Spatial resolution and image quality of radionuclides for PET imaging

Objective This study aims to characterize and compare the saturation limits, spatial resolution, and image quality of various conventional and emerging positron-emitting radionuclides using a preclinical PET/CT scanner. By characterizing the performance of these radionuclides, the study sought to provide insights into their utility in high-resolution PET imaging. Methods Radionuclides ( 18 F, 43 Sc, 45 Ti, 48 V, 52 Mn, 55 Co, 64 Cu, 68 Ga, 89 Zr) were evaluated on a GNEXT PET/CT scanner (Xodus Imaging, Torrance, CA) using saturation and Derenzo phantoms. Saturation was assessed by measuring the deviation between the actual and the region of interest (ROI) activity at varying concentrations of each radionuclide. Spatial resolution was quantified using full-width half maximum (FWHM) measurements from intensity profiles across six Derenzo phantom diameter sizes (1.2 mm–4.8 mm). Signal-to-noise ratios (SNRs) were calculated as a measure of image quality and Bland-Altman plots were used to assess the repeatability of resolution measurements. Statistical comparisons of test-retest were done to evaluate differences in accuracy and consistency across radionuclides. Results Saturation analysis revealed a broad range of limits across radionuclides, with 64 Cu having the highest saturation threshold near 2 mCi (74 MBq), while 52 Mn exhibited the lowest at approximately 250 μCi (9.25 MBq). Spatial resolution was inversely related to positron energy, with radionuclides like 18 F and 64 Cu producing clear images down to rod sizes of 1.6 mm compared to 68 Ga and 55 Co, which showed blurring at the same rod size. SNR analysis confirmed the superior image quality of lower-energy radionuclides, particularly for smaller structures, visually resolvable to 1.6 mm. Bland-Altman analysis showed that across the combination of rod sizes, 18 F displayed improved repeatability in resolution measurements compared to 68 Ga (standard errors of 0.03 and 0.15, respectively). Conclusion This study demonstrates that the physical properties of radionuclides, particularly positron energy, significantly affected PET image quality, spatial resolution, and saturation thresholds. Lower-energy radionuclides like 18 F and 52 Mn are optimal for high-resolution applications, while higher energy radionuclides are better suited for high-activity imaging. These findings provide valuable guidance for optimizing radionuclide selection in preclinical and clinical PET imaging studies.