Chaoui et al-2004-ultrasound_in_obstetrics_&amp;_gynecology

Ultrasound Obstet Gynecol 2004; 23: 535–545
Published online 6 May 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/uog.1075
Three-dimensional (3D) and 4D color Doppler fetal
echocardiography using spatio-temporal image correlation
(STIC)
R. CHAOUI, J. HOFFMANN and K. S. HELING
Unit of Prenatal Diagnosis and Therapy, Charité University Hospital, Berlin Germany
KEYWORDS: 3D; 4D; color Doppler; congenital heart defects; fetal echocardiography; spatio-temporal image correlation;
STIC
ABSTRACT
Objective Color Doppler echocardiography is used to
visualize three transverse planes: the four-chamber, five-
chamber, and three vessels and trachea views. Color
Doppler spatio-temporal image correlation (STIC) is
a new three-dimensional (3D) technique allowing the
acquisition of a volume of data from the fetal heart that is
displayed as a cineloop of a single cardiac cycle. The aim
of the study was to examine the potential of color Doppler
STIC to evaluate normal and abnormal fetal hearts.
Methods This prospective study included 35 normal
fetuses and 27 fetuses with congenital heart defects (CHD)
examined between 18 and 35 weeks of gestation. Volume
acquisition was achieved by initiating the image capture
sequence from the transverse four-chamber view. Volumes
were stored for later offline evaluation using a personal
computer-based workstation in a multiplanar mode and
as spatial volume rendering.
Results Successful acquisition was possible in all 62 cases.
The three planes could be demonstrated in 31/35 healthy
fetuses and in 24/27 fetuses with CHD. Spatial volume
rendering was attempted in 18 fetuses with CHD. In
the four normal fetuses with inadequate visualization
using color Doppler STIC, the region of interest was
perpendicular to the ultrasound beam. In two fetuses with
CHD inadequate visualization was related to an enlarged
heart in late gestation, in which the entire cardiac volume
could not be acquired. The third case was an 18-week
fetus with complex CHD and transposed great vessels in
which artifacts were related to confluent color signals as
a result of low resolution in the reconstructed plane.
Conclusions STIC in combination with color Doppler
ultrasound is a promising new tool for multiplanar and
3D/4D rendering of the fetal heart. Limitations may
be found later in gestation in fetuses with large hearts
and early in gestation as a result of low discrimination
of signals. In addition, insonation perpendicular to the
structure of interest does not image color Doppler signals
and should be avoided during acquisition. Copyright 
2004 ISUOG. Published by John Wiley & Sons, Ltd.
INTRODUCTION
An extended fetal echocardiographic examination is
achieved by acquiring and documenting sequential cross-
sectional planes1–3
. In a systematic segmental approach
the venoatrial, atrioventricular and ventriculoarterial con-
nections should be assessed to identify normal and abnor-
mal cardiac anatomy1. Several studies have demonstrated
that the increased detection of heart anomalies may be
achieved by a) understanding and implementing a system-
atic cardiac examination, b) visualizing the great vessels
in addition to the plane of the four-chamber view, and
c) using a ‘checklist’ of identified planes to exclude cardiac
malformations4
.
Color Doppler ultrasound was introduced to fetal
echocardiography in the late 1980s5
and is used by
many investigators during routine cardiac imaging to
increase the accuracy and speed of the examination6.
In a recent review we presented three transverse planes
for the routine color Doppler evaluation of the heart
and demonstrated the numerous anomalies which could
be identified in these planes6
. An examiner assessing
a number of cross-sectional cardiac planes while the
heart is beating is automatically mentally reconstructing
the heart in the third (3D) and fourth (3D + time
(4D)) dimensions. In the last decade 3D and 4D fetal
Correspondence to: Prof. R. Chaoui, Department of Obstetrics and Gynecology, Charité Medical School, Humboldt University,
Schumannstr. 20/21, D-10098-Berlin, Germany (e-mail: rabih.chaoui@charite.de)
Accepted: 6 April 2004
Copyright  2004 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER

