Fig. 5

Recovered ¹⁶⁶Ho activity as a percentage of the known injected activity for ¹⁶⁶Ho filled spheres in the NEMA image quality phantom for various background concentrations of ^99mTc (columns). The top row shows the recovered ¹⁶⁶Ho activity as a function of the number of UMCS-OSEM iterations (8 subsets per iteration) in VOIs matching actual sphere sizes (solid lines) and VOIs with diameters increased by 20 mm (dotted lines). The bottom row shows the recovered ¹⁶⁶Ho activity after 20 iterations as a function of increased VOI diameter (i.e., in addition to the actual sphere size). For clarity, results of only 3 out of the 6 NEMA IQ spheres are shown