基于自动管电流调制技术偏中心定位对胸部CT图像质量和辐射剂量的影响

Effect of off-center positioning based on ATCM technique on CT image quality and radiation dose on chest

目的:探讨自动管电流调制(ATCM)技术用于胸部CT扫描时的偏中心定位对图像质量及辐射剂量的影响。方法:应用GE Revolution 256排螺旋CT机采用ATCM技术对胸部仿真模体行CT扫描,通过调整检查床高度模拟实现偏中心情况。依据扫描定位方式将采用后前定位像扫描方法纳入后前定位像组,采用双定位像扫描方法纳入双定位像组,两组均以模体腋中线为中心,调整检查床高度,模拟模体在扫描野中的不同位置。每组分别在腋中线80 mm、60 mm、40 mm、20 mm、0 mm、-20 mm、-40 mm、-60 mm及-80 mm处扫描体模。两组均在相同的扫描参数件下扫描,记录其图像的容积CT剂量指数(CTDIvol)和剂量-长度-乘积(DLP)。测量并比较两组图像的客观噪声(SD),由2名具有5年及以上工作经验的放射科主治医生采用双盲法对磨玻璃密度结节(GGN)进行主观评分,取评分均值评价结果。结果:后前定位像组定位在偏中心-80 mm时的CTDIvol为4.56,与在偏中心0 mm比较增加了54.05%,偏中心80 mm时的CTDIvol为2.12,与在偏中心0 mm比较降低了28.38%。双定位像组定位在偏中心-80 mm时的CTDIvol为3.20,与在偏中心0 mm比较降低了3.61%,在偏中心80 mm时的CTDIvol为3.31,与偏中心0 mm比较降低了0.30%。两组不同偏中心位置扫描对GGN主观评分无统计学差异。结论:采用后前定位像扫描时,偏中心定位扫描对辐射剂量的影响较大,采用双定位像扫描时,偏中心定位扫描对辐射剂量无影响。在临床上对不能确定胸廓侧位中心时,应采用双定位像进行胸部CT扫描,可减少患者辐射剂量。

Objective:To investigate the effect of off-center positioning on image quality and radiation dose when automatic tube current modulation(ATCM)technique is used in computed tomography(CT)scanning on chest.Methods:A GE Revolution 256-row spiral CT machine was used to perform CT scan on a simulation phantom of chest by adopting ATCM technique,and the off-center situation was simulated by adjusting the height of the examination bed.The posterior-anterior localization image scanning method was adopted to enroll the posterior-anterior localization image group,and the dual-localization image scanned the dual-localization image group,and both groups were centered as the mid-axillary line of the body.The different positions of phantom in scan field were simulated through adjusted the height of the examination bed.The phantom of each group was scanned at 80 mm,60 mm,40 mm,20 mm,0 mm,-20 mm,-40 mm,-60 mm and-80 mm of the mid-axillary line.Both groups were scanned under the same scanning parameters,and the volume CT dose index(CTDIvol)and dose-length-product(DLP)were recorded for each group.The objective noise(SD)of the imageries of two groups were measured and compared,and two attending physicians with 5 years of work experiences of radiology department adopted respectively dual blind method to conduct subjective scoring for ground glass nodules(GGN),and the mean of scores was used to evaluate the results.Results:The CTDIvol value of the posterior-anterior localization image group was 4.56 when the off-center was-80 mm of the mid-axillary line,which increased 54.05%than that when the off-center was 0 mm.The CTDIvol value was 2.12 when the off-center was 80 mm,which decreased 28.38%than 0 mm of off-center.The CTDIvol value was 3.20 when the dual-localization image group was located at-80 mm of off-center,which decreased 3.61%than 0 mm of off-center.The CTDIvol value was 3.31 when the off-center was 80mm,which decreased 0.30%than that when off-center was 0mm.There was no statistically significant difference in subjective GGN scores between the two groups at different positions of off-center.Conclusion:Off-center positioning scan has greater effect on radiation dose when using posterior-anterior localization image scans,while the off-center positioning scan does not have effect on radiation dose when using dual localization image scan.The dual localization image should be adopted to perform CT scan on chest when the lateral center of the thorax cannot be determined in clinical practice,which can reduce the radiation dose of patients.