采集时间窗对冠状动脉CT图像质量及辐射剂量的影响

Effect of Acquisition Window on Image Quality and Radiation Dose in Coronary Computed Tomography Angiography

目的探讨冠状动脉CT成像(CCTA)最佳重建期相随心率变化的规律。依据结果设置最佳采集时间窗,并计算其降低辐射剂量的能力。方法回顾性分析2016年11月至2017年10月以心功能分析为检查目的接受全心动周期全剂量CCTA的616例患者资料。由2名诊断医师确定最佳重建期相,分析最佳重建期相随心率变化的规律。依据此结果设定根据心率决定的窄采集时间窗模式。采集时间窗位于最佳重建期相的平均值±标准差×2,即95%置信区间。计算此采集模式较全心动周期采集模式降低辐射剂量的程度。结果 616例受检者,心率(71±14)次/分(42～149次/分)。低心率组(<61次/分)最佳重建期相:(76±3)%RR间期,95%置信区间:70%～82%RR间期;中心率组(61～75次/分)最佳重建期相以60%RR间期为界位于(44±3)%及(76±3)%RR间期,95%置信区间:38%～50%RR间期及70%～82%RR间期;高心率组(>75次/分)最佳重建期相:(48±5)%RR间期,95%置信区间:38%～58%RR间期。以95%置信区间作为采集时间窗,较全心动周期采集模式降低CTDIvol约80%(低心率)、56%(中心率)、70%(高心率)。结论慢心率者冠状动脉运动相对静止期位于舒张中末期;高心率者位于收缩末期;中心率者位于收缩末期或舒张中末期。以最佳重建期相95%置信区间作为采集时间窗,可以在保证图像质量的前提下缩短曝光时间从而降低辐射剂量。

Objective To determine optimal reconstruction phase in relation to heart rate(HR). On the basis of these findings,an optimal acquisition window was designed,and the potential dose-saving effect was calculated. Methods 616 CCTA exams were performed(HR 71±14 bpm;range 42–149 bpm) using a wide acquisition window(0%–100% of the RR interval). Optimal reconstruction phases were determined by two observers. Based on the findings,a narrow HR-dependent acquisition window was centered at the mean of optimal reconstruction phase with a symmetric width of 2 standard deviation(SD)(95% confidence interval). The potential of dose-saving was calculated by comparing the volumetric CT dose index(CTDIvol) of different acquisition windows. Results At low HR(<61 bpm,133 patients),high-quality data sets were obtained during(76±3)% of the RR interval;at high HR(>75 bpm,190 patients),they were obtained during(48±5)%;and at intermediate HR(61–75 bpm,293 patients),they were obtained during either(44±3)% or(76±3)%. Based on the results above,narrow acquisition windows for low,high and intermediate HR were at 70%–82%,38%–58%,and both 38%–50% and 70%–82% of the RR interval,respectively. With narrow windows,the CTDIvol was decreased at low HR by around 80%,at intermediate HR by 56%,and at high HR by about 70%. Conclusion With narrow HR-dependent acquisition windows,radiation dose can be reduced with preserved image quality.