecutively at
Toulouse University Hospital from July to October 2012. All
patients had undergone previous 2D ultrasound examinations that excluded any malformations. Informed consent
was obtained in all cases.
Transabdominal real-time 3D echocardiography was performed using an iU22 ultrasound machine (Philips Medical
Systems, Bothell, WA, USA) equipped with an x6-1 PureWave
xMATRIX array transducer (Fig. 1). All 3D echocardiography
was performed by two experienced operators (P.A. and C.V.).
Three modalities of 3D imaging were performed.
Intelligent STIC (iSTIC) acquisition
With the full volume angle set at 20◦ and an acquisition time
of only 3 seconds, this fast acquisition is obtained thanks
to the electronic phasing of the x6-1 xMATRIX transducer
(versus 10 seconds with the conventional STIC method on a
mechanical transducer). The acquisition was started from
a four-chamber view during a foetal quiescent period. Two
to three sets of volume data were collected for each case
6
P. Acar et al.
and saved on the hard disk of the machine. All volume
datasets were analysed off-line using dedicated software
by two independent observers (L.B. and M.G.). Postprocessing was performed using the ‘Fetal Heart Navigator’ (FHN)
software (plug-in within QLAB 9.0 software; Philips Medical Systems, Bothell, WA, USA; 2011). The FHN software
automatically detects the ductal arch as the initial view no
matter what position the iSTIC data set or STIC data set is
acquired in (Fig. 2). For the next step, the user was guided in
obtaining the views recommended by the ISUOG guidelines
on foetal cardiac screening: the four-chamber view and the
left and right ventricular outflow tract views [3]. At the end
of the protocol, all four views were displayed on one screen.
Figure 1. x6-1 PureWave xMATRIX array transducer containing
9000 active elements (35 times more elements than conventional
transducers), allowing different imaging modes, such as iSTIC acquisition, live xPlane imaging and live 3D imaging.
Live xPlane imaging
The xMATRIX array transducer allows the simultaneous display by using a split-screen format of two high-resolution
real-time views: a primary reference imaging plane and a
secondary imaging plane selected by electronic rotation of
the ultrasound beam (Fig. 3). A rotation through a full 360◦
Figure 2. A. ‘Fetal Heart Navigator’: acquisition with the x6-1 xMATRIX array transducer on the iU22 ultrasound system (Philips Medical
Systems, Bothell, WA, USA) on the normal heart of a 24-week foetus. Extraction of the four-chamber view (1), left ventricular outflow tract
(2), right ventricular outflow tract (3) and ductal arch (4). B. ‘Fetal Heart Navigator’: acquisition with the x6-1 xMATRIX transducer on the
iU22 ultrasound system on the normal heart of a 30-week foetus. The system cannot find the required ductal arch view.
Real-time 3D foetal echo
7
Figure 4. Live 3D imaging with the x6-1 xMATRIX array transducer
on the iU22 ultrasound system (Philips Medical Systems, Bothell,
WA, USA) of the normal heart of a 30-week foetus. Extraction of
the four-chamber view in a volume.
Analysis was performed by two independent observers (Y.D.
and S.H.).
Results
Figure 3. A. xPlane with lateral tilt selected of the normal heart
of a 30-week foetus. Left image (the acquisition view): ventricular short-axis view. Right image: real-time lateral view (scan plane
demonstrated by the white line bisecting the left view). B. xPlane
with lateral tilt selected of the normal heart of a 20-week foetus.
Left image (the acquisition view): right ventricular outflow tract.
Right image: real-time lateral extraction view, showing the left ventricular outflow tract (demonstrated by the white line bisecting the
left image).
was applied from the reference image plane. A lateral tilt
from −45◦ to +45◦ was added to the rotated image plane.
From the reference plane, an elevation tilt was performed
from −30◦ to +30◦ .
Live 3D surface imaging
The system acquired 3D data using a 40◦ × 20◦ pyramidal
imaging volume of the target organ (Fig. 4). Two orthogonal
reference planes were used to localize cardiac structures
in the volume. Navigation by cropping inside the volume
allowed surface rendering of the intracardiac structures.
A total of 224 iSTIC acquisitions were performed in
80 foetuses. The mean time for each acquisition with the
xMATRIX array transducer was 2 seconds. All the volume
datasets were analysed using the FHN software. We defined
the feasibility of the FHN as the ability to depict the ductal
arch view from the initial acquisition. Only 78 iSTIC acquisitions were able to detect the ductal arch automatically,
resulting in a feasibility of 34.8% for FHN. Feasibility varied according to foetal position (either apical, right-sided or
left-sided insonation of the four-chamber view of the foetal
heart), including the descending aorta.
Live xPlane imaging had excellent feasibility (95%)
regardless of foetal position. Using rotation, lateral and elevation (vertical) tilts, all normal cardiac structures were
identified from a unique reference image plane: the atrial
cavity and septum; the atrioventricular valves; the ventricular cavity and septum; the left and right ventricular outflow
tracts; the ascending aorta; and the main pulmonary artery
and its bifurcation.
The feasibility of live 3D surface imaging varied depending on the target structure. Only 10% of the volume dataset
offered comprehensive imaging. By cropping and rotating
the 3D pyramid, intracardiac en face views of the atrioventricular valves were obtained, including dynamic motion.
