256层CT头部扫描iDose 4^(TM)重建图像空间分辨性能的模体实验

Spatial resolution investigation on iDose 4^(TM) with 256-slice CT in brain spiral scanning:A phantom study

目的探讨256层Brilliance iCT头部扫描时不同扫描条件下各重建级别iDose空间分辨性能的差异。方法采用256层Brilliance iCT和CT性能检测模体,获得头部扫描图像,以iDose和滤波反投影(FBP)两种方法进行重建,比较两种重建图像的调制传递函数(MTF)曲线之间的差异。结果①MTF曲线显示,同等辐射剂量条件下,相比FBP重建,iDose重建可提高1.75%~115.62%的空间分辨能力。②降低层厚会在一定程度上降低CT系统在xOy平面内的空间分辨能力。③层厚为0.9mm时,iDose(6)的图像重建性能最好,层厚为2.5mm时,iDose(5)的性能最好。④在保持千伏值、毫安秒及扫描层厚条件不变,螺距从0.203提高至0.391时空间分辨能力无显著差异。⑤保持毫安秒不变,同时改变管电流和扫描时间,使用iDose重建算法CT系统空间分辨能力无显著差异。结论 iDose在同等辐射剂量下能显著提高图像质量,一定程度上iDose重建图像的空间分辨力对螺距和管电流改变不敏感。为获得最佳图像质量,重建级别应与层厚相适应。

Objective To assess spatial resolution performance of various iDose reconstruction levels at Brilliance iCT 256 with brain scanning protocol under varied conditions. Methods CT images of brain were obtained using Brilliance iCT 256 and CT image quality phantom test. CT images were reconstructed using iDose 4TM and filter back projection （FBP）. Mod- ulation transfer function （MTF） of reconstructed CT images was calculated and compared. Results ①MTF of image with iDose was 1.75 %--115.62% greater than FBP at equal radiation dose level.. ②SPatial resolution in x-O-y plane would de- crease at some extend when scanning slice depth decreases. ③For varied iDose levels, iDose （6） got the best MTF when slice depth was 0.9 mm, while iDose （5） gained the best MTF when slice depth was 2.5 ram. ONo obvious difference of MTF was found when pitch varied from 0. 203 to 0. 391 while voltage, mill-ample multiple second and slice depth constant kept the same. ④No obvious difference of MTF was found at the same mill-ample multiple second constant and different mill-ample and scanning time. Conclusion iDose can obviously increase spatial resolution at the same dose level, and spa- tial resolution of CT image with iDose reconstruction is not too much sensitive to pitch and lamp current to some extent. Reconstruction level should suit scanning depth in order to acquire best image quality.