Häggström Ida, Schmidtlein C Ross, Karlsson Mikael, Larsson Anne
Department of Radiation Sciences, Umeå University, Umeå 90187, Sweden.
Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York 10065.
Med Phys. 2014 Nov;41(11):111907. doi: 10.1118/1.4897610.
The aim of this study was to investigate the effect of scatter and its correction on kinetic parameters in dynamic brain positron emission tomography (PET) tumor imaging. The 2-tissue compartment model was used, and two different reconstruction methods and two scatter correction (SC) schemes were investigated.
The gate Monte Carlo (MC) software was used to perform 2 × 15 full PET scan simulations of a voxelized head phantom with inserted tumor regions. The two sets of kinetic parameters of all tissues were chosen to represent the 2-tissue compartment model for the tracer 3'-deoxy-3'-((18)F)fluorothymidine (FLT), and were denoted FLT1 and FLT2. PET data were reconstructed with both 3D filtered back-projection with reprojection (3DRP) and 3D ordered-subset expectation maximization (OSEM). Images including true coincidences with attenuation correction (AC) and true+scattered coincidences with AC and with and without one of two applied SC schemes were reconstructed. Kinetic parameters were estimated by weighted nonlinear least squares fitting of image derived time-activity curves. Calculated parameters were compared to the true input to the MC simulations.
The relative parameter biases for scatter-eliminated data were 15%, 16%, 4%, 30%, 9%, and 7% (FLT1) and 13%, 6%, 1%, 46%, 12%, and 8% (FLT2) for K1, k2, k3, k4, Va, and Ki, respectively. As expected, SC was essential for most parameters since omitting it increased biases by 10 percentage points on average. SC was not found necessary for the estimation of Ki and k3, however. There was no significant difference in parameter biases between the two investigated SC schemes or from parameter biases from scatter-eliminated PET data. Furthermore, neither 3DRP nor OSEM yielded the smallest parameter biases consistently although there was a slight favor for 3DRP which produced less biased k3 and Ki estimates while OSEM resulted in a less biased Va. The uncertainty in OSEM parameters was about 26% (FLT1) and 12% (FLT2) larger than for 3DRP although identical postfilters were applied.
SC was important for good parameter estimations. Both investigated SC schemes performed equally well on average and properly corrected for the scattered radiation, without introducing further bias. Furthermore, 3DRP was slightly favorable over OSEM in terms of kinetic parameter biases and SDs.
本研究旨在探讨散射及其校正对动态脑正电子发射断层扫描（PET）肿瘤成像中动力学参数的影响。采用双组织房室模型，并研究了两种不同的重建方法和两种散射校正（SC）方案。
使用门控蒙特卡罗（MC）软件对插入肿瘤区域的体素化头部模型进行2×15次全PET扫描模拟。选择所有组织的两组动力学参数来代表示踪剂3'-脱氧-3'-（（18）F）氟胸苷（FLT）的双组织房室模型，分别记为FLT1和FLT2。PET数据采用带重投影的三维滤波反投影（3DRP）和三维有序子集期望最大化（OSEM）进行重建。重建了包括经衰减校正（AC）的真符合事件以及经AC且应用两种SC方案之一或未应用该方案的真+散射符合事件的图像。通过对图像导出的时间-活度曲线进行加权非线性最小二乘拟合来估计动力学参数。将计算得到的参数与MC模拟的真实输入进行比较。
对于K1、k2、k3、k4、Va和Ki，散射消除后数据的相对参数偏差分别为15%、16%、4%、30%、9%和7%（FLT1）以及13%、6%、1%、46%、12%和8%（FLT2）。正如预期的那样，SC对于大多数参数至关重要，因为省略它会使偏差平均增加10个百分点。然而，发现SC对于Ki和k3的估计并非必要。两种研究的SC方案之间的参数偏差或与散射消除后的PET数据的参数偏差没有显著差异。此外，虽然3DRP对k3和Ki的估计偏差较小，而OSEM对Va的估计偏差较小，但3DRP和OSEM都没有始终产生最小的参数偏差。尽管应用了相同的后置滤波器，但OSEM参数的不确定性比3DRP大约26%（FLT1）和12%（FLT2）。
SC对于良好的参数估计很重要。两种研究的SC方案平均表现同样良好，并且对散射辐射进行了适当校正，没有引入进一步的偏差。此外，就动力学参数偏差和标准差而言，3DRP比OSEM略占优势。
