Quantitative imaging of yttrium-86 PET with the ECAT EXACT HR+ in 2D mode.

The radionuclide 86Y potentially allows for the precise assessment of tissue radioactivity biodistribution and, thus, extrapolation of a therapeutic dose of 90Y-labeled compounds. A method to obtain quantitative images from 86Y-PET measurements after a background correction and a recalibration is presented. Cylinder and body phantom measurements with 18 F and 86Y using an ECAT EXACT HR+ tomograph were performed in 2D mode. A second-order series expansion is used to correct for the background of spurious coincidences in the sinogram. A recalibration of the positron emission tomography (PET) system, depending on the ratio of true coincidences and singles, is implemented. The correction for the nonannihilation coincidences with a second-order series expansion significantly improves the accuracy of quantitation: The lesion-to-background ratio is reproduced, and the variation of the activity concentration in the homogeneous background regions of the phantoms is smaller than 5%. The apparent activities in cold inserts of various densities is reduced to less than 15% of the concentration in the active region. The recalibration of the system works with a relative error of 0.2% +/- 2.4%. In conclusion, the used approximations lead to improved uniformity and quantitative accuracy in 86Y-PET measurements with the ECAT EXACT HR+.