256层CT前瞻性及回顾性心电门控ECG电流调制技术的应用

摘要

目的：探讨256层CT前瞻性及回顾性心电门控ECG电流调制技术图像质量及辐射剂量，探讨其临床应用价值。方法：160例患者分为3组：A组50例，采用回顾性心电门控技术，关闭ECG电流调控；B组50例，采用回顾性心电门控螺旋扫描，开启ECG电流调控；C组60例，采用前瞻性心电门控横轴面扫描，心率≤70次/分(32例)时数据采集时间窗设在R-R间期75％时相，心率＞70次/分(28例)时，数据采集时间窗设在45％～50％R-R间期。冠状动脉分段采用美国心脏协会(AHA)15分段法，采用3分法评价图像质量，3分为优，2分为中等，1分为差，其中≥2分为合格。在横轴面图像上左冠状动脉主干自左窦发出的层面测量升主动脉中心部的噪声值。对3组图像质量评分、图像噪声、容积CT剂量指数(CTDIvol)、剂量长度乘积(DLP)、有效剂量(ED)进行方差分析。结果：①三组图像质量评分中，A组中99.3％节段(609/612)为可评价节段，B组为99.1％节段(607/615)，C组为98.9％节段(732/740)，三组间差异无统计学意义(P＞0.05)；②心率≤70次/分和＞70次/分时3组可评价率无明显差异，但心率＞70次/分时A、B组优秀率无差异，但A组与C组、B组与C组冠脉段数的优秀率有差异；③三组图像噪声值分别为32.95士5.49、32.7士5.14和33.47士5.5，三组间差异无统计学意义(P＞0.05)；④三组CTDIvol均值分别为(62.52±4.67)、(50.56±9.76)和(17.47±7.42)mGy，三组ED值分别为(15.3±1.44)、(13.05±2.34)和(3.06±1.23)mSv。B组有效剂量比A组减少约13％，C组比A组有效剂量减少约80％，三组间差异有极显著性意义(P＜0.01)。结论：采用前瞻性心电门控技术显著降低辐射剂量且不受心率的影响，当需要进行心功能分析或心瓣膜痛动态观察时，可以采用ECG电流调制技术降低辐射剂量。%Objective:To evaluate the impact of prospectively ECG-triggered and retrospectively ECG-gated coronary artery CT angiography (CTA) with milliampere (mA) modulation using a 256-slice CT (MSCT) on image quality and radiation dose. Methods: One hundred and sixty patients undergoing 256-slice coronary CTA were divided into three groups: Group A (50 patients) ,with retrospectively ECG-gated technique,yet with no mA modulation;Group B (50 patients) ,with retrospectively ECG-gated technique and mA modulation) Group D (60 patients, with prospectively ECG-triggered axial scan. In group C,32 patients with an average heart rate (HR) of ≤70bpm were scanned with a data acquisition window centered at 75% of the R-R cycle and 28 patients with an average heart rate of >70bpm were scanned with the data acquisition window centered at 40%~50% of the R-R cycle. The coronary artery was segmented according to the American heart association (AHA) 15 segment classification,3 grade system was used to evaluate the image quality,excellent (3 scores) .medium (2 scores) and is poor (1 score). ≥2 grades were regarded to be qualified. Image noise was measured at the center of ascending aorta arising from the left sinus on axial scan, the differences of noise of these 3 groups were compared. The CT dosage index-volume (CTDIvol),dosage length product (DLP) .effective dose (ED) of these three groups were recorded,k= 0. 014. Statistical analyses were performed for the comparison of image quality, noise, CTDIvol ,DLP and ED. Results ①As for the image quality,the rate of segment evaluated was 99. 3% (608/612 segments),99. 1% (609/615 segments) and 98. 9% (732/740 segments) .respectively,with no significant statistical differences (P>0. 01). ②As for the rate of excellence, there was no significant statistic difference in these 3 groups, when the average heart rate was >70bpm or ≤70bpm. Yet as heart rate ≥70bpm,no statistic difference was existed in the rate of excellence between Group A and Group B.but did existed between Group A and Group B as well as Group A and Group C. ③The values of noise measured in these three groups were 32. 95±5. 49,32. 7±5. 14 and 33. 47±5. 54,respectively, with no significant difference (P>0. 01). ?The CTDIvol, and ED values were (62. 52±4. 67)mGy and (15. 3±1. 44)mSv,(50. 56±9. 76)mGy and (13. 05±2. 34)mSv,(17. 47± 7. 42)mGy and (3. 06±l. 23)mSv,respectively, with significant differences in the three groups (P<0. 01). The radiation dose of Group B was 13% lower than that of Group A and the radiation dose of Group C was 80% lower than Group A. Conclusion:Using prospectively ECG-triggered axial scan with 256-slice CT,radiation dose and the impact of undesired heart rate could be significantly reduced. ECG mA-modulation technique could be used to reduce the radiation dose when cardiac function analysis or dynamic observation of cardiac valve disease were needed.