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

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