Assessment of dual time point protocols to produce parametric K_i images in FDG PET/CT: A virtual clinical study

This simulation study investigated the feasibility of generating Patlak K_i images using a dual time point (DTP-K_i) scan protocol involving two 3-min/bed routine static PET scans and, subsequently, assessed DTP-K_i performance for an optimal DTP scan time frame combination, against conventional Patlak K_i estimated from complete 0-93 min dynamic PET data.

Six realistic heterogeneous tumors of different characteristic spatiotemporal [¹⁸F]FDG uptake distributions for three noise levels commonly found in clinical studies and 20 noise realizations (N = 360 samples) were produced by analytic simulations of the XCAT phantom. Subsequently, DTP-K_i images were generated by performing standard linear indirect Patlak analysis with t* $$ -min (Patlak_{t* = 12}) using a scaled population-based input function (sPBIF) model on 66 combinations of early and late 3-min/bed static whole-body PET reconstructed images. All DTP-K_i images were evaluated against respective DTP-K_i images estimated with Patlak_{t* = 12} and 0-93 min individual input functions (iIFs) and against gold standard K_i images estimated with Patlak_{t* = 12}, 0-93 min iIFs and tissue time activity curves from all reconstructed WB passes 12-93 min post injection. The optimal combination of early and late frames, in terms of attaining the highest correlation between DTP-K_i with sPBIF and gold standard K_i was also determined from a set of 66 different combinations of 2-min early and late frames. Moreover, the performance of DTP-K_i with sPBIF was compared against that of the retention index (RI) in terms of their correlation to the gold standard K_i. Finally, the feasibility and practicality of DTP protocol in the clinic were assessed through the analysis of nine patients.

High correlations (>0.9) were observed between DTP-K_i values from sPBIF and those from iIFs for all evaluated DTP protocols while the mean AUC difference between sPBIF and iIFs was less than 10%. The percentage difference of mean values between DTP-K_i from sPBIF and from iIFs was less than 1%. DTP K_i from sPBIF exhibited significantly higher correlation with gold standard K_i, in contrast to RI, across all 66 DTP protocols (p < 0.05 using the two-tailed t-test by Williams) with the highest correlation attained for the 50-53-min early + 90-93-min late scan time frames (optimal DTP protocol).

Feasibility of generating Patlak K_i [¹⁸F] FDG images from an early and a late post injection 3-min/bed routine static scan using a population-based input function model was demonstrated and an optimal DTP scan protocol was determined. The results indicated high correlations between DTP-K_i and gold-standard K_i images that are significantly larger than those between RI and gold-standard K_i.