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Background  Block-sequential regularized expectation maximization (BSREM), commercially Q. Clear (GE Healthcare, Milwaukee, WI, USA), is a reconstruction algorithm that allows for a fully convergent iterative reconstruction leading to higher image contrast compared to conventional reconstruction algorithms, while also limiting noise. The noise penalization factor  β  controls the trade-off between noise level and resolution and can be adjusted by the user. The aim was to evaluate the influence of different  β  values for different activity time products (ATs = administered activity × acquisition time) in whole-body  18 F-fluorodeoxyglucose (FDG) positron emission tomography with computed tomography (PET-CT) regarding quantitative data, interpretation, and quality assessment of the images.  Twenty-five patients with known or suspected malignancies, referred for clinical  18 F-FDG PET-CT examinations acquired on a silicon photomultiplier PET-CT scanner, were included. The data were reconstructed using BSREM with  β  values of 100–700 and ATs of 4–16 MBq/kg × min/bed (acquisition times of 1, 1.5, 2, 3, and 4 min/bed). Noise level, lesion SUV max , and lesion SUV peak  were calculated. Image quality and lesion detectability were assessed by four nuclear medicine physicians for acquisition times of 1.0 and 1.5 min/bed position.    Results  The noise level decreased with increasing  β  values and ATs. Lesion SUV max  varied considerably between different  β  values and ATs, whereas SUV peak  was more stable. For an AT of 6 (in our case 1.5 min/bed), the best image quality was obtained with a  β  of 600 and the best lesion detectability with a  β  of 500. AT of 4 generated poor-quality images and false positive uptakes due to noise.    Conclusions  For oncologic whole-body  18 F-FDG examinations on a SiPM-based PET-CT, we propose using an AT of 6 (i.e., 4 MBq/kg and 1.5 min/bed) reconstructed with BSREM using a  β  value of 500–600 in order to ensure image quality and lesion detection rate as well as a high patient throughput. We do not recommend using AT < 6 since the risk of false positive uptakes due to noise increases.

ejnmmi research

Impact of acquisition time and penalizing factor in a block-sequential regularized expectation maximization reconstruction algorithm on a Si-photomultiplier-based PET-CT system for 18F-FDG