Application of iterative reconstruction in prospective electrocardiography-triggered CT coronary angiography

Objective: To assess the image quality (IQ) of an iterative reconstruction (IR) technique (iDose⁴) from prospective electrocardiography (ECG)-triggered coronary CTA on a 256 MSCT scanner and determine the optimal dose reduction using IR that can provide IQ comparable to filtered back projection (FBP). Methods: Prospectively ECG gated CCTA were performed on 120 patients [76 men, 44 women; age: (53 ± 10) y] using a 256-slice MSCT (Brilliance iCT, Philips Healthcare). The control group (Group A , n = 30) were scanned using the conventional tube output (120 kVp, 210 mAs) and reconstructed using FBP. The other 3 groups were scanned with the same kVp but successively reduced tube output as follows: B (n = 30) : 105 mAs , C (n = 30) : 84 mAs: D (n = 30) : 65 mAs and reconstructed using IR levels of L4 to L6, respectively. All images were reconstructed using the same kernel (XCB). Two radiologists graded IQ in a blinded fashion on a 4-point scale (4-excellent, 3-good, 2-fair and 1-poor). Quantitative measurements of CT values, image noise, Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were obtained in each group. Analysis of variance (ANOVA) was used for comparisons of objective evaluation indices (noise, CNR) and radiation dose (CTDIvol, DLP, ED) between the four groups. The Kruskal-Wallis test was used for comparisons of demographic data and for detection of differences in subjective evaluation of IQ among groups. A level of P < 0.05 was considered statistically significant. A ROC analysis was performed to determine a radiation reduction threshold up to which excellent IQ was maintained. Results: There was no significant differences in objective noise among Groups A (37.4 ± 7.9) HU, B (33.2 ± 7.1) HU, C (35.7 ± 9.8) HU, and D (36.0 ± 6.8) HU (F = 1.48, P = 0.22). There was no significant differences in CNR among Groups A (15.0 ± 2.3), B (16.5 ± 3.6), C (16.3 ± 3.5), and D (15.3 ± 2.8) (F = 1.70, P = 0.17). Group B and C had good and excellent scores of the subjective IQ (≥ 3), and there was no significant differences in the scores of the subjective IQ between Group A, and Groups B, C (P = 0.30-1.00). Significant differences in image sharpness and study acceptability were observed between groups A and D (P < 0.01). Using the criterion of excellent IQ (score 4), the ROC curve of dose levels and IQ acceptability established a reduction of 60% of tube output (Group C) as optimum cutoff point (AUC: 0.76, 95% CI: 0.65-0.87). The effective dose (ED) of Group C was 61% lower than that of Group A, (1.2 ± 0.1) mSv vs. (3.1 ± 0.6) mSv. Conclusion: Iterative reconstruction techniques can provide 61% ED reduction in prospectively-triggered coronary CTA using 256-slice MSCT while maintaining excellent image quality. (authors)