64层螺旋CT心脏成像获得一致噪声及控制辐射剂量的个体化管电流选择方法

A method to optimize the selection of tube current for consistent image noise and dose control in 64-sfice spiral helical CT cardiac imaging

目的探讨根据患者个体差异调整管电流（mA），获得一致64层螺旋CT冠状动脉血管成像（CTCA）的图像噪声，进而控制辐射剂量的方法。方法（1）80例患者作为固定mA组（650mA）以一致的扫描条件进行64层螺旋CTCA检查。2名医师用5分法评价固定mA组的噪声水平以确定诊断图像质量所需要的噪声水平标准差（SD）SD。值，并建立一个少量对比剂团注探测循环时间扫描（TB）噪声SDT8值和心脏扫描（CA）达到SD0水平所需mA的关系式。（2）80例64层螺旋CTCA检查根据个体差异调整扫描mA，作为个体mA调制组与固定mA组进行比较，分析该方法的可操作性和辐射剂量的控制，两组均数比较用独立样本t检验。结果（1）固定mA组的TB和CA的噪声SD呈线性相关（r2=0．994）；（2）根据主观评价的结果将SD0定为28HU可获得满意的图像质量；（3）个体mA调制组噪声平均值28．97HU，SD为1．93，小于固定mA组的5．14，但质量评分（4．27±0.68）与固定mA组（4．03±0．93）差异无统计学意义（P〉0．05）；（4）个体mA调制组63例调整后〈650mA，平均CT剂量指数（CTDIv01）为58．32mGy，比固定mA组（85．94mGy）减少了32．1％，其中1例患者仅使用160mA，CTDIvol=19．27mGy，是固定mA组平均剂量的22．4％。结论通过个体的TB噪声SD调整mA可获得一致心脏扫描噪声水平，是有效的实用的保证成像质量又对个体辐射剂量进行控制的方法。

Objective To establish and clinically evaluate a method to adjust tube current （mA） individually for obtaining images with consistent noise and optimized radiation dose in 64-slice spiral helical CT coronary angiography. Methods （1） 80 patients, as a control group, were underwent CT coronary angiography （CTCA） using 64-muhislice spiral helical CT with fixed mA （650 mA）. Two radiologists first assessed image quality of the fixed mA group by scoring from 1 to 5. A minimal dose requirement for meeting clinical diagnosis with the desired noise level （ standard deviation SD0 ） were decided. By analyzing the images of the control group, we also established correlation between the image noises of timing bolus （TB） scans and cardiac （CA） scans and set up a formula to predict the required mA value for obtaining the desired cardiac image noise for individual patient. （2） Subsequently, another group of 80 patients （ study group） were scanned with individually adjusted mA using the established formula and the practicability of this method was then evaluated. The independent sample t test was used to compare the values of the two groups. Results （ 1 ） The noise of TB and CTCA scans was linearly correlated with r2 = 0. 994. （2） A cardiac image noise level of 28 HU was found to be adequate for clinical diagnostic purpose based on the image quality analysis. （3） The average noise for the acquired cardiac images was found to be 28.97 HU for the study group with individually adapted mA using the established formula. The standard deviation of the image noise in study group was 1.93, which was much smaller than 5.14 in the fixed mA group, bui the average image scores for the study group （ 4. 27 ±0. 68 ） and fixed group mA （4.03 ± 0. 93 ） were not statistically different. （4） In the study group, 63 out of 80 patients required tube currents below the standard 650 mA, yielding an average CTDIvol of 58.32 mGy, which was about 32. 1% dose reduction than that of fixed mA（85.94 mGy）. The lowest CTDIvol was 19.27 mGy with 160 mA which was 22. 4% of the average CTDIvol in control group. Conclusion Adjusting mA individually based on timing bolus scan noise analysis is an accurate and practical method to obtain consistent image quality for different cardiac patients and to minimize the radiation dose for individuals compared to the fixed mA.