Impact of time-of-flight (TOF) and point-spread-function (PSF) PET on whole-body oncologic studies

Objectives: To evaluate the image quality (IQ) of the different reconstruction algorithms in the novel hybrid Discovery 690 PET/CT system (GE Medical Systems) for both TOF and PSF. Methods: 32 patients (pts) underwent to FDG PET/CT scan (D-690). 78 FDG enhanced malignant lesions (< 1.5 cm) were evaluated. For each pt, image reconstruction was performed by using the following algorithms: HD (conventional reconstruction: 3D-OSEM),TOF (3D-OSEM+TOF), PSF (3D-OSEM+PSF),TOFPSF (3D-OSEM+TOF+PSF) reconstructed at 3 and 5 iterations (IT). For each image set, IQ was evaluated in a blind by 3 observers using a score from 1 to 5 (best) considering: contrast, noise and image resolution.A semi-quantitative evaluation was also performed measuring the SUVmax for each lesion in the different reconstructions. Results: TOFPSF at 5-ITs showed the highest score in 97% of the scans and for all the observers. At 3-ITs TOFPSF was judged better than TOF,PSF and HD by all observers.SUVmax showed a trend similar to that of the qualitative evaluations with a mean difference between TOFPSF(5-IT) and HD >50%. Conclusions: The new reconstructions algorithms accounting for TOF and PSF allow a significant improvement of IQ, in particular of signal/noise ratio, as well as spatial resolution, when compared to the conventional reconstruction. The best result was obtained when both TOF and PSF were used together. The TOFPSF algorithm is valuable for clinical applications. An optimization of the reconstruction parameters, in particular in number of ITs, could lead to an improvement of diagnostic accuracy