多层螺旋CT扫描方式准直与重建层厚对噪声的影响

目的探讨多层螺旋CT不同的扫描方式、准直宽度、重建层厚对图像噪声(质量)影响。方法使用Philips Brilliance 16层螺旋CT机与随机体模,用轴扫和螺旋扫描2种方式,固定管电流(200 mAs)与管电压(120kV)等其他扫描参数,分别以不同准直对头模部分扫描,不同层厚重建,测量CT值噪声(SD)并统计学处理与客观评价。结果①螺旋扫描与轴扫图像SD的差异有统计学意义(P<0.05),螺旋扫描噪声高;②不同准直扫描,图像SD差异无统计意义(P>0.05);③不同层厚,图像SD值随层厚增大而减低,统计学分析,6 mm与4.5、9 mm,12 mm与9、18mm图像SD值差异无统计意义(P>0.05),0.75、1.5、3、4.5 mm间差异均有统计学意义(P<0.01)。结论使用轴扫,图像噪声低,可以一定程度提高图像质量;扫描时应采用较大准直宽度扫描,增大单位时间覆盖面积以降低辐射剂量;根据诊断任务,选取适当重建层厚的观察图像,5 mm是常规观察图像合理层厚。

Influence on the noise of different scanning mode, collimation and reconstruction in multi-slice CTMO

Objective To explore the image noise(quality) of different scanning,collimation widths and recons-truction slice thickness in Multi-slice CT.Methods Using the Philips Brilliance 16 slice CT machine and the random phantom,there were 2 way of axial scan and helical scan.Then scaning respectively different reconstruction slice thickness in the alignment head scan mode,fixed the scanning parameters(200 mAs,120 kV).The CT value(SD) was measured,analyzed statistically and evaluated.Results Helical scanning noise was significantly higher than axial scan noise(P<0.05).The image SD of different collimation scanning had no difference(P>0.05).The image SD value reduced with the thickmess increasing.There was no difference(4.5 mm,9 mm contrast 6 mm;9 mm,18 mm contrast 12 mm)(P>0.05).There was signifficant difference among 0.75 mm,1.5 mm,3 mm,4.5 mm(P<0.01).Conclusion Use axis sweep,low noise images can improve image quanlity to a certain extent;Scan collimation width should be used for a larger scan,increasing the coverage area per unit time to reduce the radiation dose;According to the diagnostic task,it should be selected of the appropriate thickness of the observed image reconstruction,5 mm thickness is normal and reasonable observation image.