Benchmarking ¹⁸F and ⁶⁸Ga Phantom Performance on a Digital Time-of-Flight PET/CT System: Reference Values for Spatial...

Our purpose was to establish reference performance benchmarks for spatial resolution, contrast recovery coefficient (CRC), and background variability (BV) for ⁶⁸Ga and ¹⁸F under matched conditions and to determine the extent to which acquisition duration can compensate for isotope-specific resolution differences. Methods: Phantom studies were performed on a digital PET/CT platform using capillary sources in air (minimal scatter) and a triple-line insert in water (scatter conditions). A National Electrical Manufacturers Association International Electrotechnical Commission body phantom (spheres 10-37 mm; 4:1 activity ratio) was used to assess CRC (International Atomic Energy Agency definition) and BV (coefficient of variation). Data were analyzed using Kruskal-Wallis tests for resolution and 2-way ANOVA for CRC/BV, evaluating the interaction between isotope and acquisition duration. Results: ¹⁸F consistently yielded resolution limits (full width at half maximum) superior to those of ⁶⁸Ga in both air and water (Kruskal-Wallis, P ∼ 0.008). Notably, extending the acquisition duration from 2 to 5 min provided no significant improvement in full width at half maximum for either tracer (P = 0.70). In National Electrical Manufacturers Association testing, ¹⁸F maintained a significant CRC advantage across all sphere sizes and durations. At 10 min, the CRC for the 37-mm sphere reached about 97.5% for ¹⁸F versus about 81.3% for ⁶⁸Ga. For small spheres (10-13 mm), ¹⁸F exceeded ⁶⁸Ga recovery by about 14%-22%. Although increasing scan duration from 2 to 10 min significantly reduced BV (noise) for both tracers (¹⁸F: 1.92%→1.37%; ⁶⁸Ga: 2.47%→1.29%; P = 0.026), it did not bridge the CRC gap. Conclusion: This work provides practical benchmark values for ¹⁸F and ⁶⁸Ga on a digital PET/CT platform. Under matched reconstruction conditions, ¹⁸F retained superior intrinsic resolution and contrast recovery, whereas longer acquisitions mainly reduced noise and could not overcome the physical resolution limitations of ⁶⁸Ga. These data support quality assurance, protocol optimization, and harmonization of prostate-specific membrane antigen PET imaging across both tracers.