Abstract
Rationale: 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 healthcare. 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 is 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 one-hour dynamic scan was acquired during and following an intravenous injection of 256 MBq of 18F-FDG. Dynamic data were reconstructed using a 3D TOF list-mode 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 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 show good image quality with low noise, even for the 1-s frames. The image quality was further improved by using the kernel method. Total-body Patlak parametric images were obtained by using either indirect estimation or direct reconstruction. The direct reconstruction method was found to improve parametric image quality with better contrast versus background noise tradeoff compared to the indirect method with a 2-3 fold variance reduction. The kernel-based indirect Patlak method offered similar image quality as the direct Patlak 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 to the conventional indirect OSEM for total-body imaging.
- Image Reconstruction
- PET
- Radiotracer Tissue Kinetics
- Positron emission tomography
- direct reconstruction
- kernel method
- parametric imaging
- tracer kinetics
- Copyright © 2019 by the Society of Nuclear Medicine and Molecular Imaging, Inc.