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目的探讨多层螺旋CT的扫描参数螺距的变化对辐射剂量的影响。方法对于LightSpeed16层螺旋CT和Sensation16层和64层螺旋CT,将长杆电离室分别置于16mm剂量体模的5个孔中,选用不同的螺距进行扫描并测量辐射剂量。结果3种机型轴扫和螺旋扫描的CTDIvol分别为:(1)对于lightSpeed16层螺旋CT,在轴扫及螺距分别为0·562、0·938,1·75时,分别等于28·9、51·4、30·8,16·5;(2)对于Sensation16层螺旋CT,在轴扫及螺距分别为0·5,1、1·5时,分别等于41·2、40·3、41·5,43·2;(3)对于Sensation64层螺旋CT,在轴扫及螺距分别为0·5,1·1·5时,分别等于41·2、40·3、41·5,43·2。结论对于LightSpeed16层螺旋CT,随着螺距的增加,辐射剂量降低,为保持恒定的图像质量,必须增大mAs作为补偿;Sensation16层和64层螺旋CT,因采用了mAs自动调整技术,在不同的螺距下辐射剂量相同,图像质量稳定。日常操作中当螺距改变时,应根据不同机型来确定调整管电流的方法。
Objective To investigate the effect of the variation of the pitch of scanning parameters on the radiation dose of multi-slice spiral CT. Methods For the LightSpeed 16-slice spiral CT and Sensation 16-slice and 64-slice spiral CT, the long pole ionization chambers were placed in 5 holes of a 16 mm dose phantom, respectively, with different pitch to scan and measure the radiation dose. Results CTDIvol of axial scan and helical scan of the three models were as follows: (1) For lightSpeed 16-slice CT, the axial sweep and pitch were 0 · 562, 0 · 938 and 1 · 75, respectively, 51 · 4, 30 · 8, 16 · 5; (2) For Sensation 16-slice CT, when the axial sweep and the pitch are 0 · 5, 1, 1 · 5 respectively, they are equal to 41 · 2, 40 · 3, · 5,43 · 2; (3) For the Sensation 64-slice spiral CT, when the axial sweep and the pitch are 0 · 5 and 1 · 1 · 5 respectively, they are equal to 41 · 2, 40 · 3, 41 · 5 and 43 · 2. Conclusion For LightSpeed 16-slice spiral CT, with the increase of the pitch, the radiation dose is reduced. In order to maintain a constant image quality, mAs must be increased as a compensation. Sensation16 layer and 64-slice spiral CT, due to the automatic adjustment technology of mAs, Pitch under the same radiation dose, image quality and stability. In daily operation when the pitch changes, should be based on different models to determine the method of adjusting the tube current.