536 Chaoui et al.
echocardiography have been investigated using external
workstations or static volume sweeps7–14
. Only a few
studies have examined the combination of color with
3D cardiac acquisition, reporting low success rates and
complicated gating techniques15,16
. The recent advent
of the automated spatio-temporal image correlation
(STIC
TM
) technique provided the first 3D and 4D
gray-scale images from the fetal heart17,18
. Recently,
color Doppler and power Doppler have been combined
with gray-scale STIC technology, making possible the
assessment of hemodynamic changes throughout the
cardiac cycle and in the different cardiac cavities. The
purpose of this study was to evaluate the clinical potential
of color Doppler STIC in normal fetuses and in those
with heart malformations, aiming firstly to obtain offline
the three defined planes from stored 4D volumes, and
secondly to demonstrate new spatial views of the fetal
heart in 3D/4D volume rendering.
METHODS
Basics of the spatio-temporal image correlation (STIC)
technique, volume acquisition and display
A short summary of the STIC principle is presented here;
a more detailed description is given in a previous study by
DeVore et al.17
. The integrated STIC software permits the
acquisition of a cardiac volume dataset by analyzing and
correlating numerous images from different heart cycles
obtained during an automated sweep. The duration of the
acquisition can be adjusted by the examiner (7.5, 10, 12.5
or 15 s). The acquisition angle sweep ranges from 15◦ to
40◦
. The rendered volume includes a single ‘hypothetical’
cardiac cycle, which is reconstructed from selected images
of the acquisition plane (A-plane) during different phases
of the heart cycle. The quality of the heart volume dataset
depends on the frame rate of the two-dimensional (2D)
image, the angle sweep and the acquisition time. The
more images stored per acquisition period, the greater
the number available for the reconstruction of a volume
and the better the resolution. Color and power Doppler
have a slower frame rate compared with gray scale during
scanning, which leads unavoidably to a reduction in image
quality using color STIC when compared with gray-
scale STIC. Once the volume is successfully obtained,
it is displayed on the screen in a multiplanar image
format, demonstrating one cardiac cycle beating in the
three orthogonal planes (Figures 1 and 2). The A-plane
is the acquisition plane and has the best image quality
(upper left). The B (upper right) and C (lower left) planes
are the orthogonal planes which have been reconstructed
by the system. Therefore, the quality of the acquired
volume can be estimated online by directly analyzing
the B-plane. The examiner can repeat the acquisition if
necessary, for example if fetal movements occurred during
acquisition. The sweep angle can be widened if this was
too narrow, and the mother can be asked to suspend
breathing if maternal movements were recognized. The
heart volume dataset can also be displayed as a single
image of a 3D/4D surface or a transparent volume, in
which gray-scale or color Doppler information or both can
A-PLANE B-PLANE
C-PLANE
LV
RV
RA
LA
Figure 1 Color Doppler spatio-temporal image correlation volume of a 26-week fetus displayed in the multiplanar mode. The A-plane is the
acquisition plane, the B-plane is the orthogonal plane vertical to the A-plane and the C-plane is the orthogonal plane horizontal to the
A-plane. The arrow shows the cineloop bar, which when activated allows visualization of heart contractions and color Doppler changes in
the different planes (cf. Figure 3). In the right lower corner an orientation box can be displayed, demonstrating in this case that the A-plane
is activated. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
Copyright  2004 ISUOG. Published by John Wiley & Sons, Ltd. Ultrasound Obstet Gynecol 2004; 23: 535–545.

Color Doppler STIC 537
LV
RV
LV
RV
Figure 2 One application of the multiplanar mode is demonstrated in this fetus with a ventricular septal defect (VSD) showing shunting
from the left to the right ventricle (blue color crossing the septum). The arrows point to the dot present in all three planes which shows the
intersection point of these planes. The examiner can place the dot in the region of interest in one plane (here in the A-plane) and see its
position in both the other planes. In this case the dot has been placed on the VSD in plane A, which is then pinpointed in planes B and C.
LV, left ventricle; RV, right ventricle.
LV RV
RA
LA
LV
AO
RV
AO
TP
SVC
Trachea
DA
ISTH
a b c
Figure 3 One of the possible displays of the multiplanar view is offline re-examination. Taking the volume of Figure 1, the A-plane has been
magnified and visualized alone. By scrolling through the volume the examiner can visualize ‘any plane’. Three planes are presented: the
four-chamber view (a), the five-chamber view (b) and the three vessels and trachea view (c). By using the cineloop the examiner can choose
within the volume the heart cycle phase of interest. Compare also with Figures 6 and 7. AO, aorta; DA, ductus arteriosus; ISTH, aortic
isthmus; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle; SVC, superior vena cava; TP, pulmonary trunk.

