PTA is an uncommon congenital cardiac abnormality that occurs due to conotruncal septation failure during fetal development and is correlated with chromosome 22q11 deletion and DiGeorge syndrome . It is always accompanied by VSD and other cardiovascular abnormalities. An early surgical repair is an ideal option in its management. The accurate delineation of morphological characteristics and associated cardiovascular anomalies are essential for the surgical strategies and outcomes. Thus, the exact preoperative diagnosis of these anomalies is imperative.
DSCT, with high temporal and spatial resolution, low radiation, and powerful post-processing techniques, could accurately visualize cardiovascular anomalies. Our study showed 13 patients of typeA1 and only one patient of type A4, which were the most and least common types, respectively. No type B patient was found. These results were entirely consistent with the results confirmed by surgery or CCA. The preoperative measurement of VSD on DSCT was valuable for VSD patch closure must be performed during the operation. The VSDs were always large, for the average diameter in our research was 1.46 ± 0.56cm. Also, the average diameter of TA,MPA༌RPA and LPA can be measured on DSCT. These data could supply detailed quantitative information for the clinicians.
DSCT was superior to TTE in detecting associated cardiac vascular anomalies. It confirmed more accurately than TTE in all extracardiac groups in the present study. The main reasons could be the small field of view examined via suprasternal approach, the pneumatic lung, and the short neck of pediatric patients. Additionally, these structures in the neck and chest were shielded partly by the cervical and thoracic bones, which could also be responsible for the unsatisfactory diagnostic performance for TTE. Our data revealed that DSCT was inferior to TTE for the detection of intracardiac anomalies. The results could be partially attributed to the truth that DSCT is an imaging modality requiring a workstation to transfer digital information to gray-scale images .
Accurate preoperative diagnosis of coronary artery anomalies is critical. Firstly, during the surgical repair of PTA, the right ventricle's infundibulum needs to be incised before restoration of right ventricle-pulmonary artery continuity . Therefore, any malformed coronary artery that goes across the right ventricle's infundibulum could be accidentally damaged during the right ventriculotomy. Secondly, coronary artery anomalies are significant risk factors for death after operation . Our results showed that DSCT could detect this abnormality with 100% sensitivity and 100% specificity. Besides, in the PTA patients, the coronary arteries and pulmonary arteries originate from the truncus artery. It is crucial to identify the ostia number and location of coronary arteries because the coronary ostia or proximal coronary segments could be distorted during the excision of pulmonary arteries from the truncus artery. They could be showed and evaluated accurately by CT, While TTE could miss them .
The concomitant pulmonary artery abnormalities such as crossed pulmonary artery and pulmonary artery stenosis are essential in performing the surgery [6, 14]. In addition, during PTA surgical procedure, detachment of the pulmonary arteries from the arterial trunk was necessary to form a right ventricle to pulmonary artery conduit. So, a noninvasive assessment of the origins and route of pulmonary arteries was crucial. DSCT could provide detailed and comprehensive information about them through powerful post-processing techniques. With regards to aortopulmonary collateral arteries, accurate preoperative evaluation of these collateral arteries could be helpful in surgical planning [5, 25]. DSCT could easily identify the number, origin, branching pattern, and supplied lung lobes. However, only large collateral vessels could be demonstrated on TTE .
The radiation dose is a significant concern undergoing cardiac CT. In our series, several steps were made to reduce radiation dose. Firstly, tube voltage was one of the crucial factors affecting radiation exposure. The tube voltage was set at a low level of 80 kV in our study, which not only decreased the radiation exposure but also made higher cardiovascular enhancement without the loss of contrast-to-noise ratio . Secondly, An ECG-gated sequential technique was used which reduced the radiation dose dramatically. Finally, the heart rhythm adaptive pitch was applied, which adapted higher pitch to fit higher heart rhythm. It reduced both radiation exposure and scanning time. In summary, the estimated mean ED was < 1mSv (0.98 ± 0.37mSv), which was under the ALARA (as low as reasonably achievable) principle.
Our study has several limitations. Firstly, because PTA is rare congenital heart disease, our single-center research had a relatively small number of patients. Further multi-center research is needed for larger sample enrollment. Secondly, radiation exposure is inevitable in CT scanning. Thus, we adopted several effective measures to minimize the radiation dose, and the estimated mean ED was 0.98 ± 0.34mSv, which was under the ALARA principle. Finally, as this is a retrospective study, the selection bias is inevitable.