Gustafsson Johan, Larsson Erik, Ljungberg Michael, Sjögreen Gleisner Katarina
Medical Radiation Physics, Lund, Lund University, Lund, Sweden.
Radiation Physics, Skåne University Hospital, Lund, Sweden.
EJNMMI Phys. 2024 Jul 15;11(1):62. doi: 10.1186/s40658-024-00667-7.
The aim was to investigate the noise and bias properties of quantitative Lu-SPECT with respect to the number of projection angles, and the number of subsets and iterations in the OS-EM reconstruction, for different total acquisition times.
Experimental SPECT acquisition of six spheres in a NEMA body phantom filled with Lu was performed, using medium-energy collimators and 120 projections with 180 s per projection. Bootstrapping was applied to generate data sets representing acquisitions with 20 to 120 projections for 10 min, 20 min, and 40 min, with 32 noise realizations per setting. Monte Carlo simulations were performed of Lu-DOTA-TATE in an anthropomorphic computer phantom with three tumours (2.8 mL to 40.0 mL). Projections representing 24 h and 168 h post administration were simulated, each with 32 noise realizations. Images were reconstructed using OS-EM with compensation for attenuation, scatter, and distance-dependent resolution. The number of subsets and iterations were varied within a constrained range of the product number of iterations number of projections . Volumes-of-interest were defined following the physical size of the spheres and tumours, the mean activity-concentrations estimated, and the absolute mean relative error and coefficient of variation (CV) over noise realizations calculated. Pareto fronts were established by analysis of CV versus mean relative error.
Points at the Pareto fronts with low CV and high mean error resulted from using a low number of subsets, whilst points at the Pareto fronts associated with high CV but low mean error resulted from reconstructions with a high number of subsets. The number of projection angles had limited impact.
For accurate estimation of the Lu activity-concentration from SPECT images, the number of projection angles has limited importance, whilst the total acquisition time and the number of subsets and iterations are parameters of importance.
目的是研究定量镥单光子发射计算机断层扫描（Lu-SPECT）在不同总采集时间下，关于投影角度数量、有序子集期望最大化（OS-EM）重建中的子集数量和迭代次数的噪声和偏差特性。
使用中能准直器，对填充有镥的NEMA体模中的六个球体进行实验性SPECT采集，每个投影180秒，共120个投影。采用自助法生成数据集，代表10分钟、20分钟和40分钟采集时间下20至120个投影的采集情况，每种设置有32个噪声实现。在具有三个肿瘤（2.8毫升至40.0毫升）的人体计算机体模中对Lu-DOTA-TATE进行蒙特卡罗模拟。模拟给药后24小时和168小时的投影，每种情况有32个噪声实现。使用OS-EM对图像进行重建，并对衰减、散射和距离依赖性分辨率进行补偿。子集数量和迭代次数在迭代次数×投影数量的乘积的受限范围内变化。根据球体和肿瘤的物理尺寸定义感兴趣体积，估计平均活度浓度，并计算噪声实现的绝对平均相对误差和变异系数（CV）。通过分析CV与平均相对误差建立帕累托前沿。
帕累托前沿上CV低但平均误差高的点是由于使用了少量子集，而帕累托前沿上CV高但平均误差低的点是由于使用大量子集进行重建。投影角度数量的影响有限。
为了从SPECT图像中准确估计镥活度浓度，投影角度数量的重要性有限，而总采集时间以及子集数量和迭代次数是重要参数。