538 Chaoui et al.
be demonstrated (so called ‘glass body’ mode), providing
spatial relationships as for gray-scale STIC17.
Study population
The study population included 62 fetuses, consisting
of 35 fetuses with normal anatomy and 27 with a
structural congenital heart defect (CHD). The normal
population was recruited from pregnant women referred
either for routine antenatal sonography or for targeted
cardiac examination due to a positive family history
of heart anomalies. All were singleton pregnancies
between 20 weeks and term with structurally normal
fetuses of appropriate size for gestational age, showing
neither fetal arrhythmia nor other cardiac or extracardiac
abnormalities. Patients gave oral consent to participate
in the study, which was performed during a routine
fetal echocardiography examination. The hospital ethics
committee gave approval to perform the study and to
store volumes for offline evaluation.
The 27 fetuses with CHD were either detected in
our unit or referred for a second opinion ultrasound
examination because of a suspected CHD. They are
grouped according to type of CHD in Table 1 and covered
a range of gestational ages. Following traditional freehand
2D B-mode, color and pulsed Doppler examination of
each fetus, STIC evaluation was performed. No clinical
decisions were made as a result of the 3D findings. We
divided the fetuses with CHD into three groups according
to whether the abnormality was observed with color
Doppler primarily in the four-chamber plane, in the planes
of the great vessels, or in all planes. In addition, we
evaluated the possibility of 3D/4D spatial surface volume
rendering in selected fetuses with CHD.
Examination technique
Ultrasound examinations were performed using a Voluson
730 Expert system (GE Medical systems, Kretztechnik,
Zipf, Austria) and the transabdominal probe (RAB-
4–8MHz) was used to acquire the STIC volumes. STIC
software can be used either for gray-scale imaging17–19
or in combination with color and power Doppler. Our
learning curve with color STIC was rapid due to previous
experience with gray-scale STIC20.
Comprehensive 2D and color Doppler fetal echocar-
diography was performed with the 3D transducer. On
completion of the examination a manual sweep was per-
formed to determine whether all structures of interest
were included in the acquired volume and the 3D STIC
acquisition was activated. Volume datasets were acquired
when fetuses were in a dorsoposterior position allowing
either apical, right-sided or left-sided insonation of the
heart. The manufacturer’s settings for cardiac evaluation
were used and slightly modified according to individual
conditions, keeping the image frame rate as high as pos-
sible. The color box size was therefore selected to be as
narrow as was needed for image acquisition. For the pur-
poses of this study only transverse cardiac sweeps were
Table 1 Details of fetuses with congenital heart defects (CHD) and
the gestational age at examination divided according to whether the
abnormality can be demonstrated by color Doppler in the
four-chamber plane, in the five-chamber or three vessels and
trachea view, or in all three planes
Diagnosis Gestational age (weeks)
Anomalies of the chambers
VSD 33
VSD 22
VSD 24
AVSD 33
AVSD 23
Rhabdomyoma 22
Anomalies of the great vessels
TOF 30
TOF, PA 29
TOF, APVS 24
D-TGA 26
D-TGA 28
CoA 30
D-AoA 28
R-AoA 26
DORV 35
PS/PI 32
TAC 22
Combined anomalies
HLHS 22
HLHS 20
HLHS 25
PA-IVS, TI 23
PA-IVS, severe TI 31
PA-IVS, VCAC 21
Ebstein, PA 27
SV-DORV, R-AoA 22
SV-DORV, R-iso 18
D-TGA + VSD 32
APVS, absent pulmonary valve syndrome; AVSD, atrioventricular
septal defect; CoA, aortic coarctation; D-AoA, double aortic arch;
DORV, double outlet right ventricle; D-TGA, d-transposition of
great arteries; HLHS, hypoplastic left heart syndrome; PA,
pulmonary atresia; PA-IVS, pulmonary atresia with intact
ventricular septum; PS/PI, pulmonary stenosis and insufficiency;
R-AoA, right aortic arch; R-iso, right isomerism; SV, single
ventricle; TAC, truncus arteriosus communis; TI, tricuspid
insufficiency; TOF, tetralogy of Fallot; VCAC,
ventriculocoronary–arterial communications; VSD, ventricular
septal defect.
