Abstract
BackgroundBayesian 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.MethodsThe 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+TOF4/16” (iterations, 4; subsets, 16; in-plane filter, 2.0 mm), “OSEM+TOF4/16” (identical parameters), “PSF+TOF2/17” (2 it, 17 ss, 2.0 mm filter), “OSEM+TOF2/17” (identical), “PSF+TOF4/8” (4 it, 8 ss, 6.4 mm), and “OSEM+TOF2/8” (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).ResultsSpatial 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.Clear300/450 was similar or inferior to PSF+TOF4/16 and OSEM+TOF4/16. Small sphere CRpeak generally underestimated true AC, and it was similar for Q.Clear150/300/450 as with PSF+TOF4/16 or PSF+TOF2/17 (i.e., relative differences < 10%). Q.Clear provided similar or higher CRpeak as OSEM+TOF4/16 and OSEM+TOF2/17 resulting in a consistently better tradeoff between CRpeak and SNR with Q.Clear. Compared to PSF+TOF4/8/OSEM+TOF2/8, Q.Clear150/300/450 showed lower SNR but higher CRpeak.ConclusionsQ.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.Clear300/450 and PSF+TOF4/16/PSF+TOF2/17 while CRpeak for the small spheres did not improve considerably. This suggests that Q.Clear300/450 may be advantageous for the 3-ring detector configuration because the tradeoff between CR and SNR with Q.Clear300/450 was superior to PSF+TOF4/16, OSEM+TOF4/16, and OSEM+TOF2/17. However, it requires validation by systematic evaluation in patients at different activity and acquisition protocols.
Highlights
Bayesian penalized likelihood reconstruction for positron emission tomography (PET) (e.g., GE Q.Clear) aims at improving convergence of lesion activity while ensuring sufficient signal-tonoise ratio (SNR)
This study evaluated reconstructed spatial resolution, maximum/ peak contrast recovery (CRmax/CRpeak) and SNR of Q.Clear compared to time-offlight (TOF) ordered subset expectation maximization (OSEM) with and without point spread function (PSF) modeling
Q.Clear consistently improved reconstructed spatial resolution at high and medium signal-to-background ratio (SBR) compared to PSF+TOF and OSEM+TOF, but only with beta = 150
Summary
Bayesian penalized likelihood reconstruction for PET (e.g., GE Q.Clear) aims at improving convergence of lesion activity while ensuring sufficient signal-tonoise ratio (SNR). While TOF mainly improves signal-to-noise ratio (SNR) at comparable convergence level [1] and leaves standardized uptake values (SUV) comparably unaffected [2, 3], PSF primarily increases reconstructed spatial resolution [4, 5] and has shown SUVmax increases by > 30% in clinical studies [2, 3] Both TOF and PSF benefit the tradeoff between contrast recovery (CR) and SNR, but all conventional reconstruction methods share the principle limitation that adequate CR by increasing numbers of iterations/subsets will be at the cost of decreasing SNR. Previous studies that compared Q.Clear and conventional methods by only evaluating isolated reconstruction settings may be of limited representativeness
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