*3.3. Reproducibility*

For each sphere of the Image Quality phantom, the RCavg calculated in the acquisitions with short, medium and long acquisition times (1, 2 and 5 min per bed position), and T/B ratios of 10:1 and 20:1 were averaged and the COV was determined to assess reproducibility considering varying scan parameters. Scans with acquisition times of 2.5 and 10 min per bed position were omitted as these results are similar to 2 and 5 min per bed position, respectively. As shown in Figure 4, the averaged RCavg decreases as β increases, with the largest differences for the RCavg of the smallest sphere. For the largest 4 spheres, the COV decreases as β increases. The COV for the 10 and 13 mm-diameter spheres exhibit an inverse opposite relation as differences in RCavg between the two T/B ratios arise for increasing β. Due to the construction of the prior, the noise penalty term depends on the relative difference in values of adjacent voxels, with higher relative differences yielding

better edge preservation. This mainly affects the voxels at the edge of a sphere and hence the RCmax and correspondingly the RCavg of bigger spheres is less affected. For spheres consisting of only a few voxels, however, RCmax and RCavg will slightly decrease. For the 10 mm-diameter sphere, the minimum COV is found at β = 600. For lower β values, the COV increases as a result of increasing RCavg for shorter acquisition times. This increase corresponds to an increase in RCmax which is explained by the higher relative noise level for low count acquisitions. Again, the effect is most profound in small spheres as the number of counts within the region and the maximum number of counts collected in a voxel is smaller than in larger spheres.

**Figure 4.** Averaged RCavg and COV from the Image Quality phantom. Averaged RCavg over 6 reconstructions with varying acquisition times per bed position (1, 2 and 5 min) and T/B ratios (10:1 and 20:1).