obtained to keep the examination as similar as possible to
the proposed transverse 2D gray-scale and color Doppler
planes3,6
. The acquisition angle of the volume box was
selected between 15◦ and 35◦ according to the depth of
the fetus in utero and to the size of the heart. Acquisition
time ranged between 7.5 and 15 s, with 10-s acquisition
times being most commonly used. In all cases with color
STIC we attempted to maintain the image frame rate
higher than 17 Hz to allow acquisition of a high num-
ber of images. Mechanical and thermal indices in color
Doppler were kept as low as possible according to the
ALARA principle21
. After an adequate volume acquisi-
tion had been obtained, the volume data were stored on
the hard disk of the computer. One to three STIC color

LV
RV
RA
LA
RV
TI
Figure 4 Spatio-temporal image correlation color volume of a fetus with hypoplastic right ventricle (pulmonary atresia with intact septum).
The A-plane is magnified showing the four-chamber plane. By scrolling through the cineloop the only filling of the left ventricle during
diastole can be demonstrated (a) as can the tricuspid insufficiency (TI) during systole (b). LA, left atrium; LV, left ventricle; RA, right atrium;
RV, right ventricle.
volumes were stored for each examination. The examina-
tions were exported to a compact disk and transferred to
a personal computer (PC) for later offline evaluation using
specialized 3D software (4D View, GE Medical systems).
Two examiners experienced in fetal echocardiography
reviewed the color Doppler STIC volumes.
RESULTS
3D and 4D volume acquisitions were technically possible
in all cases. Since the examiner observes online the success
of the acquisition, a second attempt can be made if
necessary. The most common reason for performing a
second volume acquisition was mainly a small sweep
acquisition angle that did not include the great vessels; this
occurred in 9/35 fetuses. We did not try to acquire volumes
only with a strict apical view, since this does not reflect real
examination conditions. In the multiplanar mode we were
able to obtain in most fetuses, both those with normal and
those with abnormal hearts, the necessary information
in the corresponding planes. Figure 1 illustrates the
multiplanar mode showing A, B and C-planes. Figure 2
demonstrates how the reference dot can be placed in one
region of interest, simultaneously pinpointing this area in
the two orthogonal planes. Figure 3 illustrates the three
planes of interest in their corresponding phase during
the heart cycle. Figure 4 demonstrates a hypoplastic
right ventricle in which one plane (A-plane) is displayed
during both systole and diastole (tricuspid regurgitation).
Figures 5 and 6 show how from a stored volume the
three planes with their typical color Doppler findings
can be reviewed offline. This potential of the technique
is demonstrated for two heart anomalies, hypoplastic
left heart syndrome (Figure 5) and tetralogy of Fallot
(Figure 6).
In the group of normal fetuses 4/35 (11.5%) had an
incomplete examination using color Doppler STIC, due
mainly to perpendicular insonation in one of the three
planes of interest. In one fetus the aorta did not show
perfusion in a perpendicular right-sided heart insonation
(Figure 7). In two other cases visualized from the left
side the three vessels and trachea (3VT) view was seen
on a real-time image but no flow was observed in the
horizontal vessels. In the fourth case the four-chamber

540 Chaoui et al.
RV
RALA
LV
AAO
LV
Aortic
Isthm
TP
Trachea
Figure 5 Spatio-temporal image correlation color volume of a 20-week fetus with hypoplastic left heart syndrome. Scrolling through the
planes of the volume allows demonstration of the findings in the three planes (cf. Figure 3). The four-chamber view (a) shows the filling of
the right ventricle during diastole and the empty hypoplastic left ventricle. The five-chamber view (b) shows the atretic hypoplastic aortic
root with no antegrade flow in the ascending aorta (AAO). The three vessels and trachea view (c) shows the antegrade flow (blue) through
the slightly dilated pulmonary trunk and the retrograde flow (red) in the hypoplastic aortic isthmus. Isthm, isthmus; LA, left atrium; LV, left
ventricle; RA, right atrium; RV, right ventricle; TP, pulmonary trunk.
view was insonated perpendicularly from the right side
and did not show optimal filling of the chambers.
