Application Of Prospective ECG-Gated High-Pitch Spiral Dual-Source CT Angiography In The Diagnosis Of Children With Tetralogy Of Fallot

Chapter Ⅰ : Application of prospective ECG-gated high-pitch spiral dual-source CT angiography in children with congenital heart disease.Objective: To investigate the feasibility of prospective ECG-gated high-pitch acquisition using dual-source CT(DSCT) angiography in children with congenital heart disease(CHD). Comparing with prospective ECG-gated sequential acquisition,the image quality, diagnostic accuracy and radiation dose were evaluated.Materials and methods: Of 88 cases suspected with CHD, 86 cases underwent examination successfully,at last 67 cases confirmed by surgery were included in the study. Thirty-four patients were examined with DSCT angiography with sequential mode, and the other 33 patients examined with high-pitch mode. The study was approved by the institutional review board and informed consent was signed by legal guardian before examination. Patients underwent examination after sedation with uncontrolled heart rate. CT parameters were as follows: 2×64×0.6 mm detector collimation, a slice collimation 2×128×0.6 mm by z-flying focal spot technique,gantry rotation time 0.28 s, weight adapted setting for tube voltage and tube current(70k V for children ≤ 5 kg body weight, 80 k V for children >5 kg body weight; 60 m As/rotation for children < 5 kg body weight, 60-79 m As/rotation for children5-10 kg body weight, 80-120 m As/rotation for children >10 kg body weight). In the high-pitch group, ECG-triggered phase starting at 10% R-R interval with the pitch of3.4. In the sequential group, ECG-triggered window was set at 40%-40% R-R interval.After CT scan, all data with reconstruction slice thickness 0.6 mm,interval 0.5 mm,SAFIRE algorithm(strength 2), soft tissue convolution kernel I26 f were processed in Siemens Syngo workstation. All images were analyzed by two experienced ultrasound doctors with blind method, intracardiac structures, great vessels and the proximal and middle segments of coronary arteries were described using a five-point scale. The CT attenuation, the noise and signal-to-noise ratio(SNR) in the left ventricle, right ventricle, ascending aorta and the pulmonary trunk were measured and calculated.With surgical results as the standard, the diagnostic accuracy of the two groups for the cardiovascular abnormalities was evaluated. The auto-result of DLP was corrected to match 16cm-length phantom, and the ED was calculated.Results: Regarding to the sex, the age, body weight and heart rate of children, the two groups were adequately matched. The high-pitch group had significantly shorter scanning time(t=38.057, P < 0.05) than sequential group. The agreement for the image quality scoring of all evaluated structures between the two observers was excellent. There was no significant difference(u=552.50, P>0.05) between the two groups. The image quality of intracardiac structures and coronary arteries was significantly lower in the high-pitch group than that in the sequential group(u=313.00 and 205.50, P<0.05). The CT attenuation(t=0.811、0.565、0.697、1.149,P>0.05),the noise(t=1.705、1.644、1.009、1.353,P>0.05) and the SNR(t=1.393、1.292、1.784、1.399,P>0.05) in the ascending aorta, the pulmonary trunk, left ventricle and right ventricle had no significant difference between two groups. Taking surgical results as the reference standard, we confirmed a total of 57 and 62 intracardiac anomalies in high-pitch group and sequential group, respectively. The diagnostic accuracy of high-pitch group and sequential group was 89.47% and 93.55%,respectively, without significant difference(χ2= 0.635, P>0.05). A total of 64 and 61 great vessles anomalies were confirmed in high-pitch group and sequential group,respectively. The diagnostic accuracy of high-pitch group and sequential group were93.75% and 95.08% respectively with no significant difference(χ2=0.104, P>0.05).Mean DLP in high-pitch group and sequential group were 7.06±2.42 m Gy?cm,10.12±3.15 m Gy?cm, and mean ED were 0.36±0.08 m Sv、0.51±0.08 m Sv in the two groups, respectively. Both DLP and ED in high-pitch group and sequential group had statistically significant differences(t=4.468、8.200,P<0.05). The DLP in high-pitch group were lower than that in sequential group by about 30%.Conclusion: The prospective ECG-gated high-pitch acquisition of dual-source CT in pediatric cardiology examination is safe and feasible, Which has high accuracy for the various internal and external cardiac malformations. Compared with prospective ECG-gated sequential acquisition, while declined in some image quality