64层螺旋CT心脏检查中体重指数与射线剂量关系的研究  

Body mass index adapted tube current selection in 64-row MSCT coronary artery imaging

作　　者：王贵生[1] 高建华[1] 李剑颖[2] 叶道斌[1] 张如意[1] 李娜[1] 

机构地区：[1]武警总医院CT科,北京100039 [2]GE中国CT影像研究室,北京100176

出　　处：《医学影像学杂志》2008年第5期473-477,共5页Journal of Medical Imaging

摘　　要：目的：在64层螺旋CT心脏检查中，通过对不同体重指数（BⅦ）采用不同射线剂量的研究，达到均衡控制射线剂量的目的。方法：实验分2个步骤进行：①连续选取100例（C组）拟行64层CT冠状动脉成像的患者（不限身高体重），使用CE Lisht Speed VCT机完成心脏扫描。采用640mA，120kV，0．35s／r，层厚0．625mm，pitch0．22—0．24，Bowtie选用large body模式，后过滤C2重建。采像后在主动脉分出冠状动脉左主干的层面上下三层，以像素100mm^2大小测量图像噪声，取三层的平均值作为该病人的图像噪声；之后使用软件拟合患者BMI和噪声的关系，得出线性方程；根据噪声和射线剂量的公式。在噪声等于27得到BMI和管电流量的对应值；②再连续选取100例（E组）拟行64层CT冠状动脉成像的患者（不限身高体重），先计算其BMI值，根据之前得到的BMI和管电流量对应值确定扫描时mA值，其它扫描参数与前一致：120kV。0．35s／r，层厚0．625mm。pitch0．22-0．24，Bowtie选用largebody模式，后过滤C2重建，以同法计算图像噪声。结果：①c组BMI25．08±2．64，心率62．03±9．72，Pitch0．23±0．03，噪声24．56±5．03，有效剂量（ED）17．63±1．68mSv，图像质量评分3．71±0．54。拟合不同BMI和噪声的关系，得出曲线回归公式：Y=1．143x-6．0，R^2=0．55（Y为噪声，x为BMI，R^2为决定系数）；根据射线剂量和噪声关系，得出Xma=Fma×{（k1^＊BMI＋C1）／INa}^2，Fma=640mA，k1=1．143，C1=-6．0，INa=27（HU）；②E组BMI25．87±3．16，心率67．20±14．47，Pitch0．23±0．16，噪声26．51±3．76，ED15．25±3．31mSv，图像质量评分3．56±0．74，曝光剂量579．425±125．61mA。E组ED明显低于C组（降低约13％），P〈0．01。结论：在64层CT心脏成像时，对不同体重指数人群采用不同曝光剂量，可在保证图像质量不变的前提下，均衡控制不同体�Objective： To evaluate the robustness of body mass index （BMI） adapted tube current selection method for obtaining consistent image quality for patient population in MSCT coronary artery imaging.Methods：We first analyzed 103 patients （BMI 19 to 33） underwent cardiac scans using GE 64-row VCT with standard scan protocol （120 kV, 640 mA, 0.35 see, body bowtie, C2 filter） to establish the relationship between BMI, desired image noise （IN） and required mA. An excel table was established to predict the required mA to achieve a desired IN for patient of certain BMI. We then scanned 100 cardiac patients with BMI-adapted mA from the table to evaluate the robustness and practicability of this method. We did not use other dose reduction techniques in this study. Two experienced radiologists quantitatively evaluated the image quality in terms of the number of coronary arteries and smaller branches identified, vessel sharpness, and contrast agent clarity using scores of 1 - 4 with 4 being the highest. Effective dose （ED） was recorded and noise was measured for each patient using the average of thrce consecutive slices in the ascending aorta with ROI of 100 mm^2. Results：For the control group of 100 patients, the mean values and standard deviations of image quality score （IQS）, BMI, IN and ED were 3.71 ±0.54, 25.08± 2.63, 24.56 ± 5.02 and 17.63±1.68 mSv; while, for the study group with BMI adapted mA, the corresponding values were 3.56 ± 0.74, 25.87 ± 3.76, 26.51 ± 3.76 and 15.25 ± 3.31 mSv respectively. Statistical analysis indicated no difference for IQS, BMI and IN between the two groups. However, BMI-adapted mA method produced much smaller deviation for the image noise than the fixed mA group （2.63 vs 3.76）. The one-way ANOVA indicated statistically significant lower dose （13 % ） with the use of BMI-adapted mA method due to the use of lower mA for small patients （ P 〈 0.01）. Conclusion：The use of BMI adapted mA selection method is robust and practical to obtain consist

关 键 词：体层摄影术 X线计算机 体重指数 冠状动脉 X线剂量 

分 类 号：R814.42[医药卫生—影像医学与核医学] R322.1[医药卫生—放射医学]