目的 探讨三维有序子集最大期望值法(3D-OSEM)、二维有序子集最大期望值法(2D-OSEM)、滤波反投影(FBP)重建图像及OSEM迭代次数和子集数对SPECT/CT定量计算结果的影响.方法 分别对Jaszczak圆筒模型、NEMA/IEC体模进行SPECT/CT断层显像,并进行CT衰减校正和散射校正以及3D-OSEM图像重建.根据Jaszczak圆筒模型重建图像获得特定采集及重建条件下的系统容积灵敏度(cpm/kBq),计算IEC体模内不同大小放射性热区的绝对放射性活度(kBq/ml;绝对定量值),并与真实活度值进行比较,计算定量误差.改变图像重建算法(2D-OSEM、FBP)和OS-EM重建参数(迭代次数和子集数)对IEC体模进行图像重建,比较不同重建算法及OSEM迭代次数和子集数对定量误差的影响.结果 采用3D-OSEM、2D-OSEM、FBP重建图像时,各球体定量误差均随球体容积的减小而明显增大(r=-0.831、-0.831、-0.826,P均＜0.05).3种重建算法间不同容积球体定量误差差异有统计学意义(F=8.850,P＜0.05),其中,3D-OSEM小于2D-OSEM重建(P＜0.05),2D-OSEM小于FBP重建(P＜0.05).各不同容积球体定量误差均随迭代次数增加而减小(r=-0.721、-0.681、-0.691、-0.711、-0.845、-0.893,P均＜0.05),随子集数的增加而减小(r=-0.670、-0.694、-0.717、-0.852、-0.956、-0.998,P均＜0.05).结论 基于CT衰减校正和散射校正的3D-OSEM重建定量精确性明显优于2D-OSEM、FBP重建,选择合适的OSEM重建参数有利于提高SPECT/CT定量精确性.%Objective To evaluate the impact of 3-dimensional ordered subset expectation maximization (3D-OSEM),2-dimensional ordered subset expectation maximization (2D-OSEM),filtered-back projection (FBP),and the number of OSEM iterations and subsets on quantitative results in SPECT/CT.Methods A Jaszczak cylindrical phantom and NEMA/IEC body phantom were performed in routine SPECT/CT using CT attenuation correction,scatter correction and 3D-OSEM reconstructed image.The system volume sensitivity (cpm/kBq) was acquired from the reconstructed image of Jaszczak phantom,and the absolute activity concentration (kBq/ml) of the hot sphere from IEC phantom was calculated and compared with true activity concentration,then quantitative error was calculated.With changing the reconstruction algorithm (2D-OSEM,FBP) and OSEM reconstruction parameters (number of iterations and subsets) to reconstruct the IEC phantom,the differences of quantitative results from different reconstruction algorithms and OSEM iterations and subsets were compared.Results When reconstructing images with 3D-OSEM,2D-OSEM and FBP,the quantitative error of each sphere increased with the decrease of the spherical volume (r=-0.831,-0.831,-0.826,all P＜0.05).The quantitative error of different volume spheres among three reconstruction algorithms was statistically significant (F=8.850,P＜0.05).Among them,the result of 3D-OSEM was less than that of 2D-OS EM (P＜0.05),and of 2D-OSEM was less than of FBP (P＜0.05).The quantitative error of different volume spheres decreased with the increasing of number of iterations (r=-0.721,-0.681,-0.691,-0.711,-0.845,-0.893,all P＜0.05) and decreased with the increase of number of subsets (r=-0.670,-0.694,-0.717,-0.852,-0.956,-0.998,all P＜0.05).Conclusion The quantitative accuracy of 3D-OSEM reconstruction based on CT attenuation correction and scattering correction is significantly better than that of 2D-OSEM and FBP.Choosing the appropriate OSEM reconstruction parameters is helpful to improve the quantification accuracy in SPECT/CT.
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