of prospective ECG-gated high-pitch acquisition, but it has significantly lower radiation dose.Chapter II Diagnosis of tetralogy of Fallot of children by dual-source CT angiographyObjective: To investigate the value and accuracy of prospective ECG-gated high-pitch acquisition on dual-source CT(DSCT) angiography in the diagnosis of children with tetralogy of Fallot and associated anomalies in comparison with transthoracic echocardiography(TTE) and surgical results.Materials and methods: The study was approved by the institutional review board and the informed consent was signed. Fifty-eight consecutive children clinically suspected with tetralogy of Fallot were included in this prospective study, and CT examination were recorded within 7 days after TTE. 40 patients undergoing surgical correction were finally enrolled, including 23 males and 17 females, with the age ranged from 2 months to 5 years, the mean age of 18.15±13.03 months, the median age of 12 months, and the mean body weight of 9.48±5.01 kg. All patients underwent prospective ECG-gated high-pitch DSCT angiography after sedation with uncontrolled heart rate. CT parameters were were set to be similar to the first chapter of this paper. After CT scan, all data with recontruction slice thickeness 0.6m,interval0.5mm, SAFIRE algorithm(strength 2), soft tissue convolution kernel I26 f were processed in Siemens Syngo workstation. All patients underwent two-dimensional TTE and Color Doppler imaging using a Siemens Sequoia 512 ultrasound system.The examinations were performed by two experienced echocardiographic technicians together. Two ultrasound doctors of clinical experience in cardiovascular disease analyzed all images blindedly, and evaluated image quality of CT using a five-point scale. The basic and associated anomalies of TOF were analyzed respectively.According to the surgical findings, the study compared dimension of the right ventricular outflow tract, pulmonary valve ring, the main pulmonary artery, bilateral pulmonary arteries, ventricular septal defect, described the basic malformations characteristics, and evaluated the accuracy of double oblique MPR assessing degree of aortic overriding. We recorded the diagnosed number, the number of misdiagnosis and missed number of DSCT and TTE in variety of associated malformations, and compared the diagnostic accuracy of DSCT, TTE and their combination.Results: A total of 40 children were enrolled, with the mean heart rate of 114.48±17.70 bpm and the mean scan time of 0.44±0.06 s. The score of total image quality was 3.9±0.8, which was enough for diagnosis, and the agreement on the image quality scoring of DSCT between the two observers was excellent(κ=0.82). The mean ED of DSCT was 0.35±0.12 m Sv. Both DSCT and TTE were consistent with the surgery(P>0.05) in evaluating dimension of the right ventricular outflow tract, pulmonary valve, and the main pulmonary artery. There was no significant difference between the two methods(P>0.05). The two methods had good consistency with the surgery in evaluating dimension of bilateral pulmonary artery, ventricular septal defect( P >0.05), while results of DSCT were greater than that of TTE with significant difference between the two methods(P<0.05). Double oblique MPR of DSCT was consistent with the surgery in assessing degree of aortic overriding, while 3 cases in TTE were greater 5% than that of surgery, 2 cases in TTE were lower 5%. There were a total of61 associated malformations in 40 cases of TOF, including 17 intracardiac malformations and 44 extracardiac malformations. DSCT failed to identify 5 atrial septal defect(5/12), 1 coronary artery abnormality(1/2), 2 high origin of pulmonary collateral circulation(2/23). TTE misdiagnosed 13 extracardiac malformations(13/44)and only 1 small atrial septal defect in intra-cardiac malformations(1/2). DSCT confirmed more extracardiac malformations than TTE with significant difference(P<0.05),but in confirming the intracardiac malformations, the two examine method had no significant difference(P>0.05). The accuracy of DSCT and TTE, DSCT and combined examination had no significant difference in the diagnosis of associated malformations in TOF(χ2 =2.000、3.890,P>0.05). Accuracy of the two combined examination was greater than that of TTE(χ2=10.270,P<0.05).Conclusion: Prospective ECG-gated high-pitch dual-source CT angiography with low radiation dose could demonstrate basic malformations of TOF excellently, and does better in diagnosis of extracardiac associated anomalies than TTE. The two combined examination can improve the accuracy of associated anomalies with the diagnostic accurate of 96.72%.