球管焦点选择对多排螺旋CT后颅凹成像图像质量的影响

目的:探讨球管大小焦点的选择对多排螺旋CT后颅凹成像图像质量的影响。材料和方法:采用Light Speed VCT(美国GE公司,探测器64×0.625mm,焦点大小0.6mm×0.7mm和0.9mm×0.9mm)多排螺旋CT,在保证其他扫描参数一致基础上,分别使用球管大、小焦点对20例志愿者后颅凹相同层面进行轴位扫描,所得图像调成相同窗宽、窗位后使用Kodak 8700干式激光打印机打印输出。由两位5年以上工作经验放射科医师分别对后颅凹层面的图像质量评价打分。阅片结果采用SPSS 11.5软件包进行组间Kappa检验及组内x²检验。结果:两位医师对于后颅凹层面的图像质量评价结果具有一致性(Kappa值=0.57),使用小焦点扫描颅底图像质量优于大焦点扫描(P<0.05)。结论:多排螺旋CT使用小焦点扫描可以改善图像质量。

Effect of Focal Spot Size on Image Quality in 64-Row MDCT Brain Imaging

Objective： To evaluate the effect of different focal spot sizes on image quality in 64-row MDCT brain imaging. Method： Plain cranial axial CT scans were performed on twenty healthy volunteers with GE LightSpeed VCT （64×0.625 mm detectors, small focal spot size 0.6 mm×0.7 mm, large focal spot size 0.9 mm×0.9 mm）. Informed consents were obtained in all volunteers. Axial scans across the posterior cranial fossa were performed with different focal spots on all subjects, with the other parameters not changed. The images were printed at the same window setting with Kodak Dryview 8700 laser imager and reviewed by two radiologists to rate the artifacts of bony structures at posterior cranial fossa. The results were analyzed with SPSS 11.5 for Kappa test and intragroup Chi-square test. Results： The two radiologists were in accordance with the rating of the artifacts at posterior cranial fossa （Kappa = 0.57）. Less artifacts were observed at posterior cranial fossa with small focal spots than with large focal spots （P 〈 0.05）. Conclusion： Artifacts of cranial base can be reduced by using small focal spots on 64-row MDCT brain scan. Using small focal spot in clinical examination, better image quality can be achieved in brain CT scan.