Eur Radiol
DOI 10.1007/s00330-010-1822-7 PEDIATRIC
Zhaoping Cheng
Ximing Wang
Yanhua Duan
Lebin Wu
Dawei Wu
Baoting Chao
Cheng Liu
Zhuodong Xu
Hongxin Li
Fei Liang
Jian Xu
Jiuhong Chen
Received: 28 December 2009
Revised: 15 March 2010
Accepted: 12 April 2010
# European Society of Radiology 2010
Low-dose prospective ECG-triggering
dual-source CT angiography in infants
and children with complex congenital heart
disease: first experience
Abstract Objective: To explore the
clinical value of low-dose prospec-
tive ECG-triggering dual-source CT
(DSCT) angiography in infants and
children with complex congenital
heart disease (CHD) compared with
transthoracic echocardiography
(TTE). Methods: Thirty-five patients
(mean age: 16months, range: 2months
to 6years; male 15; mean weight:
12kg) underwent low-dose prospec-
tive ECG-triggering DSCT angiogra-
phy and TTE. Surgeries were
performed in 29 patients, and con-
ventional cardiac angiography (CCA)
was performed in 8 patients. The
accuracy was calculated based on the
surgical and/or CCA findings. The
overall imaging quality was evaluated
on a five-point scale. Results: A total
of 146 separate cardiovascular
deformities were confirmed. DSCT
missed three atrial septal defects
and a patent ductus arteriosus. The
accuracy of DSCT angiography and
TTE was 97.3% (142/146) and
92.5% (135/146), respectively.
Overall test parameters for DSCT
angiography and TTE were similar
(sensitivity, 97.3% vs 92.5%;
specificity, 99.8% vs 99.8%). The
average subjective image quality
score was 4.3±0.7. The mean
effective dose was 0.38±0.09mSv.
Conclusions: Prospective ECG-
triggering DSCT angiography with a
very low effective radiation dose
allows the accurate diagnosis of
anomalies in infants and children with
complex CHD compared with TTE.
It has great promise to become a
commonly used second-line
technique for complex CHD.
Keywords Congenital heart disease .
Prospective ECG-triggering .
Dual-source CTangiography .
Transthoracic echocardiography .
Radiation exposure
Introduction
Conventional cardiac angiography (CCA) is the recognised
gold standard method for assessment of complex congen-
ital heart disease (CHD) in infants and children, but it is an
invasive procedure with a potential procedure-related
mortality of around 1% [1] and has the potential to impart
high radiation doses [2]. Because of the risk, several non-
invasive examination methods have been proposed as the
major techniques for investigating complex CHD in
children with the aim of decreasing the use of CCA.
Although transthoracic echocardiography (TTE) is usually
the initial choice because of the availability and the logistic
simplicity, it may not be the perfect diagnostic tool because
it is limited by the acoustic window, spatial resolution and
the subjective interpretation of the operator [3].
Recently, multi-detector CT with improved spatial and
temporal resolution has been used more frequently in
children with CHD [4–8]. Non-ECG-gated imaging is
usually used for the evaluation of extracardiac structural
abnormalities [5, 9]. Retrospectively ECG-gated CT was
performed when morphological evaluation of rapidly
moving intracardiac or paracardiac structures, including
the ascending aorta, cardiac valves and coronary artery,
Z. Cheng :X. Wang ()) :Y. Duan :
L. Wu :D. Wu :B. Chao :C. Liu : Z. Xu
Shandong Medical Imaging Research
Institute,
Shandong University,
No.324, Jingwu Road, Jinan, Shandong
250021, China
e-mail: wxming369@163.com
Tel.: +86-531-86760780
Fax: +86-531-85186707
H. Li : F. Liang
Department of Cardiovascular Surgery,
Shandong Provincial Hospital, Jinan,
Shandong, China
J. Xu : J. Chen
CT Research Collaboration,
Siemens. Ltd. China, Beijing, China
was required [6, 10]. However, the use of a low pitch or
overlapping spiral CT acquisition results in the relatively
high radiation dose of a retrospective ECG-gated exami-
nation [7, 8]. Although the combined use of dose-saving
methods including a body-size-adaptive CT protocol, low
tube voltage and tube current modulation [11, 12] can
reduce the CT dose to 3–6 mSv for the patients with CHD
[13], high radiation is still the major inherent limitation for
retrospective ECG-gated CT.
