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)

Abstract

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.