Reconstructed spatial resolution and contrast recovery with Bayesian penalized likelihood reconstruction (Q.Clear) for FDG-PET compared to time-of-flight (TOF) with point spread function (PSF)

BACKGROUND: Bayesian penalized likelihood reconstruction for PET (e.g., GE Q.Clear) aims at improving convergence of lesion activity while ensuring sufficient signal-to-noise ratio (SNR). This study evaluated reconstructed spatial resolution, maximum/peak contrast recovery (CRmax/CRpeak) and SNR of Q.Clear compared to time-of-flight (TOF) OSEM with and without point spread function (PSF) modeling. METHODS: The NEMA IEC Body phantom was scanned five times (3 min scan duration, 30 min between scans, background, 1.5–3.9 kBq/ml F18) with a GE Discovery MI PET/CT (3-ring detector) with spheres filled with 8-, 4-, or 2-fold the background activity concentration (SBR 8:1, 4:1, 2:1). Reconstruction included Q.Clear (beta, 150/300/450), “PSF+TOF(4/16)” (iterations, 4; subsets, 16; in-plane filter, 2.0 mm), “OSEM+TOF(4/16)” (identical parameters), “PSF+TOF(2/17)” (2 it, 17 ss, 2.0 mm filter), “OSEM+TOF(2/17)” (identical), “PSF+TOF(4/8)” (4 it, 8 ss, 6.4 mm), and “OSEM+TOF(2/8)” (2 it, 8 ss, 6.4 mm). Spatial resolution was derived from 3D sphere activity profiles. RC as (sphere activity concentration [AC]/true AC). SNR as (background mean AC/background AC standard deviation). RESULTS: Spatial resolution of Q.Clear(150) was significantly better than all conventional algorithms at SBR 8:1 and 4:1 (Wilcoxon, each p < 0.05). At SBR 4:1 and 2:1, the spatial resolution of Q.Clear(300/450) was similar or inferior to PSF+TOF(4/16) and OSEM+TOF(4/16). Small sphere CRpeak generally underestimated true AC, and it was similar for Q.Clear(150/300/450) as with PSF+TOF(4/16) or PSF+TOF(2/17) (i.e., relative differences < 10%). Q.Clear provided similar or higher CRpeak as OSEM+TOF(4/16) and OSEM+TOF(2/17) resulting in a consistently better tradeoff between CRpeak and SNR with Q.Clear. Compared to PSF+TOF(4/8)/OSEM+TOF(2/8), Q.Clear(150/300/450) showed lower SNR but higher CRpeak. CONCLUSIONS: Q.Clear consistently improved reconstructed spatial resolution at high and medium SBR compared to PSF+TOF and OSEM+TOF, but only with beta = 150. However, this is at the cost of inferior SNR with Q.Clear(150) compared to Q.Clear(300/450) and PSF+TOF(4/16)/PSF+TOF(2/17) while CRpeak for the small spheres did not improve considerably. This suggests that Q.Clear(300/450) may be advantageous for the 3-ring detector configuration because the tradeoff between CR and SNR with Q.Clear(300/450) was superior to PSF+TOF(4/16), OSEM+TOF(4/16), and OSEM+TOF(2/17). However, it requires validation by systematic evaluation in patients at different activity and acquisition protocols.