Optimization and assessment of quantitative 124 I imaging on a Philips Gemini dual GS PET/CT system

Purpose Quantitative 124 I PET imaging is challenging as 124 I has a complex decay scheme. In this study the performance of a Philips Gemini dual GS PET/CT system was optimized and assessed for 124 I. Methods The energy window giving the maximum noise equivalent count rate (NECR) and NEMA 2001-NU2 image quality were measured. The activity concentration (AC) accuracy of images calibrated using factors from 18 F and 124 I decaying source measurements were investigated. Results The energy window 455–588 keV gave the maximum NECR of 9.67 kcps for 233 MBq. 124 I and 18 F image quality was comparable, although 124 I background variability was increased. The average underestimation in AC in 124 I images was 17.9 ± 2.9% for nonuniform background and 14.7 ± 2.9% for single scatter simulation (SSS) subtraction scatter correction. At 224 MBq the underestimation was 10.8 ± 11.3%, which is comparable to 7.7 ± 5.3% for 18 F, but increased with decreasing activity. Conclusions The best 124 I PET quantitative accuracy was achieved for the optimized energy window, using SSS scatter correction and calibration factors from decaying 124 I source measurements. The quantitative accuracy for 124 I was comparable to that for 18 F at high activities of 224 MBq but diminishing with decreasing activity. Specific corrections for prompt γ-photons may further improve the quantitative accuracy.