Discussion
This is the first report using a transabdominal xMATRIX array
transducer applying all modalities of 3D imaging to the foetal
8
heart: STIC acquisition, xPlane imaging and 3D surface imaging.
iSTIC acquisition and postprocessing
STIC was first introduced for 3D foetal echocardiography
in 2003 using mechanical transducers [6]. STIC is an automated volume acquisition in which the array inside the
transducer performs a slow single sweep, recording a 3D
volume dataset. The major limitations of STIC technology
acquired with mechanical transducers are that the image
is not acquired in real time, making foetal movement a
problem during the acquisition time [7—9]. Such motion can
generate some degradation in image quality from the 2D
image.
Here, we report the first study of iSTIC acquisition performed using an electronic xMATRIX array transducer. We
acquired a high-resolution loop of volumes over a foetal cardiac cycle in only 2 seconds (as opposed to 10 seconds with
conventional STIC), unaffected by motion artefacts. Whatever the mode of STIC or iSTIC acquisition, the acquired
volume dataset needs off-line re-examination. Postprocessing of the volume dataset requires time and expertise. We
used new protocol-driven workflow FHN software. It does
not matter in which position the iSTIC or STIC data set
is acquired for the FHN software. A major limitation of
the software is the difficulty in detecting the ductal arch
(dependent on the foetal position and the acquisition box).
Feasibility could be increased by using right-sided or leftsided insonation of the four-chamber view of the foetal
heart, including the descending aorta. However by following the ISUOG guidelines, the FHN should simplify foetal
heart examination from the STIC volume [3]. Even if STIC
modalities have limited value in the foetal diagnosis of
CHD, many studies have reported its usefulness in assessing
cardiac function, atrial morphology, vessels and atrioventricular valve measurements [13—16]. STIC by telemedicine
is also a promising modality [17]. The advantage of the
xMATRIX array transducer comes from its ability to switch
to other 3D modalities, such as live xPlane and 3D surface
rendering.
Live xPlane imaging
Whereas a conventional 2D foetal echocardiogram typically
requires several minutes to obtain multiple views from different sweeps, xPlane imaging is a new mode that allows a
total scan of the foetal heart without moving the transducer.
Live xPlane imaging (or ‘biplane imaging’) is the scanning of
two image planes of the foetal heart at different angles.
The Live xPlane imaging technique does not require cardiac monitoring of the foetal cardiac cycle and avoids the
potential artefacts produced by the cardiac gating method.
Use of this method to display two cardiac planes simultaneously — namely, the four-chamber and ventricular outflow
planes — without needing to move the transducer, has been
previously described [10,18]. The rotation angle depends on
the position of the foetal heart and on the normality of the
outflow tract.
Xiong et al. reported a live xPlane imaging study in the
foetus to visualize simultaneously the four-chamber and inplane views of the interventricular septum; they concluded
P. Acar et al.
that this method may be a useful tool for the assessment
of ventricular septal defects [19]. In our study, live xPlane
imaging was able to identify a normal foetal heart with a
single position of the transducer, despite the foetus being in
a difficult position, even if we only used the lateral xPlane
view and the elevation mode available on the xMATRIX system.
Live 3D surface imaging
Live 3D surface imaging provides real-time volumetric examination of the target organ. 3D volume rendering provides
unique views of cardiac anatomical structures, which are
not easily understood on conventional 2D imaging. The use
of live 3D surface imaging has been extensively reported
in paediatric and adult cardiology; it has been shown to be
particularly useful in the assessment of valvular diseases and
CHD [4,5].
Studies using live 3D surface imaging in foetal echocardiography are still limited. We and others previously
reported that using a cardiac xMATRIX array transducer for
3D surface imaging could more precisely describe the size
of patent foramen ovale as well the location of intracardiac tumours [10,20]. Using the same xMATRIX transducer,
Xiong et al. reported the ability of the en face view of
the interventricular septum to better visualize ventricular septal defect in the foetus [21]. However, this imaging
is limited by the low penetration of the high-frequency
transducer as well as the narrow scanning angle [22]. Further studies are necessary to explore the role of this new
xMATRIX transabdominal transducer in foetal echocardiography.
Our study is the first report of live 3D surface imaging using the transabdominal xMATRIX transducer. Volume
scans are less dependent on the angle of acquisition, which
means that obtaining the requisite data may be dependent on foetal lie or operator expertise. As the resolution
of real-time 3D volume display remains inferior to that of
conventional 2D imaging, its application in foetal echocardiography is still limited [10,12—24]. Further studies are
required to compare the abilities of 3D versus 2D in foetuses
that are challenging, in terms of acoustic window and foetal
position. Moreover, these studies should include foetuses
with cardiac malformations.
As this sentence speaks to the cardiac xMATRIX transducer. Can we suggest to move it up to the position indicated
Before the sentence starting with ‘‘Further studies are necessary’’.
Disclosure of interest
The authors declare that they have no conflicts of interest
concerning this article.
Acknowledgments
Philips loaned an iU22 xMATRIX ultrasound system to
the prenatal department of the University Hospital of
Toulouse.
Real-time 3D foetal echo
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