Fig 1.
Imaging setup (a) and source distribution of ellipsoid phantom (b). The blue dotted line in (b) represents the region of interest for the semi-quantitative and uniformity tests.
Fig 2.
Examples of the line profile for spatial resolution analysis.
The two point sources are said to be distinct when the maximum values in both x<0 and x>0 are larger than the value of x = 0 in the profile of y = 0 (the origin was defined as the centre of the images). (A): distinguishable, (B): indistinguishable.
Fig 3.
Images of two point sources with 8 mm distance (A)—(E) and spatial resolutions of the images reconstructed by the various algorithms (F).
Fig 4.
Images reconstructed using the various algorithms.
Numbers in brackets denote the number of iterations for SOE (10 times more than for OS-EM and MRP-EM).
Fig 5.
Changes in RSS, ZNCC, and MI of the reconstructed image for each iterative algorithm (OS-EM: blue, MRP-EM: red and SOE: green). Lower values are preferable for RSS, and higher values are better for ZNCC and MI. The x-axis value (iteration number) of SOE is 10 times greater than that of OS-EM and MRP-EM. The RSS, ZNCC, and MI values of BP were 2.8×10−5, 0.35, and 0.43, respectively, and those of the analytical method were 2.0×10−5, 0.88, and 0.76, respectively.
Fig 6.
Changes in average and CV of HS, LE, CS1, CS2, and BG of the reconstructed images for each iterative algorithm (OS-EM: blue, MRP-EM: red and SOE: green). The x-axis value (iteration number) of SOE is 10 times greater than that of OS-EM and MRP-EM. The average values (CV) of HS, LE, CS1, CS2, and BG for the analytical method were 1.0×10−4 (6.8%), 4.1×10−5 (10%), 1.6×10−5 (36%), 1.0×10−5 (73%), and 9.3×10−6 (65%), and those for BP were 6.8×10−5 (3.6%), 3.0×10−5 (12%), 4.1×10−5 (3.0%), 3.7×10−5 (4.8%), and 1.3×10−5 (23%).
Fig 7.
Comparison of image quality of BP, Analytic algorithm, OS-EM with 10 iterations, MRP-EM with 20 iterations, and SOE with 200 iterations.
(a) Reconstruction time (shorter is better), (b) spatial resolution (shorter is better), (c) RSS (smaller is better), (d) ZNCC (higher is better), (e) MI (higher is better), (f) average values in each position, and (g) CV in each position.