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目的 探讨256层螺旋CT前置门控冠状动脉CTA成像中应用迭代重建时,与常规剂量滤波反投影(FBP)重组图像质量相当的最适低剂量水平.方法 120例拟行冠状动脉CTA检查者按照同期随机原则分为4组,每组30例.A组(对照组)采用常规剂量前置门控扫描及FBP重组,B～D组为低剂量组,采用逐级降低管电流的方式使辐射剂量较A组分别降低50％、60％、70％,并采用相应等级的迭代重建.采用方差分析比较各组客观评价指标(噪声、对比噪声比)及辐射剂量(CT剂量指数、CT剂量长度乘积、有效辐射剂量)的差异.采用Kruskal-Wallis检验比较各组主观图像质量评分(管腔对比度、边缘锐利度、主观噪声及图像总体质量,采用4分法).利用ROC曲线确定能维持图像质量等同于A组的最适低剂量组.结果 低剂量B～D组噪声为33.2～ 36.0 HU,低于常规剂量A组(37.4 HU),但差异无统计学意义(F=1.48,P=0.22).B～D组对比噪声比为15.3～16.5,高于A组(15.0±2.3),但各组间差异无统计学意义(F=1.70,P=0.17).B、C组显示了很好的主观图像质量,各项主观评分均≥3分,与A组(主观评分均≥3分)差异无统计学意义(P=0.31 ～ 1.00).D组血管边缘锐利度及总体图像质量(2分均有3例)下降,与A组(均无2分)差异有统计学意义(P＜0.05).ROC曲线显示,C组为维持图像质量等同于常规剂量的最适低剂量组,曲线下面积为0.76,95％可信区间为0.65 ～0.87.该组有效辐射剂量值为(1.2±0.1)mSv,较A组剂量(3.1±0.6)降低约61％.结论 迭代重建可以显著降低噪声,在剂量降低61％的条件下仍可得到与常规剂量FBP重组相当的图像质量.由此,可使患者的冠状动脉CTA辐射剂量降至1.2 mSv.

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.