Recently, prospective ECG-triggering or the step-and-
shoot (SAS) technique, has been proposed to decrease
radiation exposure in cardiac CT [14]. With this
technique, radiation is only administered at predefined
time points of the cardiac cycle, which is likely to be
associated with a substantial reduction of the radiation
dose. Recent studies have found that low-dose prospec-
tive ECG-triggering CT angiography is feasible in adults
with mean heart rates below 70 bpm with a low effective
dose of 1–4 mSv [15, 16]. The upper mean heart rates
were not evaluated in terms of the feasibility of
prospective ECG-triggering CT. With the combination
of 83-ms temporal resolution of dual-source CT (DSCT),
potential application in patients with higher heart rates
has become possible [17].
To our knowledge, so far there have been no studies
demonstrating the feasibility of prospective ECG-trigger-
ing DSCT angiography in infants and children. The
purpose of this study is to explore the clinical value of
low-dose prospective ECG-triggering DSCT angiography
in infants and children with complex CHD.
Materials and methods
Patients
Our study was approved by the local ethics board; written
informed consent was obtained from all patients (their
parents). In our institute, CT angiography is part of the
cardiovascular evaluation in patients with complex CHD
according to the clinical indications. As no precise
definition exists, “complex” CHD is defined as congenital
heart disease with more than one separate cardiovascular
anomaly by their transthoracic echocardiography findings
in this study.
We prospectively enrolled 45 patients with complex
CHD between January and May 2009 in our institute.
General exclusion criteria for contrast-enhanced CT included
nephropathy (serum creatinine level >150 mmol/l) (n=1)
and known hypersensitivity to iodine-containing contrast
medium (n=1). Patients with non-sinus rhythm were
excluded from the study (n=1). Patients who had undergone
palliative or corrective surgeries were also excluded (n=7).
A total of thirty-five patients (mean age: 16 months,
range: 2 months to 6 years; male 15; mean weight: 12 kg;
mean heart rate: 115 bmp, range: 90–142 bmp) with
complex CHD could be included in this study. All patients
underwent low-dose prospective ECG-triggering DSCT
angiography and TTE. Palliative or corrective surgeries
were performed in 29 patients, and CCAs were performed
in 8 patients. Prospective ECG-triggering DSCT angiog-
raphy was performed without complications in all patients.
There was no extravasation of contrast material at the
injection site. There was no systemic reaction to the
contrast material.
Prospective dual-source CT protocol
All prospective ECG-triggering DSCT angiography
examinations were performed using a DSCT (Somatom
Definition, Siemens, Forchheim, Germany) during free-
breathing. Sedation was achieved with peroral chloral
hydrate and administered according to the patient’s body
weight and clinical condition. The anatomical region
covered by the CT data acquisition was from the thoracic
inlet level to L1–2.
The following acquisition parameters were used: 2×
32×0.6 mm detector collimation, a slice collimation of 2×
64×0.6 mm enabled by Z-Sharp technology and a gantry
rotation time of 0.33 s. Body weight-based adjustments
of tube voltage and tube current were performed: <5 kg,
tube voltage 80 kV, tube current 40–59 mAs; 5–10 kg,
tube voltage 80 kV, tube current 60–79 mAs; >10 kg, tube
voltage 80 kV, tube current 80–120 mAs. Prospective
ECG-triggering technology necessitated a cycle time of
1.25 s for one acquisition and the subsequent table feed.
The data acquisition window was 380 ms with padding
technique. The centre of the data acquisition window was
set at 40% of the R-R interval. The duration of the CT
data acquisition was 5.39–9.14 s.
