重建算法对CT图像空间和密度分辨率的影响

Study on the Influence of Reconstruction Algorithm on Spatial Resolution and Density Resolution of CT Images

目的:探讨重建算法对CT图像空间分辨率和密度分辨率的影响。方法:以Catphan500为检测载体,行不同(5~50mGy)容积CT剂量指数(CTDIvol)CT扫描,分别采用滤波反投影(FBP)算法、迭代重建(SAFIRE)算法(5个等级)、像素闪烁(PS)算法(9个等级)进行图像重建,观察并记录其空间分辨率和密度分辨率测试结果。结果:CTDIvol为50mGy时,各算法重建图像密度分辨率相同,FBP和各PS等级算法的空间分辨率测试结果为7.5lp/cm,高于各SAFIRE等级算法的7.0lp/cm(P<0.05);随CTDIvol的降低,各算法重建图像密度分辨率均快速降低,FBP算法的空间分辨率轻微降低(从7.5lp/cm降至7.0lp/cm),SAFIRE-3算法的空间分辨率稳定为7.0lp/cm,PS-5算法的空间分辨率先逐渐递减,至30mGy时,稳定在7.0lp/cm。结论:CTDIvol为50mGy时,各算法重建图像密度分辨率相同,FBP和PS系列算法重建图像空间分辨率可达7.5lp/cm,高于SAFIRE系列算法的7.0lp/cm(P<0.05),而CTDIvol的降低会导致图像密度分辨率快速降低,因此应合理使用低剂量扫描。

Purpose:To investigate the influence of reconstruction algorithms on the density resolution and spatial resolution of CT images.Methods:CTP 515 module and CTP 528 module of Cattphan 500 were used as detection carrier,CT scanning was done under different(5-50 mGy)volume CT dose index(CTDIvol).Filtered back projection(FBP),five levels of sinogram affirmed iterative reconstruction(SAFIRE)and nine levels of pixel shine(PS)were used to reconstruct the original data,and the density resolution and spatial resolution were observed and recorded.Results:When the CTDIvol was 50 mGy,the density resolution of the images reconstructed with different algorithms was the same,the spatial resolution of FBP and PS grade algorithms was 7.5 lp/cm,which was higher than that of SAFIRE grade 3(SAFIRE-3)algorithms(P<0.05).With the decrease of CTDIvol,the density resolution of the image reconstructed with any algorithm decreased rapidly,the spatial resolution of FBP algorithm decreased slightly(from 7.5 lp/cm to 7.0 lp/cm),the spatial resolution of SAFIRE-3 algorithm was stable at 7.0 lp/cm,the spatial resolution of PS grade 5(PS-5)algorithm decreased gradually at first and was stable at 7.0 lp/cm when it reached 30 mGy.Conclusion:When the dose index is 50 mGy,the density resolution of the reconstructed images of each algorithm are the same,the spatial resolution of the FBP and PS series algorithms can reach 7.5 lp/cm,higher than the 7.0 lp/cm of the SAFIRE series algorithms(P<0.05),and the decrease of CTDIvol will lead to the rapid decrease of image density resolution,so low dose scanning should be used reasonably.