In the 27 fetuses with heart abnormalities, inappro-
priate volumes were obtained in three cases (11%), one
with a double outlet right ventricle seen at 35 weeks, in
which rib shadows and a narrow volume sweep hindered
visualization of the origin of one of the two vessels from
the right ventricle. In another case with coarctation of the
aorta at 36 weeks the continuity and perfusion of the aor-
tic arch could not be observed in the acquired volume due
to the fixed fetal position and rib shadowing. In the third
fetus at 18 weeks a right isomerism and double outlet
ventricle with anterior–posterior transposed vessels was
diagnosed. In the transverse plane only one vessel could
be seen and in the reconstructed longitudinal plane the
resolution was not sufficient to permit a reliable demon-
stration of the finding. A longitudinal acquisition was not
achieved since this was not part of the study protocol.
Volume rendering was attempted in several cases to
obtain experience with this new technology. In eight
selected cases we rendered the spatial 3D/4D volumes
by demonstrating a cranial view of the heart and
vessels in a glass body display (Figures 8 and 9). Figure 8
illustrates how within the volume the examiner can see
simultaneously the chambers and the criss-crossing of
the great vessels, while Figure 9 shows two examples of
abnormalities: a transposition of the great arteries and a
double aortic arch. In six cases the atrioventricular valves
and the great vessels were visualized in an ‘en-face’ view14
(Figures 10 and 11) and in an additional four cases the
interventricular septum was rendered, viewed from the
right or left ventricle.
DISCUSSION
Spatio-temporal image correlation (STIC) feasibility
and comparison with previous studies
This study demonstrates the feasibility of using STIC
technology in combination with color Doppler to provide
3D/4D imaging of fetal cardiac flow in normal fetuses and
in fetuses with CHD. Previous systems used volume data
acquisitions based either on a static volume sweep12,22,23
or on attempts to gate the heart rate signal by means
of spectral Doppler15
or cardiotocography16
. Recent
reports on gray-scale STIC demonstrated clearly the
ease of use and the advantages of this new technique
in providing 3D/4D information on the fetal heart in
the second half of gestation17–20. Deng24 suggested in
an Opinion in this Journal that terminology should
be used to describe accurately the system used when
reporting 3D and 4D image acquisitions of the fetal
heart. We believe that STIC could be defined as an
‘online’ system with an ‘indirect volume scan’ and ‘post-
3D/4D-acquisition correlation’. The color Doppler STIC

LV RV
RALA
LV
AO
RV
AO
TP
SVC
DA
RV
Figure 6 Spatio-temporal image correlation (STIC) color volume of a 24-week fetus with tetralogy of Fallot. By scrolling through the STIC
volume all three planes can be demonstrated (cf. Figure 3). The four-chamber plane (a) appears normal during diastole. The five-chamber
plane (b) shows the overriding of the aorta receiving blood from both ventricles (arrows). The pulmonary trunk appears smaller than the
aorta with antegrade flow (c). AO, aorta; DA, ductus arteriosus; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle;
SVC, superior vena cava; TP, pulmonary trunk.
LV
AO
RV
Figure 7 Limitation of color Doppler spatio-temporal image
correlation (STIC) related to insonation angle. This STIC color
volume was acquired from a right-sided four-chamber view and the
aorta is lying horizontally. Due to the perpendicular insonation of
the aortic valve, blood flow is not appropriately visualized (arrow).
