Häggström Ida, Axelsson Jan, Schmidtlein Charles Ross, Karlsson Mikael, Garpebring Anders, Johansson Lennart, Sörensen Jens, Larsson Anne
Department of Radiation Sciences, Umeå University, Umeå, Sweden
Department of Radiation Sciences, Umeå University, Umeå, Sweden.
J Nucl Med Technol. 2015 Mar;43(1):53-60. doi: 10.2967/jnmt.114.141754. Epub 2015 Jan 22.
Compartmental modeling of dynamic PET data enables quantification of tracer kinetics in vivo, through the calculated model parameters. In this study, we aimed to investigate the effect of early frame sampling and reconstruction method on pharmacokinetic parameters obtained from a 2-tissue model, in terms of bias and uncertainty (SD).
The GATE Monte Carlo software was used to simulate 2 × 15 dynamic 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) brain PET studies, typical in terms of noise level and kinetic parameters. The data were reconstructed by both 3-dimensional (3D) filtered backprojection with reprojection (3DRP) and 3D ordered-subset expectation maximization (OSEM) into 6 dynamic image sets with different early frame durations of 1, 2, 4, 6, 10, and 15 s. Bias and SD were evaluated for fitted parameter estimates, calculated from regions of interest.
The 2-tissue-model parameter estimates K1, k2, and fraction of arterial blood in tissue depended on early frame sampling, and a sampling of 6-15 s generally minimized bias and SD. The shortest sampling of 1 s yielded a 25% and 42% larger bias than the other schemes, for 3DRP and OSEM, respectively, and a parameter uncertainty that was 10%-70% higher. The schemes from 4 to 15 s were generally not significantly different in regards to bias and SD. Typically, the reconstruction method 3DRP yielded less frame-sampling dependence and less uncertain results, compared with OSEM, but was on average more biased.
Of the 6 sampling schemes investigated in this study, an early frame duration of 6-15 s generally kept both bias and uncertainty to a minimum, for both 3DRP and OSEM reconstructions. Very-short frames of 1 s should be avoided because they typically resulted in the largest parameter bias and uncertainty. Furthermore, 3DRP may be preferred over OSEM for short frames with poor statistics.
动态正电子发射断层扫描（PET）数据的房室模型能够通过计算模型参数对体内示踪剂动力学进行定量分析。在本研究中，我们旨在从偏差和不确定性（标准差）方面，研究早期帧采样和重建方法对从双组织模型获得的药代动力学参数的影响。
使用GATE蒙特卡罗软件模拟2×15次动态3'-脱氧-3'-(18)F-氟胸苷（(18)F-FLT）脑部PET研究，这些研究在噪声水平和动力学参数方面具有典型性。数据通过三维（3D）带重投影的滤波反投影（3DRP）和3D有序子集期望最大化（OSEM）重建为6组具有不同早期帧持续时间（1、2、4、6、10和15秒）的动态图像集。从感兴趣区域计算拟合参数估计值的偏差和标准差进行评估。
双组织模型参数估计值K1、k2和组织中动脉血分数取决于早期帧采样，6 - 15秒的采样通常使偏差和标准差最小化。对于3DRP和OSEM，最短的1秒采样分别比其他方案产生大25%和42%的偏差，且参数不确定性高10% - 70%。4至15秒的方案在偏差和标准差方面通常无显著差异。通常，与OSEM相比，重建方法3DRP产生的帧采样依赖性较小且结果不确定性较小，但平均偏差较大。
在本研究中研究的6种采样方案中，对于3DRP和OSEM重建，6 - 15秒的早期帧持续时间通常使偏差和不确定性都降至最低。应避免1秒的极短帧，因为它们通常会导致最大的参数偏差和不确定性。此外，对于统计数据较差的短帧，3DRP可能比OSEM更可取。
