331. Performance of point spread function reconstruction algorithm on a new PET-CT TOF scanner

Abstract

Purpose Aim of this study was to evaluate the performance of PSF reconstruction algorithm of a PET-TC TOF scanner. Comparison in term of image quality was performed in order to investigate potentialities and differences between PSF algorithm and the standard OSEM algorithm routinely applied in the clinical use. Methods The phantom NEMA 2012 Body Image Quality (18F, 213 kBq/ml, □ 10 mm 13 mm 17 mm 22 mm hot spheres (background ratio 4 ÷ 1 ), □ 28 mm 37 mm cold spheres) was acquired with Philips IngenuityTF PET-TC scanner (TOF, AC-SC). Raw data were reconstructed both with standard OSEM 3D and with PSF, using 20 different paired iteration values (1–500) and regularization levels (1–20). Seven regions of interest (ROIs) were contoured: 4 centred on “hot” spheres, 2 on “cold” spheres and 1 on background. Mean value (MV) and standard deviation (SD) of every ROI were calculated: signal to noise ratio (SNR) and contrast to noise ratio (CNR) were compared. Spatial resolution was evaluated as steepness of the 10 mm-sphere profile. Results PSF images showed resolution higher (e.g. 3 mm for 30 iterations) than the standard OSEM (6 mm). As shown in figure 1a the more iteration number the higher artifacts presence, especially in the background region. MV and SD values relative to the “hot spheres” strongly depend on iteration number and regularization level; variations up to +1000% were found (500 iterations and 20 regularization) both on MV and SD values. No variations were noticed on background MV, but SD values increase up to +600%. As consequence SNR and CNR are affected by reconstruction parameters (Fig. 1b). Conclusions PSF images showed resolution higher than standard OSEM, but also huge artifacts and unacceptable variations in measured activity (and SUV). The use of PSF reconstruction for quantitative purposes is not recommended and its use should be designed for specific uses.