Objective To investigate the effects on image quality of volume computed tomographic digital subtraction angiography (VCTDSA) with synchronous and asynchronous scanning.Methods Vascular model which was closely attached to bony structures was scanned by 64slice spiral CT.① Helical scanning was performed without contrast medium injection for 20 times and the tube exposure time was 2.1 s, scanning intervals differently were 1.9 s, 3.9 s, 5.9 s, 7.9 s, 9.9 s, 11.9 s, 13.9 s, 15.9 s, 17.9 s, 19.9 s, 2.9 s, 11.9 s, 6.9 s, 8.9 s, 10.9 s, 3.0 s, 4.0 s, 5.0 s, 6.0 s, 7.0 s.②After contrast medium injection, the vascular model was scanned for 10 times using the same parameters as above, but the scanning intervals differently were 9.9 s, 11.9 s,13.9 s, 15.9 s, 17.9 s, 10.9 s, 12.9 s, 11.0 s, 12.0 s, 13.0 s.The resulting images were reformatted as 3D volume rendering (3D VR) and maximum intensity projection ( MIP) images.The quality of subtraction images was then analyzed.CT values of the overall view were measured on subtracted images and the differences of tube exposure angle were recorded.Results Subtracted images quality of VCTDSA was rated grade Ⅰ with synchronous scanning for 15 times before and after contrast medium injection,while with asynchronous scanning for 15 times, 2 times were grade Ⅰ , 12 times were grade n and 1 time was grade Ⅲ.In 20 times, the average CT value of subtracted images with asynchronous scans was higher than which with synchronous scans without contrast injection.The differences of tube exposure angle with synchronous scans were obviously less than which with asynchronous scans.Conclusion The position of tube can be well matched with synchronous scanning, so the image quality of VCTD SA is improved significantly.%目的 探讨同步与非同步扫描对64层容积CT数字减影血管造影(VCTDSA)图像质量的影响.方法 建立紧贴骨结构的血管模型,采用64层螺旋CT进行扫描:(1)未注射对比剂螺旋扫描20次,球管曝光时间为2.1 s,扫描间隔时间分别为1.9、3.9、5.9、7.9、9.9、11.9、13.9、15.9、17.9、19.9、2.9、4.9、6.9、8.9、10.9、3.0、4.0、5.0、6.0、7.0 s.(2)注射对比剂后螺旋扫描10次,扫描间隔时间分别为9.9、11.9、13.9、15.9、17.9、10.9、12.9、11.0、12.0、13.0 s,其余扫描参数同(1).减影后数据行3D容积再现(VR)及最大密度投影(MIP)图像重组,评价减影后图像质量、测量减影后全幅图像CT值、记录球管曝光角度差.结果 注射对比剂前、后同步扫描15次,减影后图像质量均为Ⅰ级,非同步扫描15次,减影后图像质量Ⅰ级2次、Ⅱ级12次、Ⅲ级1次;20次未注射对比剂减影后图像CT值比较,非同步扫描减影后图像CT值均数大于同步扫描;同步扫描的球管曝光角度差均数明显小于非同步扫描.结论 同步扫描保证球管曝光的起始位置相同,明显提高了VCTDSA减影后的图像质量.
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