SPECT/CT活度定量中校准体模和重建方法的选择

Selection of Calibration Phantom and Reconstruction Method for SPECT/CT Activity Quantification

本文探讨了SPECT/CT校准体模和重建方法的选择,以用于临床SPECT/CT的准确活度定量。分别对活度已知的点源、大圆柱、小圆柱3种校准体模进行SPECT/CT扫描,然后对每个断层数据依次采用4种重建方法(FBP、OSEM、OSEM+AC、OSEM+AC+SC)进行重建,并据此计算校准因子。将小圆柱作为活度定量的对象进行定量误差计算。OSEM+AC和OSEM+AC+SC的平均相对定量误差均小于10%,FBP和OSEM的平均相对定量误差均大于20%。OSEM+AC的平均相对定量误差在采用小圆柱做校准体模时与OSEM+AC+SC无显著差异,而在采用大圆柱和点源时,分别较OSEM+AC+SC的小3.38%和6.48%(P<0.05)。3种体模的对比中,采用OSEM+AC时差异不显著,采用其他重建方法时差异显著。采用OSEM+AC+SC时,小圆柱作校准体模的定量误差较大圆柱和点源的结果分别小3.92%和6.42%(P<0.05)。结果表明,基于CT和迭代算法的衰减校正可有效提升活度定量准确性,但散射校正的效果不佳;校准体模应尽可能与目标定量对象相似。合理选择校准体模和重建方法,可有效提升SPECT/CT的活度定量准确性。

To optimize phantom and reconstruction strategy for the best activity quantitative performance of clinical SPECT/CT,three kinds of phantoms（point,small cylin-der and big cylinder）and four methods（FBP,OSEM,OSEM＋AC and OSEM＋AC＋SC）were employed to calculate calibration factor respectively,which was then used to reconstructed activity of a small cylinder.The relative errors were calculated by comparing these reconstructed activities with the measured ones from a dose calibrator.The relative quantification errors of OSEM＋AC and OSEM＋AC＋SC are both less than10%,while those of FBP and OSEM are greater than 20%.When using the big cylinder or the point phantom as calibration phantom,OSEM＋AC outperforms OSEM＋AC＋SC on quantification accuracy of about 3.38% or 6.48%（P0.05）respectively.The small cylinder phantom,with the smallest quantification error of less than 2%,was found to be the best option.Specifically in using OSEM＋AC＋SC,difference of mean relative quantification errors between the small cylinder phantom and the big one（or the point one）is 3.92%（or 6.42%,P0.05）.The activity quantification accuracy can be greatly improved using OSEM＋AC.However,this is not the case for scatter correction,which may even lead to larger errors.The calibration phantom should be as similar as the object to be quantified for better results.Finally,the proper selection of calibration phantoms and reconstruction methods can effectively reduce the activity quantification error of SPECT/CT.