64层容积CT数字减影血管造影扫描参数优化的实验研究

Optimization of scanning parameters for 64-slice volume CT digital subtraction angiography

目的:探讨管电流(mA)、管电压(kV)、层厚及螺距变化对64层容积CT数字减影血管造影(Volume computed tomograp hic digital subtraction angiography,VCTDSA)图像质量和辐射剂量的影响。方法:对颅骨标本采用VCTDSA扫描方法进行扫描,不同mA(100、85、75、65、50、25、10mA)、kV(两次扫描同步变化140、120、100、80kV;不同步变化120～140、100～140、80～140、100～120、80～120、80～100 kV)、层厚(0.625、1.25、2.5、3.75、5 mm)和螺距(0.531、0.969)的变化组合进行扫描,用Add/Sub软件进行减影,测量减影后全图CT值反映图像噪声,减影后图像行3D容积重建(3D Volume rendering,3D VR)评价减影图像质量。结果:变化mA、同步与非同步变化kV、变化层厚和同步变化螺距减影后图像质量均为Ⅰ级(100%),非同步变化螺距减影后图像质量为Ⅲ级(100%)。随mA、kV、层厚降低和螺距增大,减影后全图CT值增大,图像噪声增加而图像质量降低。非同步变化kV的双能量减影,随kV的增加,减影后全图CT值降低,图像噪声降低而图像质量提高。结论:应用双能量、厚层采集薄层重建、降低毫安和增加螺距,不仅能保证VCTDSA的图像质量,同时可降低X线辐射剂量。

Objective：To investigate the influence of scanning parameters （including mA, kV,sliee thickness and pitch） on image quality and radiation dose of volume computed tomographic digital subtraction angiography （VCTDSA）. Methods ： VCTDSA were performed on a skull specimen. Scans were obtained with different scanning parameters, including current of 100,85,75,65,50,25 and 10 mA, synchronic voltage modification of 140,120,100 and 80 k V, non-synchronic voltage modification of 120-140,100-140,80-140, 100-120, 80-120 and 80-100 k V, slice thickness of 0.625,1.25,2.5,3.75 and 5 mm, and pitch of 0.531, 0.969. CT numbers of the overall view were measured on subtraction images obtained from Add/Sub software. The image quality of subtraction images were analyzed, which were reformatted and displayed with 3D volume rendering（ 3D VR）. Results：Except subtracted image qualitys were evaluated grade Ⅲ （ 100% ） with non-synchronic pitch, other subtracted image qualitys were evaluated grade Ⅰ （ 100% ） undergoing different scanning parameters （mA, kV, slice thickness and synchronic pitch ）.With the decrease of mA,kV, slice thickness and the increase of pitch, CT numbers and imaging noise increased, and imaging quality after subtraction decreased. Image quality was improved and noise was reduced by dual energy subtraction. With the increase of kV, CT numbers increased. Conclusion： Image quality was improved and radiation dose was reduced by dual energy subtraction technique, thick collection and reconstruction in thin slice, decreasing mA and increasing pitch.