OSEM和TVREM重建算法对全景PET短时采集图像质量的对比研究

Comparative study of OSEM and TVREM algorithms on image quality of total-body PET with short acquisition

目的探讨比较有序子集最大期望值迭代算法(OSEM)与正则化迭代法(TVREM)对全景PET短时扫描图像质量的影响,并确定短时PET扫描获得最佳图像质量的最优正则化系数(β值)。方法通过模体试验的背景变异性(BV)、背景变异系数(COV)和小球活度恢复系数(CRC)评估不同时间下OSEM和TVREM(β=0.15~0.95)两种重建算法PET图像质量的影响。连续收集行18 F-FDG全景PET/CT检查的45例患者资料,采用与模体相同的算法序列进行重建。按照病变大小分为3组。比较各组的肝脏背景噪声、信噪比(SNR)、病变最大标准化摄取值(SUVmax)和靶本比(TBR)。行Kappa检验和Wilcoxon秩和检验分析数据。结果模体研究显示相同采集时间下TVREM的BV、COV均小于OSEM,热球的CRC均高于OSEM(除60 s~0.75,0.95),且随着β值的增加而降低。临床结果显示在相同时间下TVREM中背景噪声均低于OSEM(P<0.001),且随时间和β值的增加而减低,肝脏SNR随采集时间和β值的增加而增高。TVREM组病变SUVmax和TBR比OSEM增高(P<0.001),小于10 mm的病变SUVmax增高更明显(提升范围40.8%~54.9%)。2位医师对图像质量的诊断一致性较强(kappa值为0.729)。结论与OSEM相比,TVREM可以降低图像噪声、显著提高图像质量及病变的SUVmax,≤10 mm病变更显著。对于全景PET短时采集,推荐使用T=60 s,β=0.35~0.55。

Objective To compare the effects of the ordered subset expectation maximum(OSEM)and total variation regularized expectation maximization(TVREM)on the image quality of total-body PET with short acquisition,and to determine the optimal regularization factor(βvalue)for obtaining the best image quality for short-time PET scans.Methods The BV,COV,and CRC were evaluated between different reconstruction algorithms〔OSEM and TVREM(β=0.15~0.95)〕with different acquisition time in the phantom test.Forty-five patients who underwent total-body 18 F-FDG PET/CT were collected and the data were reconstructed using the same algorithmic sequence as the phantom study.All lesions were divided into 3 groups by longest axis diameter.The image noise,signal-to-noise ratio(SNR)of liver,maximum standardized uptake value(SUVmax),and target-to-background ratio(TBR)of lesions were compared among the groups.Kappa test and Wilcoxon rank sum test were performed.Results In phantom study,the BV and COV values of TVREM algorithm with the same acquisition time were smaller than those of OSEM algorithm,and the CRC of hot sphere was higher than that of OSEM(except 60s-0.75,0.95),and decreased with increasingβvalue.Clinical studies showed that image noise was lower in TVREM than OSEM at the same time(P<0.001)and decreased with increasing time andβvalue.Liver SNR increased with increasing acquisition time andβvalue.Lesion SUVmax and TBR were higher in the TVREM group than OSEM(P<0.001),and SUVmax increased more significantly in lesions smaller than 10 mm(increased from 40.8%to 54.9%).There was strong diagnostic agreement between the 2 physicians for image quality(kappa value of 0.729).Conclusion Compared with OSEM,TVREM can reduce image noise,and significantly improve image quality and SUVmax of lesions,especially for lesions less than 10 mm.For total-body PET with short-time acquisition,the combination of T=60 s andβ=0.35~0.55 are recommended.