Q.Clear reconstruction for reducing the scanning time for ${}^{68}$Ga-DOTA-FAPI-04 PET/MR imaging

This study aims to determine whether Q.Clear positron emission tomography (PET) reconstruction may reduce tracer injection dose or shorten scanning time in ${}^{68}$GaGallium-labelled fibroblast activation protein inhibitor (${}^{68}$Ga-FAPI) PET/magnetic resonance (MR) imaging. We retrospectively collected cases of ${}^{68}$Ga-FAPI whole-body imaging performed on integrated PET/MR. PET images were reconstructed using three different methods: ordered subset expectation maximization (OSEM) reconstruction with full scanning time, OSEM reconstruction with half scanning time, and Q.Clear reconstruction with half scanning time. We then measured standardized uptake values (SUVs) within and around lesions, alongside their volumes. We also evaluated image quality using lesion-to-background (L/B) ratio and signal-to-noise ratio (SNR). We then compared these metrics across the three reconstruction techniques using statistical methods. Q.Clear reconstruction significantly increased SUV${}_{max}$ and SUV${}_{mean}$ within lesions (more than 30%) and reduced their volumes in comparison with OSEM reconstruction. Background SUV${}_{max}$ also increased significantly, while background SUV${}_{mean}$ showed no difference. Average L/B values for Q.Clear reconstruction were only marginally higher than those from OSME reconstruction with half-time. SNR decreased significantly in Q.Clear reconstruction compared with OSEM reconstruction with full time (but not half time). Differences between Q.Clear and OSEM reconstructions in SUV${}_{max}$ and SUV${}_{mean}$ values within lesions were significantly correlated with SUVs within lesions. Q.Clear reconstruction was useful for reducing PET injection dose or scanning time while maintaining the image quality. Q.Clear may affect PET quantification, and it is necessary to establish diagnostic recommendations based on Q.Clear results for Q.Clear application.