| Part â… Low-dose prospectively ECG-gated axial dual-source CT angiography in patients with pulsatile bilateral bidirectional Glenn shuntObjective:To explore the clinical value of low-dose prospectively ECG-gated axial dual-source CT angiography (low-dose PGA scanning) in patients with pulsatile bilateral bidirectional Glenn shunt (bBDG) as an alternative noninvasive method for post-operative morphologic estimation.Methods:Twenty patients with pulsatile bBDG 6 to 12 months after surgery (mean age 4.2±1.6 years, range 2-6 years; 15 males; mean body weight 15.4±3.7 kg, range 10-21kg) underwent low-dose PGA scanning and conventional cardiac angiography (CCA) within one week. CT parameters were as follows:0.33 s gantry rotation time,2 ×32×0.6 mm detector collimation, a slice collimation 2 X 64 X 0.6mm by z-flying focal spot technique,80 kV tube voltage and weight adapted setting for tube current (10 mAs/rotation per kilogram for patients ≤ 6kg body weight, another 5 mAs/rotation per kilogram for patients >6kg body weight on the basis of 60 mAs/rotation). The acquisition window was set at 40%-40% of the R-R interval.Blinded to the results of surgical and/or CCA findings, two cardiac radiologists with more than 5 years’ experience interpreted the image quality of great vessels using a 5-grade scoring system. The CT attenuation and the noise in the bilateral SVC and PA were measured. The post-operative morphologic evaluation included morphologic measurements of superior vena cava (SVC) and pulmonary artery (PA), the anastomotic relationship between SVC and PA, thrombosis, aorto-pulmonary collateral circulation, pulmonary arteriovenous malformations, and so on. The CT dose index volume and dose length product were recorded to calculate the effective dose of CT angiography (CTA), while dose area product was recorded to calculate the effective dose of CCA. Interobserver agreement on grades of subjective image quality was assessed by kappa statistics. Bland-Altman analysis and linear regression analyses were performed to analyze the correlation between CTA and CCA, and Pearson’s correlation coefficient was calculated.Results:The attenuation of left SVC, right SVC, left PA and right PA was 351.1±52.3HU,353.8±60.4HU,345.7±57.0HU and 356.5±67.6HU, while the noise of left SVC, right SVC, left PA and right PA was 26.4±4.1HU,24.5±5.4HU, 25.2±3.7HU and 24.5±4.4HU. All examinations showed diagnostic image quality, with no examination rated non-diagnostic (5, n=5;4, n=11;3,n=4). The average subjective image quality score was 4.05±0.69, and 4.15±0.67 for reader 1 and 4.00±0.73 for reader 2 respectively. The two reviewers were in good agreement (k =0.76, P<0.05) with the subjective image quality scoring. Low-dose PGA scanning was able to display the morphology of bilateral SVC and PA completely and intuitively. There were 61.5% (24/39) SVC above PA and 38.5% (15/39) SVC beside PA. Thrombosis was found in one patient. A total of 33 APCs were identified by both CCA and CTA among 13 patients (2 in 6 cases,3 in 7 cases). There were no pulmonary arteriovenous malformations in 20 patients. CTA and CCA showed a strong correlation in terms of measurements (R2>0.8, P<0.001). Bland-Altman analysis demonstrated a systematic overestimation of the measurements by CT (the mean value of bias>0). The mean effective dose of low-dose PGA scanning was 0.50±0.17 mSv, while the average effective dose of CCA was 4.85±1.34 mSv.Conclusion:Low-dose PGA scanning is a convenient and noninvasive post-operative method of morphologic assessment for patients with pulsatile bBDG with a very low radiation dosage.Part II Low-dose prospectively ECG-gated high pitch spiral dual-source CT angiography companied with sonogram affirmed iterative reconstruction (SAFIRE) algorithm in patients with bilateral bidirectional Glenn shuntObjective:To explore the clinical value of low-dose prospectively ECG-gated high pitch spiral dual-source CT angiography (low-dose HP scanning) companied with sonogram affirmed iterative reconstruction (SAFIRE) algorithm in patients with bilateral bidirectional Glenn shunt (bBDG) and compare the image quality and radiation of 80 kV and 70 kV.Methods:Forty patients with bBDG were prospectively enrolled. Twenty patients (mean age 5.4±3.0 years, range 1-10 years; 8 males; mean body weight 19.2±6.9 kg, range 10-31kg) were divided into group A, and the other twenty patients (mean age 5.6±2.7 years, range 1-10 years; 9 males; mean body weight 18.8±5.6 kg, range 9-30kg) were divided into group B. Low-dose HP scanning and CCA were performed within one week. CT parameters were as follows:0.28 s gantry rotation time,2×64 ×0.6 mm detector collimation, a slice collimation 2 X 128 X 0.6mm by z-flying focal spot technique. The data acquisition was prospectively ECG-triggered starting at 10% of the R-R interval using a pitch of 3.4. The parameters in group A were 80 kV tube voltage and weight adapted setting for tube current (10 mAs/rotation per kilogram for patients≤6kg body weight, another 5 mAs/rotation per kilogram for patients>6kg body weight on the basis of 60 mAs/rotation). The parameters in group B were 70 kV tube voltage and additional 20 mAs/rotation more than that of the tube current in group A. Two cardiac radiologists with more than 5 years’ experience interpreted the image quality of great vessels using a 5-grade scoring system. The CT attenuation and the noise in the ascending aorta, chest muscles, bilateral superior vena cava (SVC) and pulmonary artery (PA) were measured. The CT dose index volume and dose length product were recorded to calculate the effective dose (ED). Interobserver agreement on grades of subjective image quality was assessed by kappa statistics. The image quality scores were compared by using the Mann-Whitney U test. The student’s t test was performed to analyze the differences between the two groups regarding patient demographics, objective image quality and radiation dose.Results:There was no significant difference between the two group with regard to patient demographics, the mean noise of vessels, SNR and CNR of the ascending aorta (P>0.05). However, the attenuation in group B was higher than that in group A (P<0.05). Overall interobserver agreement on subjective image quality was good (k =0.74,0.75, P<0.05). The average subjective image quality score in two groups was 4.30±0.66 vs.4.15±0.67, and there was no significant difference in the subjective image quality between two groups (u=176.00, P>0.05). The mean ED of two groups were 0.32±0.12 mSv vs.0.25±0.08mSv (t=2.128, P<0.05), and the radiation dose of group B was smaller than that of group A.Conclusion:Low-dose HP scanning companied with SAFIRE is a convenient and noninvasive post-operative method of assessment for patients with bBDG. Since there was no obvious declination in image quality using the tube voltage of 70kV, there is a great clinic prospective of 70kV with regard to the postoperative evaluation of patients with bBDG. |
