Fig. 4

Activity in each sphere measured from the mean counts in the images divided by the known, physical activity in each sphere plotted against activity concentration. The figure shows the results obtained with the filtered 30 × 4 reconstruction, with ME 239 keV in panel a, ME 79 keV in panel b, HE 239 keV in panel c, and HE 79 keV in panel d. Equivalent figures for the other reconstructions with and without filters applied can be found in the supplementary material. The mean activity ratio for the sphere volume is shown as a line. Of note, the x-axes are the same, but the values on the y-axes differ