Assessment of the short-lived non-pure positron-emitting nuclide 120I for PET imaging

Purpose The non-pure positron-emitting iodine isotope ¹²⁰I (T _1/2=81 min) is a short-lived alternative to ¹²⁴I. ¹²⁰I has a positron abundance more than twice that of ¹²⁴I and a maximum positron energy of 4 MeV. This study was undertaken to evaluate and characterise the qualitative and quantitative PET imaging of ¹²⁰I.Methods ¹²⁰I was produced via the ¹²⁰Te(p,n) reaction on highly enriched ¹²⁰Te. The measurements were done with the Siemens scanner HR+ and the 2D PET scanner GE PC4096+. A cylinder containing three cold inserts and a phantom resembling a human brain slice were used to evaluate half-life, positron abundance and background correction. To analyse the image resolution, a 1-mm tube placed in water was filled with ¹²⁰I and ¹⁸F. Comparisons with ¹⁸F, ¹²⁴I and ¹²³I (measured with SPECT) were made using the Hoffman 3D brain phantom.Results The half-life of 81.1 min was reproduced by the PET measurements. The PET-based positron abundance ranged from 47.9% to 55.0%. The reconstructed image resolution found with the HR+ was 5.4 mm FWHM (12.3 mm FWTM), in contrast to 4.6 mm (8.6 mm) when using ¹⁸F. Erroneous positive and negative numbers of radioactivity found in the cold inserts became nearly zero when the background of γ-coincidences was corrected for. Images of the Hoffman phantom were inferior to those obtained when ¹⁸F or ¹²⁴I was applied but superior to the ¹²³I-SPECT images.Conclusion Our data show that ¹²⁰I of high radionuclidic purity can be regarded as a suitable nuclide for the PET imaging of radioiodine-labelled pharmaceuticals.