Characterization of the short-lived non-pure positron emitter 120I for PET imaging

The non-pure beta(+)-emitting iodine-isotope I-120 is potentially a short-lived alternative to I-124 for PET imaging. I-120 has a half-life of 81 min and a maximum beta(+)-energy of 4 MeV. Literature data on beta(+)-abundance are rather uncertain. This study evaluates parameters important for PET imaging of I-120 and characterizes PET measurements using this isotope. I-120 was produced via the Te-122(p,3n) and Te-120(p,n) reactions, the latter of which led to only very small impurities of I-120m and I-119. PET measurements were done with a brain-slice shaped phantom consisting of a gray (GM) and a white matter (WM) chamber. A 1mm line source positioned in the occipital part of this phantom was filled with I-120 or F-18. Comparative studies using the Hoffman 3D-brain phantom were done with I-120, F-18, I-124, and I-123 (measured with SPECT). The measurements were evaluated with respect to the half-life, beta(+)-abundance, image resolution and GM/WM contrast. For all measurements reported here the 2D PET-scanner GE PC4096+ was used. The measured half-life was 82.4min, and the beta(+)-abundance 52 +/- 5%. The reconstructed image resolution was 9.7 mm FWHM compared to 7.5 mm when F-18 was used. The GM/WM contrast was underestimated by about 10%. Images of the brain phantom revealed an image quality inferior to that when F-18 or I-124 was applied, but better than the I-123-SPECT image. Our data show that I-120 of high radionuclidic purity produced by the Te-120(p,n) reaction can be regarded as a suitable radionuclide for the PET-imaging of iodine-labeled radiopharmaceuticals.