OSEM重建的设置对于99mTcO_(4)^(-)SPECT/CT定量准确性的影响

Impact of OSEM Iterations and Subsets on Quantitative Accuracy of 99mTcO_(4)^(-)SPECT/CT

目的本研究通过分析有序子集最大期望值(Ordered-Subset Expectation Maximum,OSEM)迭代重建参数和99mTcO_(4)^(-)SPECT/CT定量准确性之间的关系,以优化SPECT图像重建参数设置。方法采用NEMA/IEC图像质量模型,6个热球和本底分别灌注126.54 KBq/mL和7.03 KBq/mL 99mTcO_(4)^(-)(热球-本底比为18:1),通过SPECT进行断层图像采集,并通过Q.Metrix软件对断层图像进行后处理和定量分析。所有断层图像采用OSEM算法进行重建(迭代次数分别为2、10、20、30、40、50、60和70;子集数分别为5、10、15、20和25)。通过计算热球靶区的平均恢复系数(Mean Recovery Coefficients,RCmean)评估不同重建参数设置的SPECT/CT定量准确性。结果所有热球的RCmean随着迭代次数的增加而增加,尤其对于13、17、22 mm热球变化明显,迭代50次后RC_(mean)达到平稳状态,当迭代次数由2增加到10时,RC_(mean)增加的幅度最大。但不同的子集数对于RC_(mean)无明显影响。曲线回归分析热球RC_(mean)值与热球体积之间存在非线性变化,函数关系为对数函数形式,预估曲线模型为y=0.167ln(x)+0.486,R^(2)=0.93(P<0.05)。结论在OSEM迭代次数方面,SPECT/CT图像的定量准确性随着迭代次数的递增而得到明显提升,尤其对于小病灶,当迭代50次时,可达到最大收敛。而子集数对定量准确性无明显影响。RC与热球体积之间存在确定对数函数关系,为不同大小病灶的99mTcO_(4)^(-)SPECT/CT定量参数的校正提供可靠的理论依据。

Objective In this study,the relationship between the iterative reconstruction parameters of Ordered Subset Maximum(OSEM)and the quantitative accuracy of 99mTcO_(4)^(-)SPECT/CT was analyzed to optimize the parameter setting of SPECT image reconstruction.Methods Using NEMA/IEC image quality model,six hot spheres and background were infused with 126.54 KBq/mL and 7.03 KBq/mL 99mTcO_(4)^(-)(hot spheres to background ratio was 18:1),respectively.SPECT was used for sectional image collection,and Q.Metrix software was used for post-processing and quantitative analysis of sectional images.OSEM algorithm was used to reconstruct all the fault images(i=2,10,20,30,40,50,60 and 70)and subsets(s=5,10,15,20 and 25).The mean recovery coefficients(RCmean)were calculated to evaluate the quantitation accuracy of SPECT/CT with different reconstruction parameter Settings.Results RC_(mean) of all hot spheres increased with the increase of iteration number,especially for 13 mm,17 mm and 22 mm hot spheres.After 50 iterations,RC_(mean) reached a plateau.When the number of iterations increased from 2 to 10,RCmean increased most obviously.However,different subsets had no significant effect on RCmean.The RC_(mean) value of the hot sphere and the volume of the hot sphere had nonlinear changes according to the curve regression analysis,and the function relationship was in the form of logarithmic function,and the logarithmic function of the estimated curve model is y=0.167ln(x)+0.486,R^(2)=0.93(P<0.05).Conclusion The quantitation accuracy of 99mTcO_(4)^(-)SPECT/CT was improved with increased of OSEM iteration numbers,especially for small spheres,the maximum convergence was achieved when the number of iterations was 50.The subsets number has no significant effect on the quantitative accuracy.There is a definite logarithmic function relationship between RCmean and sphere size,which provides a reliable theoretical basis for the calibration of quantitative parameters of 99mTCO_(4)^(-)SPECT/CT in different lesions.