Spatial resolution and image quality of radionuclides for PET imaging

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.

Radionuclides (¹⁸F, ⁴³Sc, ⁴⁵Ti, ⁴⁸V, ⁵²Mn, ⁵⁵Co, ⁶⁴Cu, ⁶⁸Ga, ⁸⁹Zr) 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.

Saturation analysis revealed a broad range of limits across radionuclides, with ⁶⁴Cu having the highest saturation threshold near 2 mCi (74 MBq), while ⁵²Mn exhibited the lowest at approximately 250 μCi (9.25 MBq). Spatial resolution was inversely related to positron energy, with radionuclides like ¹⁸F and ⁶⁴Cu producing clear images down to rod sizes of 1.6 mm compared to ⁶⁸Ga and ⁵⁵Co, 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, ¹⁸F displayed improved repeatability in resolution measurements compared to ⁶⁸Ga (standard errors of 0.03 and 0.15, respectively).

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 ¹⁸F and ⁵²Mn 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.