噪声关联Z轴管电流调制技术降低多层CT胸部扫描辐射剂量的作用

目的 评价噪声关联z轴管电流调制技术降低多层CT胸部扫描的辐射剂量、提高图像质量(信噪比水平)的效果.方法 连续200名CT定位像未显示明显胸部异常的受检者,按前瞻性的研究方法 进行分组,根据检查顺序的单双数随机分为z轴管电流调制组(单数者为试验组)和管电流固定组(双数者为对照组),每组100名.试验组的目标噪声水平设置为10.0 HU,扫描设备根据定位像扫描时获取的胸部密度信息自动设置扫描时的动态管电流值;对照组的管电流设置为200 mA,其他扫描参数与试验组完全相同.分别记录2组的最大管电流、CT剂量容积(CTDIv01)、剂量长度乘积(DLP)和女性乳房最大层面的管电流值;测量肺尖、主动脉弓、左心房和肺底层面的图像噪声.图像质量分3级(优、良、差),由2名有经验的CT技师采用双盲法评价.计数资料采用成组设计的x2检验,计量资料采用成组设计的t检验,P<0.05为差异有统计学意义.结果 试验组的最大管电流、CTDIvol、DLP和乳房最大层面管电流的平均值分别为(178.5±125.6)mA、(10.5±3.8)mGy、(231.6±24.3)mGy/cm和(116.0±22.5)mA;对照组的分别为200.0 mA、12.8 mCy、(274.7±18.4)mGy/cm和200.0 mA,试验组较对照组分别降低10.8%、19.9%、15.7%和42.0%,两组差异有统计学意义(P值均<0.05).试验组肺尖和肺底层面的图像噪声分别为10.5和10.4 HU,明显低于对照组的15.3和15.6 HU;图像质量优的数量大幅增加.结论 噪声关联z轴管电流调制技术实现了受检者个性化适应性曝光,在胸部扫描时可明显降低受检者的整体辐射剂量,并提高图像质量.

The function of Z-axis tube-current modulation technique with desired noise level to decrease radiation dose in MSCT chest scanning

Objective Retrospectively evaluate the effect of Z-axis tube-current modulation technique with desired noise level to improve image quality (image noise level) and decrease radiation doses of MSCT (16-slice CT) in chest scanning. Methods Consecutive two hundred patients whose CT scan projection radiographs showed no significant abnormal were randomly divided into two groups by the examination order: Z-axis tube-current modulation (ZTCM) group (odd number, test group) and constant tube-current (CTC) group (even number, contrast group). The desired noise level of ZTCM group was 10HU and the machine automatically set the dynamic tube-current in scanning according to attenuated information of chest acquired in scan projection radiographs, the tubo-current of CTC group was set at 200mA, while the other scan parameters remained totally the same. The maximum tube-current value,CTDIvol, DLP and the tube-current of the slice at the maximum breast level of female patients were recorded respectively. The noise of image at upper lung, aorta arch, left atrium and bottom lung level were measured and compared. The qualities of Images were classified in three levels (excellent, good, poor) with double blind method. Results The mean value of maximum mA, CTDIvol, DLP and mA of the slice at the maximum breast level of ZTCM group were (178.5±125.6) mA, (10.5±3.8) mGy, (231.6±24.3)mGy/cm and (116.0±22.5) mA, those of CTC were 200.0 mA, 12.8 mGy, (274.7±18.4)mGy/cm and 200.0 mA, ZTCM group decreased by 10.8%, 19.9%, 15.7% and 42.0%,respectively, as compared with CTC group. The image quality at upper lung and bottom lung level in ZTCM group was improved significantly (P < 0.05) and the cases of excellent images in ZTCM group was significantly higher than that of CTC group (P < 0.05). Conclusion ZTCM technique not only contributes to more rational distribution of radiation doses but also realizes individuation, decreases the total radiation doses and improves image quality in chest CT scanning. It is valuable and promising in chest CT scan.