(a)
(b)
(c)
(d)
Figure 3: Transaxial slices of the phantom at the level of cylinders with a diameter of 20 mm. (a) Images reconstructed from noise-free projection images using ordered subset expectation maximisation reconstruction. (b) Autoregressive filtering before and after ordered subset expectation maximisation reconstruction. (c) Filtered back projection reconstruction method preceded by Butterworth filtering. (d) Ordered subset expectation maximisation reconstruction followed by Butterworth filtering. Intermediate count level. The images are individually scaled to their own maximum.