Patlak-PBNT: a simple population-based Patlak model to generate [⁶⁸Ga]Ga-PSMA-11 K_i parametric images for shortened total-body PET scan

Purpose: The objective of this study is to generate reliable K_i parametric images from short-duration total-body PET scan for clinical applications using a simple population-based Patlak model. Methods: We proposed a population-based Patlak model named Patlak-PBNT, which incorporates a population-based “normalized time” (PBNT) into the traditional Patlak plot. This model does not require long-duration PET scans to obtain an image-derived input function (IDIF) of full measured kinetics, thereby generating reliable K_i images from short-duration total-body PET scans. We evaluated the effectiveness of Patlak-PBNT based on 60-minute full-dynamic total-body [⁶⁸Ga]Ga-PSMA-11 PET data collected from 20 subjects PET scans. For comparison, the K_i images generated by the traditional Patlak plot (t* = 20 min post-injection) with measured IDIF was used as the gold standard. The differences between Patlak-PBNT-generated K_i images and the gold standard were evaluated at both the voxel and volume of interest (VOI) levels. Results: Compared to the traditional Patlak, Patlak-PBNT effectively reduces PET scan duration while maintaining the quality of generated K_i images. For [⁶⁸Ga]Ga-PSMA-11, K_i images generated by Patlak-PBNT using only 40 minute dynamic PET images (20–60 min post-injection) show negligible differences compared to those generated by traditional Patlak with the same 40 minute dynamic PET images and a 60 minute full-duration IDIF, with a normalized mean squared error (NMSE) of 0.01, a Pearson correlation coefficient (Pearson’s r) of 0.99, and a peak signal-to-noise ratio (PSNR) of 75.27 dB. It is important to note that K_i images generated by Patlak-PBNT, using only 20 minute dynamic PET images (40–60 min post-injection), exhibit a high correlation with the gold standard in predefined VOIs, achieving a coefficient of determination (R²) of 0.92. Conclusion: The proposed Patlak-PBNT model reduces the dependency on a complete input function, thereby avoiding the need for long-duration PET scans typically required to obtain a full input function. When utilizing dynamic PET images of identical scan durations (20–60 min post-injection), the K_i images generated by Patlak-PBNT and traditional Patlak are essentially identical. Furthermore, even when the scan duration is further reduced, the Patlak-PBNT method is capable of quantifying 20 minute dynamic [⁶⁸Ga]Ga-PSMA-11 total-body PET images.