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Background  Block-sequential regularized expectation maximization (BSREM) is a fully convergent iterative image reconstruction algorithm. We hypothesize that tracers with different distribution patterns will result in different optimal settings for the BSREM algorithm. The aim of this study was to evaluate the image quality with variations in the applied  β -value and acquisition time for three positron emission tomography (PET) tracers. NEMA image quality phantom measurements and  c linical whole-body digital time-of-flight (TOF) PET/computed tomography (CT) examinations with  68 Ga-DOTATOC ( n  = 13),  18 F-fluoride ( n  = 10), and  11 C-acetate ( n  = 13) were included. Each scan was reconstructed using BSREM with  β -values of 133, 267, 400, and 533, and ordered subsets expectation maximization (OSEM; 3 iterations, 16 subsets, and 5-mm Gaussian post-processing filter). Both reconstruction methods included TOF and point spread function (PSF) recovery. Quantitative measures of noise, signal-to-noise ratio (SNR), and signal-to-background ratio (SBR) were analysed for various acquisition times per bed position (bp).    Results  The highest  β -value resulted in the lowest level of noise, which in turn resulted in the highest SNR and lowest SBR. Noise levels equal to or lower than those of OSEM were found with  β -values equal to or higher than 400, 533, and 267 for  68 Ga-DOTATOC,  18 F-fluoride, and  11 C-acetate, respectively. The specified  β -ranges resulted in increased SNR at a minimum of 25% ( P  < 0.0001) and SBR at a maximum of 23% ( P  < 0.0001) as compared to OSEM. At a reduced acquisition time by 25% for  68 Ga-DOTATOC and  18 F-fluoride, and 67% for  11 C-acetate, BSREM with  β -values equal to or higher than 533 resulted in noise equal to or lower than that of OSEM at full acquisition duration (2 min/bp for  68 Ga-DOTATOC and  18 F-fluoride, 3 min/bp for  11 C-acetate). The reduced acquisition time with  β  533 resulted in increased SNR (16–26%,  P  < 0.003) and SBR (6–18%,  P  < 0.0001 ( P  = 0.07 for  11 C-acetate)) compared to the full acquisition OSEM.    Conclusions  Within tracer-specific ranges of  β -values, BSREM reconstruction resulted in increased SNR and SBR with respect to conventional OSEM reconstruction. Similar SNR, SBR, and noise levels could be attained with BSREM at relatively shorter acquisition times or, alternatively, lower administered dosages, compared to those attained with OSEM.

ejnmmi physics

Evaluation of block-sequential regularized expectation maximization reconstruction of 68Ga-DOTATOC, 18F-fluoride, and 11C-acetate whole-body examinations acquired on a digital time-of-flight PET/CT scanner