A dual-head power injector (Stellant; Medrad, Indianola,
PA) was used. The saline flush technique was applied for all
injections to reduce artefacts caused by undiluted intra-
vascular contrast agent. The high concentration contrast
material (Schering Ultravist, Iopromide, 350 mg I/ml,
Berlin, Germany) was injected via peripheral veins in
the elbow or back of the hand. We used 2 ml/kg of
contrast medium plus the saline flush with half volume
of the total contrast medium. The delay time was set to
25 s. The contrast volume was divided by 30 (the
delay time + 5 s) to produce the flow rate for both
contrast medium and saline chaser. For example, a 5-kg
baby with peripheral access would be injected with
10 ml of iopromide 350 and 5 ml saline flush at 0.5 ml/s
[(10+5)/30].
Image post-processing and analysis
Dual-source CT images were reconstructed in a mono-
segment mode by using a section thickness of 0.75 mm
and a medium smooth-tissue convolution kernel (B26f).
Images were reconstructed from 32% to 48% of the R-R
interval in 2% increments, and the best reconstruction
phase was used for evaluations. All images were trans-
ferred to an external workstation (Multi Modality Work-
place, Siemens, Forchheim, Germany ) for further
analysis. In addition to the CT axial slices, multiple
planar reformation (MPR), volume rendering (VR) and
maximum intensity projection (MIP) were used to
visualise cardiac abnormalities.
The interpretation of prospective ECG-triggering DSCT
angiography was performed without knowing the result of
surgical, CCA or TTE findings. Two radiologists with
more than 5 years’ experience in cardiac radiology semi-
quantitatively assessed the overall image quality inde-
pendently on a five-point scoring system [18] as follows:
5: excellent anatomical clarity; excellent image
quality.
4: good anatomical clarity; all structures are clearly
interpretable.
3: fair anatomical clarity; the anatomical relationships
required clinically could be defined with confidence.
2: poor image quality or anatomical detail; incomplete
demonstration of anatomical structures.
1: no useful information obtained.
For any disagreement in data analysis between the two
observers, consensus agreement was achieved. Examina-
tions graded 3, 4 or 5 were considered sufficient for
complete diagnosis.
Transthoracic echocardiography
Two-dimensional TTE with Doppler ultrasound was per-
formed from the apical, parasternal, subxiphoid and supra-
sternal approaches using a SONOS 7500 ultrasound system
(Philips Medical Systems, Bothell, WA). All studies were
performed by an echocardographic technician with more
than 7 years’ experience and were saved digitally. All
echocardiographic studies were analysed by a paediatric
cardiologist with more than 10 years’ experience blinded to
other studies’ results.
Radiation dose estimations
The parameters for imaging range, dose-length product and
volume CT dose index were obtained from the protocol that
summarised the relevant individual radiation exposure
parameters of each CT angiography examination [19]. The
effective dose delivered at CT cardiac angiography was
derived from the dose-length product and conversion coef-
Fig. 1 A 16-month-old boy
with the diagnosis of
pulmonary atresia with the
fistula between the proximal
RCA and MPA. Prospective
ECG-triggering DSCT was
performed at 80 kV and 80
mAs (effective dose, 0.43
mSv). (a) Multiplanar
reformatted image and (b)
volume-rendered image
(anterior view) show the
fistula (thick arrow) between
the proximal RCA and MPA.
(c) Thick-section oblique
sagittal MIP image shows the
ventricular septal defect
(VSD) and overriding aorta.
(d) Volume-rendered image
(posterior view) shows two
MAPCAs (slim arrows)
arising from the DA. AA =
ascending aorta, RCA = right
coronary artery, MPA = main
pulmonary artery, RPA = right
pulmonary artery, RV = right
ventricle, LV = left ventricle,
MAPCA = main
aortopulmonary collateral
artery, DA = descending aorta
ficients [20]. Infant-specific dose-length product conversion
coefficients were given for a 16-cm phantom: a coefficient of
0.039 mSv/[mGy·cm] until 4 months of age, 0.026 mSv/
[mGy·cm] between 4 months and 1 year of age, and
0.018 mSv/[mGy·cm] between 1 year and 6 years of age [21].
