The world’s first 194-cm-long total-body PET/CT scanner (uEXPLORER) has been built by the EXPLORER Consortium to offer a transformative platform for human molecular imaging in clinical research and health care. Its total-body coverage and ultra-high sensitivity provide opportunities for more accurate tracer kinetic analysis in studies of physiology, biochemistry, and pharmacology. The objective of this study was to demonstrate the capability of total-body parametric imaging and to quantify the improvement in image quality and kinetic parameter estimation by direct and kernel reconstruction of the uEXPLORER data. Methods: We developed quantitative parametric image reconstruction methods for kinetic analysis and used them to analyze the first human dynamic total-body PET study. A healthy female subject was recruited, and a 1-h dynamic scan was acquired during and after an intravenous injection of 256 MBq of ¹⁸F-FDG. Dynamic data were reconstructed using a 3-dimensional time-of-flight list-mode ordered-subsets expectation maximization (OSEM) algorithm and a kernel-based algorithm with all quantitative corrections implemented in the forward model. The Patlak graphical model was used to analyze the ¹⁸F-FDG kinetics in the whole body. The input function was extracted from a region over the descending aorta. For comparison, indirect Patlak analysis from reconstructed frames and direct reconstruction of parametric images from the list-mode data were obtained for the last 30 min of data. Results: Images reconstructed by OSEM showed good quality with low noise, even for the 1-s frames. The image quality was further improved using the kernel method. Total-body Patlak parametric images were obtained using either indirect estimation or direct reconstruction. The direct reconstruction method improved the parametric image quality, having a better contrast-versus-noise tradeoff than the indirect method, with a 2- to 3-fold variance reduction. The kernel-based indirect Patlak method offered image quality similar to the direct Patlak method, with less computation time and faster convergence. Conclusion: This study demonstrated the capability of total-body parametric imaging using the uEXPLORER. Furthermore, the results showed the benefits of kernel-regularized reconstruction and direct parametric reconstruction. Both can achieve superior image quality for tracer kinetic studies compared with the conventional indirect OSEM for total-body imaging.

EXPLORER联盟建造了世界上第一台194厘米长的全身PET / CT扫描仪（uEXPLORER），为临床研究和卫生保健中的人类分子成像提供了一个转化平台。它的全身覆盖范围和超高灵敏度为在生理学，生物化学和药理学研究中进行更精确的示踪动力学分析提供了机会。这项研究的目的是证明全身参数成像的能力，并通过直接和内核重建uEXPLORER数据量化图像质量和动力学参数估计的改进。方法：我们开发了用于动力学分析的定量参数图像重建方法，并将其用于分析第一项人类动态全身PET研究。招募了健康的女性受试者，并在静脉注射256 MBq的¹⁸ F-FDG期间和之后进行了1小时动态扫描。动态数据是使用3维飞行时间列表模式有序子集期望最大化（OSEM）算法和基于内核的算法（在前向模型中实现了所有定量校正）重建的。Patlak图形模型用于分析¹⁸F-FDG在全身的动力学。输入函数是从降主动脉上方的区域提取的。为了进行比较，在最后30分钟的数据中，获得了来自重构帧的间接Patlak分析和来自列表模式数据的参数图像的直接重构。结果：通过OSEM重建的图像即使在1秒帧内也显示出高质量且低噪声。使用核方法进一步改善了图像质量。使用间接估计或直接重建获得全身Patlak参数图像。直接重建方法改善了参数图像质量，比间接方法具有更好的对比度-噪声折衷，方差减小了2到3倍。基于内核的间接Patlak方法提供的图像质量类似于直接Patlak方法，具有更少的计算时间和更快的收敛速度。结论：这项研究证明了使用uEXPLORER进行全身参数成像的能力。此外，结果显示了核正则化重构和直接参数重构的好处。与用于全身成像的常规间接OSEM相比，两者均可在示踪动力学研究中获得卓越的图像质量。