Fig. 10

Dead-time-corrected SPECT sensitivity (observed primary photons count rate per activity) as a function of activity (a), photopeak count rate (b, 187–226 keV) and wide-spectrum count rate (c, 18–680 keV). The vertical coloured dotted line indicates, for each phantom, the maximum quantifiable activity and usable photopeak count rate, which are both geometry-dependant (a and b, respectively; those of the CTDI-16 phantom could not be precisely determined due to missing points at high activity). The vertical black dotted line corresponds to the unique, geometry-independent maximum wide-spectrum count rate of the SPECT system (c; ~350 kcps). The capped horizontal lines show, for each phantom, the low-count rate acquisition data points that could be used for calibration factor determination with Method A (low-activity CF; Table 4), i.e. data points with less than 1% dead time but without excessive sensitivity overestimation (upward tailing) at very low count rate (Table 4). Planar data (Air-2D, averaged for both detectors) is shown for comparison