A Prior-Guided Joint Diffusion Model in Projection Domain for PET Tracer Conversion

Positron emission tomography (PET) is widely used to assess metabolic activity, but its application is limited by the availability of radiotracers. 18F-labeled fluorodeoxyglucose (18F-FDG) is the most commonly used tracer but shows limited effectiveness for certain tumors. In contrast, 6-18F-fluoro-3,4-dihydroxy-L-phenylalanine (18F-DOPA) offers higher specificity for neuroendocrine tumors and neurological disorders. However, its complex synthesis and limitations in transportation and clinical use hinder widespread adoption. During PET imaging, the sinogram represents a form of raw data acquired by the scanner. Therefore, modeling in projection domain enables more direct utilization of the original information, potentially reducing the accumulation of errors introduced during the image reconstruction process. Inspired by these factors, this study proposes a prior-guided joint diffusion model (PJDM) for transforming 18F-FDG PET images into 18F-DOPA PET images in projection domain. Specifically, a coarse estimation model and a prior refinement model are trained independently. During inference, an initial synthetic 18F-DOPA PET sinogram is generated using a higher-order hybrid sampler. This sinogram is then degraded and serves as an additional condition to guide the iterative refinement process using learned prior. Experimental results demonstrated that PJDM effectively improved both sinogram quality and synthetic outcomes. The code is available at: this https URL.

@article{chen2025_2506.16733,
  title={ A Prior-Guided Joint Diffusion Model in Projection Domain for PET Tracer Conversion },
  author={ Fang Chen and Weifeng Zhang and Xingyu Ai and BingXuan Li and An Li and Qiegen Liu },
  journal={arXiv preprint arXiv:2506.16733},
  year={ 2025 }
}