Fifty patients with double outlet right ventricle referred from radiology department of our institute, in between September 2018 and August 2020 were enrolled. Ethical committee approval of the radiological department of our institute was obtained. Patients diagnosed by echocardiography with double outlet right ventricle in pediatric age group were included in this study. While clinically unstable patients or patients with hypersensitivity to the iodinated contrast and patients with impaired renal function were excluded.
All examinations were performed using a dual source CT scanner (Somatom Definition; Siemens Medical Solutions, Forchheim, Germany). Patient were asked to fast for 2–3 h in neonates and 4–6 h in older children. Venous catheters (21-to 24-gauge) were placed. Description of the procedure to the patients’ parents with their reassurance was performed. Written informed consent (declaring adverse reactions to the iodinated contrast agent and radiation exposure) was obtained from their parents. A crush cart was prepared with a) Adrenaline ampoule if severe hypotension or severe anaphylaxis occurs, B) Anti-histaminic and cortisone to be used if reaction to contrast occurs. Facility for transferring the patient to the intensive care unit if uncontrolled complication develops was planned and available. Short- term sedation was achieved by ketamine with a dose of 1 mg/kg. Non- diluted, non-ionic contrast material was injected (Omnipaque 300–350; Nycomed Amersham, Princeton, NJ) into an antecubital vein at a rate of 1.2–2.5 ml/s, followed by 20 ml of saline solution. The injected volume was adjusted to the body weight (1.5 ml/kg).
Scanning was performed using a Prospective ECG-triggering protocol with the following acquisition parameters: Tube voltage, 80 kV, mAs 60–100 at it was adjusted in each case according to body habitus., Gantry rotation time, 0.28 s; and pitch 3.4
Bolus tracking technique was used with a region of interest (ROI) in the proximal descending aorta or at the left ventricle with a pre-defined threshold between 100 and 150 HU.
Multi-phase examination of the heart was then performed from the inlet of the thorax to 2 cm below the diaphragm level. Sequential series of images in the mid venous and mid arterial phases of enhancement to ensure opacification of both sides of the heart and all extra-cardiac vessels. A scan delay of 4 s was commonly used to evaluate right sided heart structures and a scan delay of 5–8 s is commonly used to evaluate left sided heart structures. Some patients with complex venous anomalies required additional delayed phase after 30–60 s according to patient age, size and heart rate.
Axial images are rapidly reconstructed at 1.0 mm slice thickness and increment of 0.8 mm and reviewed to ensure satisfactory quality of the images.
The patient is kept 15–30 min after the procedure under observation till recovery of sedation.
Image reconstruction of post processing
All acquired data were processed on a workstation (Somatom Definition; Siemens Medical Solutions, Forchheim, Germany). A slice thickness of 0.75 mm and an increment of 0.7 mm were chosen for image reconstruction.
The multiplanar reformation (MPR), maximum intensity projection (MIP), and volume rendering (VR) were used for image analysis.
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Volume rendering (VR)
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VR obtained after editing of axial images to remove bone structures and other soft tissues.
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The VR technique was particularly useful for displaying structures that course parallel or oblique to the transverse plane. It was helpful in the demonstration of the spatial relationship of the extra-cardiac vessels as well as visualization of the pulmonary and systemic venous drainage.
Image analysis
All images were assessed by at least two cardiac radiologists (each having an experience of 7 years at least in cardiac imaging). The patients were retrospectively classified into subgroups according to the relative positions of the great arteries, the relationship between the great arteries and the VSD according to the classification of Society of Thoracic Surgeons database (1), and the presence of associated malformations.
Assessment of the location of the VSD relative to the arterial valves was performed as follows
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If VSD was close to the aortic valve, it was termed a subaortic VSD.
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In a similar manner, if VSD was close to the pulmonary valve, it was termed a sub-pulmonary VSD,
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In a subset of patients, the VSD was remote and associated with AVSD.
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In a few patients, the VSD was committed to both semilunar valves and called doubly committed VSD.
Assessment of the alignment of the great vessels
The alignment of the great vessels was classified as follows:
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If the aorta was posterior and to the right of the main pulmonary artery (MPA), it was termed the right posterior (RP position).
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If two great arteries were side by-side, it was termed the side-by side position.
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If the aorta was anterior and to the right of the MPA, it was termed the right anterior (RA position).
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If the aorta was anterior and to the left of the MPA, it was termed the left anterior (LA position).
Other associated anomalies were also assessed e.g. intra-cardiac anomalies, coronary artery anomalies, anomalies of great vessels, and separate thoracic and abdominal anomalies.
Statistical method
The collected data were coded, tabulated, and statistically analyzed using IBM SPSS statistics (Statistical Package for Social Sciences) software version 18.0, IBM Corp., Chicago, USA, 2009.
Accuracy was represented using the terms sensitivity, specificity, +ve predictive value, −ve predictive value, and overall accuracy.
Accuracy calculations
$$\begin{gathered} {\text{Sensitivity}} = T( + ){\text{ve}} \div\left[ {T( + ){\text{ve}} + F( - ){\text{ve}}} \right] \hfill \\{\text{Specificity}} = T( - ){\text{ve}} \div \left[ {T( -){\text{ve}} + F( + ){\text{ve}}} \right] \hfill \\{\text{Positive\,predictive\,value}} = T( +){\text{ve}} \div \left[ {T( + ){\text{ve}} + F( + ){\text{ve}}}\right] \hfill \\{\text{Negative\,predictive}}\,{\text{value}} = T( -){\text{ve}} \div \left[ {T( - ){\text{ve}} + F( - ){\text{ve}}}\right] \hfill \\ {\text{Overall\,accuracy}} = \left[ {T( +){\text{ve}} + T( - ){\text{ve}}} \right] \div{\text{All\,sample}} \hfill \\ \end{gathered}$$
Estimation of the radiation dose
The scan length was documented for every CT examination. The dose length product (DLP) values were recorded as displayed on the CT console for each CT scan. The effective dose was calculated from the DLP values and using a conversion coefficient of 0.014 for the pediatric chest. The effective dose (msV) of the patient ranged from (0.11 to 0.21) with the mean effective dose was 0.11.
