The Application Of Auto-mA Low-kV CT Scanning On Head And Neck CT Angiography

Objective:To evaluate the effect of auto-mA low-kV CT scanning to image quality and radiation dose for the head and neck CT angiography.Materials and Methods:This prospective study was performed for 40 patients needed head and neck CTA (2008.8-2009.2). Patients were randomly divided into four groups:group I kV=100, NI=20; groupâ…¡:kV=120, NI=20; groupâ…¢:kV=100, NI=10; groupIV kV=120, NI=10. Cross-section images were obtained with 64 mutislice spiral CT scanner(GE LightSpeed VCT XT). The other parameters include: slice thickness 0.625mm, pitch 0.984,0.4s/rot, FOV 22cm, matrix 512*512, standard algorithm. Images were all transmitted to off-line workstation (GE AW4.4) and volume rendering (VR), multiplanar reformat (MPR) were reformatted for further scoring. Quantitative and qualitative analysis of image were performed, and radiation dose was recorded. The parameters of quanlitative analysis included intraluminal attenuation of artery (CT value), image noise, background signal, signal-to-noise ration (SNR), contrast-to-noise rate (CNR). The quanlitative analysis of image quality used 5-point grade for cross-section images (1, poor; 2, acceptted; 3, satisfied; 4, good; 5, excellent) and 3-point grade for VR and MPR images (1, poor; 2, satisfied; 3, excellent).Radiation dose included CT dose index-volume (CTDIvol), dose length product (DLP), and effective dose (ED). The methods of statistics analysis were ANOVA and t test, and P<0.05 represented the significant difference.Results:The differences between CT value, noise and background signal were significant. In the same NI, with decreasement of kV, CT value, noise, and background signal were all increased. However, SNR and CNR had no significant difference, and the decreasement of kV had no significant effect on them. In the same NI, there was no significant difference among the image quality of four groups, including VR and MPR. In the same kV, the image quality of two NI=10 groups is obvious bettter than the other two NI=20 groups.Conclusions:Auto-mA low-dose CT scanning can reduce radiation dose significantly, meanwhile ensure the image quality. It is highly suggested to use lower radiation dose parameters in clinical settings. kV=100 and NI=20 scan protocol can guarantee the imaging quality of diagnostic purpose.