Statistics
The results of surgical or CCA findings were utilised as the
reference standard. Test parameters (sensitivity, specificity,
positive and negative predictive values) were calculated for
separate cardiovascular anomalies, and the 95% CIs were
calculated. Quantitative data were expressed as means ±
standard deviations, and categorical data were given in
proportions and percentages. Interobserver agreement in
subjective image quality grading was assessed by using
kappa statistics, and к-values of 0.61–0.80 corresponded to
good agreement. The accuracy of DSCT angiography and
TTE was compared by using the non-parametric chi-squared
test. A p value<0.05 was considered to indicate a significant
difference.
Results
The final diagnoses of the 35 patients were pulmonary artery
atresia with ventricle septal defect (n=5, Fig. 1), tetralogy of
Fallot (n=10, Figs. 2 and 3), double outlet right ventricle (n=
5), interrupted aortic arch (n=2), coarctation of the aorta (n=
3 Fig. 4), anomalous origin of one pulmonary artery (n=1),
total anomalous pulmonary venous return (n=2), anomalous
systemic venous return (n=1) and transposition of great
arteries (n=6) by surgical and/or CCA findings as the
reference standard.
A total of 146 separate cardiovascular deformities were
confirmed by surgical and/or CCA findings. The accuracy
of low-dose prospective ECG-triggering DSCT angiogra-
phy and TTE in diagnosing separate cardiovascular
deformities was 97.3% (142/146) and 92.5% (135/146),
respectively. DSCT was as accurate as TTE in revealing
cardiovascular deformities (χ2=3.48, P<0.05). Details on
separate cardiovascular deformities are given in Table 1.
Out of the total 735 diagnoses made, 17(2.3%) differences
between DSCT angiography and TTE were found. The
overall deformity-based sensitivity, specificity, positive
Fig. 2 An 8-month-old boy
with tetralogy of Fallot.
Prospective ECG-triggering
DSCTwas performed at 80 kV
and 60 mAs (effective dose,
0.29 mSv). (a) Ventricular
septal defect (VSD) and
overriding aorta on the
reformatted images. (b) Thick-
section oblique sagittal MIP
image during systole shows
critical stenosis of the right
ventricular outflow tract
(RVOT). RCA = right
coronary artery, RV = right
ventricle, LV = left ventricle,
Ao = aorta, MPA = main
pulmonary artery, LPA = right
pulmonary artery
Fig. 3 A 1-year-old boy with
tetralogy of Fallot. Prospective
ECG-triggering DSCT was
performed at 80 kV and 70
mAs (effective dose, 0.38
mSv). (a) Thick-section
oblique sagittal MIP image
shows critical stenosis of the
pulmonary valve (white
arrow). (b) Oblique coronal
multiplanar reformatted image
shows patent ductus arteriosus
(PDA) between aortic arch
(Ar) and left pulmonary artery
(LPA). Note stenosis of the
proximal LPA (black arrow).
RV = right ventricle, MPA =
main pulmonary artery, RPA =
right pulmonary artery
predictive value and negative predictive value were
97.3%, 99.8%, 99.3% and 99.3%, respectively, by DSCT
angiography, and 92.5%, 99.8%, 99.3% and 98.2%,
respectively, by TTE (Table 2).
In four patients, TTE missed all of the coronary artery
anomalies. In one patient with tetralogy of Fallot (Fig. 5), the
right coronary artery arose from the left coronary sinus of
Valsalva, which distributed two larger branches crossing in
front of the right ventricular outlet. In another patient with
transposition of the great arteries (Fig. 6), both the right
coronary artery and the left coronary artery arose from the
non-coronary sinus of Valsalva with a common ostium. The
left main coronary crossed between the main pulmonary
artery and the left atrium. In the remaining two patients, one
coronary-pulmonary fistula and one high-take off of the left
coronary artery were missed by TTE. TTEmissed two major
aortopulmonary collateral arteries, three distal pulmonary
artery stenoses and one anomalous systemic venous return.
