To date, CT is the largest contributor to medical radiation exposure among the
US and European population[21].This issue is attracting increasing attention, especially in infants and young children, who are more sensitive to radiation. Although higher radiation doses can result in better image quality, but it should be carefully evaluated when used in infants and young children[22–24]. The application of the high-frequency fast scanning technique on the third generation DSCT results in a short radiation time (only 0.25s) and a much lower radiation dose for both groups[25]. Moreover, the attenuation-based TC modulation can reduce radiation dose at approximately 16%ཞ25%[26, 27]. In this study, non-ECG-triggered cardiac CTA has a smaller TC than retro-ECG-triggered cardiac CTA ((54.95 ± 23.52)mAs vs. (45.47 ± 24.65)mAs, p = 0.003), and the ED of both scan protocols were significantly different ((1.48 ± 0.90)mAs vs. (0.35 ± 0.17)mSv, p < 0.001). The minimum effective radiation dose was only 0.1 mSv, which is similar to that noted in Goo et al.’s study[28]. The TC in the non-ECG-triggered group was approximately 17% lower than that in the retro-ECG-triggered group, whereas the effective radiation dose was reduced at approximately 76%. Although retro-ECG-triggered allows a certain period of cardiac cycle (in this study, the data acquisition window setting was 35%ཞ40% of the R-R interval) data collection to obtain high-quality images and reduce the radiation dose, but additional radiation doses generated by overlapping scans were inevitable on this type of data acquisition. Moreover, the scanning field of children with CHD is significantly beyond the range of the heart, which will magnify the incremental radiation power caused by overlapping scanning. Non-ECG-triggered scan can reduce overlapping radiation doses with high pitch and continuous rapid scanning. In addition, we found that the age and weight of the children were similar between groups, and the heart rate did not show considerable difference, however, the TC and DLP were significantly different. We note that in the raw data the radiation dose was reduced when the upper limb was raised. When the upper arm was in a horizontal position, the effect on TC and radiation dose was the greatest, which indirectly verifies the role of automatic TC control technology in radiation dose control[28].
With the rapid sequential cardiac CTA scanning technology, the children`s breathing and heart movement can be frozen, helping to offset the effect of high respiratory motions and cardiac pulsation artifacts on the image quality, thus reducing CT’s dependence on heart rate and breathing[25]. The location of extracardiac structures in the mediastinum is relatively fixed; therefore, images of the extracardiac structures are less affected by respiratory movements than the the intracardiac structures. The image quality scores of both groups on extracardiac structures, such as the aorta, pulmonary artery, and pulmonary vein, were all ≥ 4 points and were not significantly different (all p > 0.05).The scanning window of time was short, although our technicians have remarkable scanning experience; line-sclerotic artefacts due to uneven mixing of contrast in the right atrium were unavoidable[29], which has an effect on the atrial structure, especially the patent foramen ovale or small atrial septal defect. Conversely, the ventricular wall was less affected and had a higher score (4.25 ± 0.74 vs. 4.78 ± 0.49, 4.08 ± 0. vs. 4.74 ± 0.49). Although the heart valve cannot be dynamically observed similar like TTE, the valve thickening and stenosis under the valve on aortic valves and pulmonary valves were all satisfactorily displayed, which increases our confidence in its role in the diagnosis of heart valve diseases. With the application of the third-generation iterative reconstruction algorithm, the effect of reduced radiation dose on the image-to-noise ratio was effectively offset[30, 31]. Thus, the effect of respiration and cardiac motion on image quality is reduced on third dual-source CT, while the effect of contrast injection parameters and the time of scan start after injection on image quality is incremental and needs further study. For cardiac surgeons, the vascular lumen or tube wall structure is not in their scope of concern and not needed for clinical decision making[32]. In the present study all coronary sinus openings could be clearly visualized, we also observed that the general direction of coronary artery travel could be assessed, but it was difficult to clearly visualize the wall due to the slender lumen.
With surgery as the gold standard, TTE has a higher diagnostic value for intracardiac structures than retro-ECG-triggered or non-ECG-triggered cardiac CTA, with particular advantages in the diagnosis of heart valve disease[33, 34], but a lower diagnostic value in extracardiac structures. Both scanning protocols are effective in detecting both extracardiac and intracardiac malformations, with particularly good diagnostic accuracy for extracardiac malformations. However, cardiac CTA scanning on DSCT is more advantageous. CTA can not only diagnose cardiac developmental malformations but also evaluate the compensatory ability of extracardiac collateral branches for complex CHD, and the respiratory system, such as tracheal dysplasia and pulmonary exudative lesions, and provide an image basis for preoperative evaluation and postoperative care.
Despite our findings, this study has certain limitations. First, this was a retrospective study with a relatively small sample size, which cannot objectively reflect the influence of heart rate at different heart rate stages on the quality of scanned images. Second, in our study, the rate variation was small, and few of the children with arrhythmia were included. Thus, we could not evaluate the image quality of CHD under arrhythmia. Third, the radiation dose was related to TC, which is related to the reference tube current, to achieve a balance between radiation dose and image quality. Thus, the optimal reference tube current still needs to be further studied. In conclusion, high-pitch non-ECG-triggered cardiac CTA of children with high heart rate and CHD can obtain images of a quality that fully meets diagnostic requirements and be used for an accurate diagnosis of intracardiac and extracardiac malformations,it can greatly reduce the cumulative radiation in children with CHD.