AO, aorta; LV, left ventricle; RV, right ventricle.
approach is the first system to allow rapid, online
image acquisition and display of information of spatial
intracardiac flow. There are only a few reports of 3D/4D
rendering of fetal cardiac blood flow. Experience with
non-gated 3D static power Doppler has been reported by
our group12,22,23,25
, which found it to have limitations
as a result of the contracting heart hindering reliable
rendering of the volume. In the last 2 years two studies
have reported gated 3D/4D fetal echocardiography in
combination with color Doppler15,16
. In the study by
Deng et al.15
two transducers were utilized, one for
image acquisition and one for heart rate assessment by
spectral Doppler. They were successful in triggering 8/15
attempts performed, obtaining six volumes with useful
information, and complete information being obtained
in only four cases. A similar observation was reported
by Herberg et al.16
. According to our experience, STIC
technology combined with color Doppler solved most of
the problems confronted by other authors. If the examiner
has experience with color Doppler settings on the 2D
image, the learning curve will be very short. The main
advantages of the system are the use of a single probe for
the 2D and 3D examinations, with integrated software,
and the short acquisition and display time, which occurs
within 30 s instead of the 15–30 min reported in the
other studies15,16
. This may promote this system as a
new tool that can be introduced into routine fetal cardiac
screening, with its main advantage being the possibility of
storing volumes of one cardiac cycle with color Doppler
information. Our study showed that the multiplanar

542 Chaoui et al.
LV RV
RALA
LV
A AO
RV
TP
A Arch
TP
DA
AO
Figure 8 4D volume rendering with transparent gray-scale and surface color Doppler. The examiner looks at the heart volume from a
cranial approach visualizing the great vessels and the chambers beneath (or behind in the image). By scrolling through the cineloop the
different phases of the cardiac cycle can be visualized as the diastolic filling of the ventricles (a), the beginning of systole with blood flow
streaming in the outflow tracts (b), and late systole with blood still recognizable in both great vessels. In this view the criss-crossing of the
great vessels can be appreciated in a way not seen before in prenatal diagnosis (cf. transposition in Figure 9b). Due to the presetting of color
persistence the volume in (b) shows simultaneously late diastole (red filling of chambers) and early systole (filling of the vessels). AAO,
ascending aorta; A Arch, aortic arch; AO, aorta; DA, ductus arteriosus; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right
ventricle; TP, pulmonary trunk.
TPAO TP
AO
TP AO
Trachea
R
L
DA
Figure 9 The same view as demonstrated in Figure 8. (a) A normal finding with the regular criss-crossing of the aorta (AO) and pulmonary
trunk (TP). (b) A fetus with transposition of the great arteries with parallel course of both vessels; the two ventricles in late diastole can be
seen (cf. Figure 8b). (c) A fetus with a double aortic arch; the three-dimensional rendering demonstrates the bifurcation (arrows) of the aortic
arch in front of the trachea (line) into left (L) and right (R) arches. The ductus arteriosus (DA) connects to the left aortic arch.
display in most (90%) cases (with either a normal or
abnormal heart) permits a reliable offline demonstration
of the findings, considering also hemodynamic changes
that occurred during the cardiac cycle (Figures 1–6). In
our opinion the information and data content in such a
volume are far greater than can be obtained from a series
of still images or video clips stored on a digital archiving
system. Color Doppler STIC is the only tool available
which permits the examiner to reliably recreate the color
Doppler examination of the fetal heart offline and review
the examination at a later time.
Multiplanar mode display
The three color Doppler planes we proposed recently6
namely the four-chamber, the five-chamber- and the 3VT

TV
MV
TP
AO
RALA
Figure 10 4D surface rendering of the atrioventricular (AV) and semilunar valves during diastole–systole in the en-face view of the AV
valves. The view as shown by the green bar (a) is from the heart base towards the apex. In the rendered image (b) the en-face view of both
mitral (MV) and tricuspid valve (TV) is demonstrated during diastolic flow (red) (cf. Figure 11b). Due to increased persistence of color
Doppler, blood flow in early systole is seen simultaneously. Therefore the embedded aorta (AO) can be recognized between both AV valves,
and the pulmonary trunk (TP) is in a normal position anterior to the aortic valve (cf. Figure 11b). LA, left atrium; RA, right atrium.
Common AV-valve
TVMV
TP AOTP
AO
Figure 11 En-face view in two fetuses with a heart anomaly (cf. normal fetus in Figure 10). (a) A fetus with atrioventricular septal defect
showing the common valve demonstrated by a single wide flow. (b) A fetus with complete transposition of the great arteries with
side-by-side vessels, the aorta (AO) being anterior and on the right side (d-transposition) of the pulmonary artery (TP). MV, mitral valve;
TV, tricuspid valve.

