Fig. 4.

Box and whiskers plots showing SUVmax and CR distributions obtained from lesions in 25 patients. The left side shows SUVmax (a, c, and e), and the right side CR (b, d, and f). The top row (a, b) shows the group with small size and low-uptake lesions (N = 8), the middle row (c, d) shows the group with medium size and medium uptake lesions (N = 15), and the bottom row (e, f) shows the group with large size or high-uptake lesions (N = 17). Each subplot shows from left to right the results of the TOF OSEM reconstructions with 28 subsets and 2 and 3 iterations, followed by TOF BSREM reconstructions with regularization parameter β = 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700, 800, 900, 1000, 1200. H indicates significantly higher values and L indicates significantly lower parameter values for TOF BSREM compared to reference TOF OSEM. CR = the tumor to background ratio of the indicated TOF reconstruction compared to the reference TOF OSEM reconstruction with 2 iterations and 28 subsets (Eq. 3), a CR value higher than 1 indicates a better tumor to background ratio for BSREM compared to OSEM. TOF time-of-flight, SUV standardized uptake value, SUVmax the average of the hottest 5 voxels in the lesion, OSEM ordered subset expectation maximization, BSREM block sequential regularized expectation maximization