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)

Julian M Rogasch; Said Suleiman; Frank Hofheinz; Stephanie Bluemel; Mathias Lukas; Holger Amthauer; Christian Furth

doi:10.1186/s40658-020-0270-y

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)

EJNMMI Phys. 2020 Jan 10;7(1):2. doi: 10.1186/s40658-020-0270-y.

Authors

Julian M Rogasch¹, Said Suleiman², Frank Hofheinz³, Stephanie Bluemel², Mathias Lukas², Holger Amthauer², Christian Furth²

Affiliations

¹ Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Department of Nuclear Medicine, Augustenburger Platz 1, Berlin, Germany. julian.rogasch@charite.de.
² Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Department of Nuclear Medicine, Augustenburger Platz 1, Berlin, Germany.
³ Helmholtz-Zentrum Dresden-Rossendorf, Institute for Radiopharmaceutical Cancer Research, Dresden, Germany.

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.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.

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.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.

Keywords: Contrast recovery; GE Discovery MI; Image reconstruction; PET; PSF; Q.Clear; Signal-to-noise ratio; Spatial resolution; TOF.