Reconstructed spatial resolution and contrast recovery with Bayesian penalized likelihood reconstruction (Q.Clear)...

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.

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).

Spatial resolution of Q.Clear₁₅₀ 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.

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.Clear₁₅₀ 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.