Performance Evaluation of the PET Component of the IRIS Preclinical PET/CT Scanner and its Capability in Quantitative Dynamic Imaging

Aim The IRIS preclinical PET/CT system has been developed featuring state of the art technology and it is commercially available in a cost effective solution for mice and rats studies. The scanner comprises a full ring PET and a high resolution CT system placed sequentially like in clinical PET/CT scanners. This work presents the performance assessment of the PET component of the system and the evaluation of its capability in quantitative measurements during dynamic imaging studies on mice using short time frames. Materials and methods The PET component of the scanner consists of 16 modular detectors arranged in two octagonal rings. The field-of-view has 95 mm axial coverage and a diameter of 80 mm. Each module comprises a LYSO:Ce matrix of 702 crystals of 1.6 mm × 1.6 mm × 12 mm, with a pitch of about 1.7 mm, coupled to a 64 anodes PMT (Hamamatsu H8500). Images can be reconstructed with both sinogram-based 2D-FBP and LOR-based 3D OS-EM with multi-ray-based system matrix. Attenuation correction is performed with CT-based ?-maps. The PET scanner performance were assessed following the NEMA NU-4 2008 standard. The image uniformity and recovery coefficients were obtained from the image-quality phantom image reconstructed with the 3D ML-EM algorithm. The quantitative capabilities were evaluated both on dedicated phantoms and in mice; dynamic acquisitions with time frames of duration 5-120 s, optimized for image-based estimation of the arterial input function and tracer kinetics in various organs after i.v. injection of 18F-FDG will be presented. Results and Conclusions The spatial resolution, measured as full width at half maximum on single-slice rebinning FBP-reconstructed images, is about 1.5 mm at the center of the field-of-view. The maximum absolute sensitivity for a point source embedded in a 1 cm3 plastic cube and positioned at the center of the field of view is among the highest in the market at about 10% with a 250-650 keV energy window. The image uniformity measured following the NEMA standard is below 5% with the 250-650 keV energy window using ML-EM while the scatter fraction is about 12%. The measured peak NEC is about 200 kcps at 12-13 MBq. The IRIS PET shows a very high sensitivity and a good spatial resolution compared to other existing commercial pre-clinical systems. The overall measured performance makes this new system a powerful but also cost-effective pre-clinical solution for quantitative PET studies.