Image quality vs. NEC in 2D and 3D PET

To investigate the relationship between NEC and image quality to 2D and 3D PET, while simultaneously optimizing 3D low energy threshold (LET), we have performed a series of phantom measurements. The phantom consisted of 46 1 cm fillable hollow spheres on a random grid inside a water-filled oval cylinder, 21 cm tall, 36 cm wide, and 40 cm long. The phantom was imaged on a Discovery ST PET/CT system (GE Healthcare, Milwaukee, WI) in a series of 3 min scans as it decayed from an activity of 7.2 mCi. The scans included LET settings of 375,400, and 425 keV in 3D, and 375 keV in 2D. Image signal-to-noise (SNR) was calculated and compared wash NEC. While both NEC and image quality in 3D improved for LETs above the default of 375 keV, we found that there were significant differences between NEC and image quality for 2D and 3D. Most importantly, 3D image-quality was strongly dependent on the reconstruction algorithm and its associated parameters. In conclusion, a direct measure of image quality as necessary for comparing 2D vs. 3D performance.