Fig. 4 A 14-month-old girl with coarctation of the aorta. Prospective
ECG-triggering DSCT was performed at 80 kV and 80 mAs (effective
dose, 0.41 mSv). (a) Multiplanar reformatted image shows
simultaneously the atrial septum defect (ASD) and muscular
ventricular septal defect (VSD) accompanied by coarctation of the
aorta. (b) Volume-rendered image (posterior view) demonstrates
narrowing of the aortic isthmus (arrow). RA = right atrium, LA =
left atrium, RV = right ventricle, LV = left ventricle, AA = ascending
aorta, Ar = aortic arch, DA = descending aorta, LSA = left subclavian
artery, RSA = right subclavian artery
Table 1 Findings at prospective ECG-triggering dual-source CT (DSCT) angiography and transthoracic echocadiography (TTE) in refe-
rence to surgical findings and/or conventional cardiac angiography (CCA; n=35)
Cardiovascular deformities Surgeries and/or CCA DSCT findings TTE findings
TP TN FP FN TP TN FP FN
Atrial septal defect 16 13 18 1 3 16 19 0 0
Ventricular septal defect 28 28 7 0 0 28 7 0 0
Right ventricular outflow tract stenosis 8 8 27 0 0 8 27 0 0
Double outlet right ventricle 5 5 30 0 0 5 30 0 0
Atrioventricular discordance 1 1 34 0 0 1 34 0 0
Pulmonary valve stenosis 3 3 32 0 0 3 32 0 0
Pulmonary artery stenosis 15 15 20 0 0 12 20 0 3
Patent ductus arteriosus 10 9 25 0 1 10 25 0 0
Pulmonary artery atresia 5 5 30 0 0 5 30 0 0
Dilated pulmonary artery 6 6 29 0 0 6 29 0 0
Anomalous origin of pulmonary artery 1 1 34 0 0 1 34 0 0
Anomalous pulmonary venous return 2 2 33 0 0 2 33 0 0
Anomalous systemic venous return 1 1 34 0 0 0 34 0 1
Overriding aorta 16 16 19 0 0 16 19 0 0
Coarctation of the aorta 3 3 32 0 0 3 31 1 0
Interrupted aortic arch 2 2 33 0 0 1 33 0 1
Transposition of the great arteries 6 6 29 0 0 6 29 0 0
Major aortopulmonary collateral artery 5 5 30 0 0 3 30 0 2
Right aortic arch 5 5 30 0 0 5 30 0 0
Double superior vena cava 4 4 31 0 0 4 31 0 0
Coronary artery anomaly 4 4 31 0 0 0 31 0 4
Total 146 142 588 1 4 135 588 1 11
TP, true positive detection; TN, true negative detection; FP, false positive detection; FN, false negative detection
TTE misdiagnosed one patient as having coarctation of the
aorta; operative and DSCT findings confirmed the actual
diagnosis of interrupted aortic arch. On the other hand,
DSCT misdiagnosed one normal atrium as one atrial septal
defect and missed three atrial septal defects and a very small
patent ductus arteriosus. One patient without atrial septal
defect was misdiagnosed because of the streak artefacts
produced by high-attenuation contrast material at the right
atrium. In other patients, very small atrial septal defects
(<3 mm) were missed.
Subjective evaluation of image quality
Interobserver agreement was reached in all patients. The
average subjective overall image quality score of pro-
spective ECG-triggering DSCT was 4.3±0.7 (range 3–5):
score 3 (n=4, 11%), score 4 (n=15, 43%) and score 5 (n=
16, 46%). Diagnostic images (images graded 3 or more)
were obtained in all examinations. There was good
agreement (к=0.78) for overall image quality scoring
between the two reviewers.
Radiation dose estimations
The mean volume CT dose index was 1.39±0.40 mGy
(range: 0.83–1.92). The mean dose-length product was
19.86±6.27 mGy·cm (range: 10–32), resulting in an
estimated mean effective radiation dose of 0.38±0.09 mSv
(range: 0.25–0.58). Radiation dose estimates for each patient
in prospective ECG-triggering DSCT angiography are
shown in Table 3.
Discussion
Our study results indicate the technical and clinical
feasibility of low-dose prospective ECG-triggering DSCT
angiography in infants and children with complex CHD.
The accuracy of prospective ECG-triggering DSCT angiog-
raphy in diagnosing cardiovascular deformities was 97.3%
(142/146). Prospective ECG-triggering DSCT angiograp