544 Chaoui et al.
views, can be reliably evaluated using color Doppler STIC
volume datasets, with a 90% success rate. This approach
was successful in 24/27 fetuses with cardiac anomalies
and allowed a reviewer at a remote site to visualize the
abnormality using at least one of the three planes. The
advantages of such a volume dataset is that it can be
displayed as a 2D cardiac cycle in a cineloop (Figure 4)17
.
The loop may be demonstrated in slow motion or stopped
at any time to be analyzed frame-by-frame, as shown in
Figure 4 for diastole and systole. The visualization of
color Doppler information can also be changed gradually
by manually changing the ‘color threshold’ button. Each
of the scan planes can be moved and rotated during the
synchronized cardiac loop and displayed as a single image
(Figures 3–5) or as a combination of three orthogonal
planes (Figures 1 and 2)17. A reference dot that can be
placed anywhere on the image by the examiner can
assist in the visualization of the spatial orientation of
the three orthogonal planes, as shown in Figure 2 for
a ventricular septal defect demonstrated in the A-, B-
and C-planes. This dot is used to facilitate orientation
within the STIC volume17,19
. Such a STIC volume dataset
can not only be used for a second opinion by a fetal
cardiology expert17
but it could also be used for teaching
fetal echocardiography.
Limitations of the technique
The system we used also has some limitations and
may produce artifacts as reported elsewhere17
. Besides
artifacts typical for 3D volume acquisition such as fetal
or maternal movements, there are limitations typical of
STIC technology which occur with arrhythmias. Because
of this fetuses with ectopic beats were excluded from
the study as in other studies with heart rate gating.
Other artifacts such as a non-magnified heart, a short
acquisition time and a wide sweep angle were avoided
by optimizing the image before activating the volume
acquisition. Limitations specifically related to color STIC
were the missing color Doppler signals when the vessel
was perpendicular to the ultrasound beam (Figure 7).
Because of the orientation of the heart, this artifact
may be difficult to avoid in at least one of the three
displayed orthogonal views. To avoid this problem the
examiner should angle the transducer to obtain a cardiac
plane with blood flow visualized in the structures of
interest. Another method that can be used to address
this problem is to acquire several volumes from different
angles, which are then likely to include the information
of interest. This aspect should be considered in future
studies when volumes are sent via the Internet to obtain
a second opinion from an expert in fetal cardiology. This
disadvantage is inherent to color Doppler and is not found
in gray-scale STIC, with which image acquisition can be
achieved from any angle.
Potential of spatial 3D/4D volume rendering
This study focused mainly on the feasibility of acquiring a
heart volume and on the reliability of multiplanar display
of images in comparison with the standard color Doppler
planes. An additional benefit of this new technique
is 3D/4D surface and transparent volume rendering
(Figures 9 and 10), allowing a spatial impression of the
heart and great vessels. The 3D/4D rendering is obtained
offline using the workstation by simply choosing the
function ‘rendering’. The examiner should then place
the render view direction bar (green line, Figure 10) so
as to obtain a view of the volume of interest. In this
study we tried rendering from three different views: from
a cranial approach, from a basal approach looking en-
face to the atrioventricular (AV) valves and the great
vessels, and from a septal approach looking at the
interventricular septum from either the left or the right
side. This preliminary experience shows that such 3D/4D
rendering can be helpful in visualizing the relationship of
the great vessels to each other (Figures 9–11), perfusion
across the AV valves (Figures 10 and 11) and through a
ventricular septal defect. Further studies are necessary to
examine this new approach to fetal heart diagnosis.
CONCLUSIONS
In summary, we have shown in this study that the
combination of STIC with color Doppler provides
the examiner with a volume dataset that combines
information regarding structure, blood flow dynamics
and intracardiac flow. After adjusting the color Doppler
presets the technique is easy to use and provides
reliable volume datasets. These can be displayed in a
multiplanar format permitting offline re-examination. We
have demonstrated that planes proposed and used in color
Doppler echocardiography can be obtained offline from
a volume dataset using an external workstation. There is
an additional possibility of using this technology to view
3D/4D surface and transparent volume rendered views, a
new method with which to examine the fetal heart in a
spatial dimension that requires further study.
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