Fig. 4

Recovered ¹⁶⁶Ho activity as a percentage of the known injected activity for ¹⁶⁶Ho filled spheres in the NEMA image quality phantom, after 20 iterations (8 subsets). Three subsequent acquisitions were performed with ^99mTc background activity concentrations of 0, 6, and 11 kBq/ml (squares, triangles, and circles, respectively). Mean activity concentrations were measured in volumes of interest (VOIs) matching the actual sphere sizes (solid lines), and in VOIs with diameters increased by 20 mm (dotted lines)