Background: Both image quality and quantitative accuracy of PET depend on several factors such as uptake time, scanner characteristics and image reconstruction methods. Ordered subset expectation maximization (OSEM) is considered today the gold standard for image reconstruction. Penalized-likelihood estimation (PL) algorithms have been recently developed for PET reconstruction to improve quantitation accuracy while maintaining or even improving image quality. In the present study, we aim to compare the performance of a PL algorithm (Q.Clear, GE Healthcare) and 3D OSEM for 68Ga-DOTATATE (68Ga-DOTA) PET studies, both visually and quantitatively. Thirty consecutive whole-body 68Ga-DOTA studies were included. The data were acquired in list mode and reconstructed using 3D OSEM and Q.Clear with various values of the regularization parameter β, and various acquisition times per bed position (bp), thus generating images with reduced injected dose (1.5 min/bp: β=300-1100; 1.0 min/bp: β=600-1300 and 0.5 min/bp: β=800-2200). Evaluation was performed using a phantom and clinical data. Finally, two experienced nuclear medicine physicians blinded to the variables assessed the image quality visually.
Results: Clinical images reconstructed with Q.Clear , set at 1.5 and 1.0 min/bp using β = 1100 and 1300 respectively, resulted in images with noise equivalence to 3D OSEM (1.5 min/bp) with a mean increase in SUVmax of 14 % and 11%, in SNR of 18% and 10%, and in SBR of 14% and 12%, respectively. Reconstruction using 0.5 min/bp and β = 2200 resulted in SUVmax, SNR and SBR with a relative difference < 1%. Visual assessment yielded similar results with mean scores for Q.Clear (1.5, 1.0 and 0.5 min/bp) vs 3D OSEM (1.5 min/bp) of 3.58 vs 3.38, 3.64 vs 3.47 and 3.60 vs 3.61, respectively.
Conclusion: 68Ga-DOTA reconstructions with Q.Clear, 1.5 and 1.0 min/bp resulted in increased tumor SUVmax and in improved SNR and SBR at a similar level of noise compared to 3D OSEM. Q.Clear with β =1300 enabled a one-third reduction of acquisition time or injected dose, with similar image quality compared to 3D OSEM.