双源大螺距螺旋CT心冠状动脉超低剂量扫描及其图像质量的研究

Image Quality of Coronary Computed Tomographic Angiography Using Ultra-Low-Dose, High-Pitch, Dual Source CT Technique

目的：探讨大螺距冠状动脉扫描模式下，使用超低剂量扫描对图像质量的影响。方法对连续33例心率≤65次/min的中等身材患者进行前瞻性心电触发大螺距螺旋CT扫描冠状动脉造影。33例患者随机分成两组：A组12例、B组21例。A组使用120 kV，B组使用100 kV，探测器使用128×0.6 mm，转速0.28 s/r，前瞻性心电触发选在60%R-R间期，螺距为3.4。图像质量分别采用4级评分法（1=不可评价，4=优秀）和计算两组图像主动脉根部、前降支近端、回旋支近端、右冠近端的信噪比（SNR），对比噪声比（CNR），计算公式为：SNR=所测部位CT值/所测部位SD值，CNR=（所测部位CT值-胸大肌处CT值）/空气的SD值。结果1、A、B两组的平均辐射剂量（ED）分别为1.72 mSv和0.78 mSv，B组的患者所受辐射剂量为A组的45%，差异有统计学意义（P＜0.05）。2、在B组辐射剂量明显低于A组的情况下，A组总得分为640分，平均每段得分为3.86分，B组总得分为1,144分，平均每段得分为3.85分，采用Mann-Whitney U检验P=0.889，差异无统计学意义，A、B两组在主观评价时无质量区别。3、计算各点的SNR和CNR，从均值分析A组的SNR略高于B组，其CNR略低于B组，但通过均值方程的t检验发现差异无统计学意义（P＞0.05），即A、B两组的冠脉图像质量从客观数据分析无明显区别。结论大螺距冠脉扫描模式下，对于中等身材的患者来说，可以通过降低管电压的方法来进一步降低辐射剂量，达到心脏冠脉的超低剂量扫描。

Objective To investigate the image quality of prospectively electrocardiogram-triggered spiral by ultra-low-dose for coronary computed tomographic angiography （CCTA） using dual-source computed tomography.MethodsThirty three patients in total with a stable heart rate （HR）≤65 bpm and medium build underwent CCTA. Patients were randomly divided into two groups （A=12, B=21）. A dual-source CT scanner was used （0.6 mm collimation, 0.28 s rotation time, A=120 kV, B=100 kV）. Date acquisition was prospectively ECG-triggered at 60%of the R-R interval with a pitch of 3.4. Subjective image rating used a four-point scale （1=unevaluable, 4=excellent）. Objective image quality was evaluated by calculating SNR and CNR for aortic root, proximal left anterior descending artery, proximal circumfl ex artery, and proximal right coronary.Results 1.Average radiation dose （ED） was 1.72 mSv for group A and 0.78 mSv for group B. The radiation dose for group B decreased 55% than group A （P〈0.05）. There were significant differences between them. 2.Average scores of coronary segment were 3.86 for group A and 3.85 for group B. Using the Mann-WhitneyU test, the rating of evaluable segments showed no significant difference between the two groups （P=0.0889）. 3.Coronary quality from objective data analysis showed no signifi cant difference between the two groups （SNR and CNR,P〉0.05）. Conclusion Prospectively electrocardiographic triggered high-pitch spiral acquisition by dual-source for patients of medium build can be practiced by reducing the tube voltage to further reduce the radiation dose to achieve ultra-low-dose coronary heart scan.