扫描方式对64层螺旋CT头颅CTA图像质量和辐射剂量影响的研究

目的：探讨64层螺旋CT扫描方式对头颅CTA图像质量和辐射剂量的影响。方法：采用GE Lightspeed VCT对100例需要行头颅CTA检查的患者进行对比研究，50例行螺旋扫描，另50例行轴层扫描。两组数据经过VR、MIP、去骨VR和多平面重组等方法后处理，然后由3组医师通过5分评价法对CTA图像质量进行主观评价，取其均值纳入统计学分析；记录每组扫描的容积剂量指数（CTDIvol）和剂量长度乘积（DLP）。对两组数据进行两独立样本t检验。结果：轴向扫描图像质量评分是（4．66±0．42）分、螺旋扫描CTA的成像质量评分（4．67±0．38）分；两组数据差异无统计学意义（P〉0．05）。轴向扫描、螺旋扫描的CTDIvol分别是45．71和54．18mGy；DLP分别是731．43和954．68mGy·cm。两组间差异有统计学意义（P〈0．05），轴层扫描方式辐射剂量更低。结论：64层CT头颅CTA轴扫可以显著降低辐射剂量而不降低图像质量，在临床运用中值得关注。

Comparison study of image quality and radiation dose between helical and axial CT angiography of the head with 64-slice helical CT

Objective： To compare the difference in image quality and radiation dose between helical and axial CT angiography of the head with 64-slices helical CT. Methods： 100 patients with suspected or confirmed cerehrovascuiar disease in our hospital,were divided into two groups to accept CTA examination ：helical scanning group （50 cases） and axial scan- ning group （50 cases）. Except the parameter of scanning method,each group was examined with the same scan parameters and equipment. 80ml contrast medium was injected （via a cubital vein） by 4.3ml/s and followed by 35ml normal sodium at the same speed. The cerebral vessels were imaged by these postprocessing methods：maximum intensity projection （MIP） volume rendering （VR）,and ＂Auto Select＂ technique. Three group of doctors evaluated the image quality by means of 5- point scoring subjective evaluation. The radiation dose report was auto-generated, the average value of volume CT dose index （CTDIvol） and dose length product （DLP） were taken into the sheet. All the data were processed by SPSS 13.0 and t test of independent sampler was used. Result：The image quality score of helical CTA was 4.67±0.38 and the axial was 4.66±0.42,there was no significant difference in image quality （P〉0.05）. Two kinds of scan both met the demand of diagnosis. The CTDIvol of axial CTA and helical CTA was 45.71and 54. 18mGy,the DLP was 731.43 and 954.68mGy-cm respec- tively,the difference of CTDIvol, DLP between two scan type was significant （P〈 0.05）. As compared with the helical group,the radiation dose of axial group was significantly decreased, including the DLP reduced by 34%, the CTDIvol re- duced by 16%. Conclusion.. Axial scaning leaded to significant reduction of effective dose at head CTA with 64-slice CT, without evident loss of image quality.