80kV64排多层螺旋CT低辐射肺动脉成像

Minimizing radiation dose of pulmonary angiography with 80 kV 64-row multidetector CT

目的研究80kV管电压64排多层螺旋CT低辐射肺动脉成像的可行性。方法64名志愿者随机分为2组。观察组35例采用80kV管电压CT结合右头臂静脉作为团注追踪（bolustracking）监测点进行肺动脉成像，对照组29例采用120kV管电压，延迟时间采用团注测试峰值时间＋0．7s，进行肺动脉成像。测量容积CT剂量指数（CTDIvol）、剂量长度乘积（DLP），计算加权CT剂量指数（CTDIw）和有效剂量（E），测量肺动脉强化后CT值和背景噪声，计算信噪比（SNR）和对比噪声比（CNR）。5分法对两组图像质量进行目测评分。对DLP、E、SNR、CNR进行t检验；采用Mann—Whitney U检验比较两组图像目测评分结果。结果观察组DLP和E分别为（146．5±7．6）mGv·cm和（2．5±0．1）mSv，对照组DLP和E分别为（313．4±13．5）mGy·cm和（5．3±0．2）mSv，两者差异有统计学意义（P〈0．001），观察组的辐射剂量低于对照组。图像质量量化评价：观察组和对照组的SNR分别为32．6±3．6和31．35±2．0，差异无统计学意义（P=0．089）。观察组和对照组CNR分别为28．5±3．4和27．6±1．1，差异无统计学意义（P=0．18）。目测评分结果：观察组为5分8例，4分26例，3分1例；对照组为5分5例，4分24例，差异无统计学意义（P=0．76）。结论80kV64排多层螺旋CT结合右头臂静脉作为bolus tracking监测点可以减少辐射剂量，同时不降低图像质量，是肺动脉造影的首选检查方法。

Objective To assess the feasibility of minimizing radiation doses using 80 kV 64-row muhidetector computed tomography on pulmonary angiography. Methods 64 volunteers were devided into 2 groups to undergo MDCT pulmonary angiography （collimation, 64 × 0.625 mm; pitch, 1. 204 ）. The observed group consisting of 35 patients were for pulmonary angiography with 80 kV voltage, 300 mAs, O. 75 s/roation. The control group consisting of 29 patients were for pulmonary angiography with the standard tube voltage （120 kV）, 200 mAs, 0.5 s/roation and time delay using the peak time on bolus test added 0.7 s. Volume computed tomography dose index （CTDIvol）, dose length product （DLP）, pulmonary vessel enhancement and back noise were quantified. Signal-noise-ratio （ SNR ）, contrast-to-noise-ratio （ CNR ）, weighted computed tomography dose index （CTDIw） and effective dose （E） were calculated. Results of the two protocols were compared by using t test. Two radiologists used five-point scale to subjectively score arterial enhancement and depiction of small arterial detail. The scores were compared with Mann-Whitney U test. Results The 80 kV protocol had a significantly lower DLP and E than the 120 kV protocol [ （146.5 ± 7.6） mGy＇cm vs （313.4 ± 13.5） mGy·cm, P〈0.001] and [（2.5±0.1） mGy vs （5.3±0.2） mGy, P〈0.001], respectively. The 80 kV protocol and the 120 kV protocol had identical SNR（32.6 ±3.6 vs 31.3 ± 2.3; P = 0.089） and CNR （28.5 ± 3.4 vs 27.6 ± 1.1 ; P = 0.18）. No significant difference was found between the two protocols on scores for arterial enhancement and depiction of small arterial detail （ P = 0.76）. Conclusions 80 kV 64 slices MDCT combined with right brachiocephalic vein as the monitoring site for bolus tracking could be the first choice of pulmonary angiography. It can reduce the radiation dose without sacrificing the image quality.