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Figure 1: Energy spectra of an iodine-123 point source measured by the SPECT-scanner: (a) unshielded I-123 source in air; (b) source shielded with 6-mm lead, showing a broad peak at 172 keV due to reflected high-energy photons; (c) source placed outside the scanner, showing a peak at 121 keV from 90° Compton scattering of 159 keV photons inside the scanner. The main energy window is highlighted with yellow and the second energy window with cyan

Figure 1: Energy spectra of an iodine-123 point source measured by the SPECT-scanner: (a) unshielded I-123 source in air; (b) source shielded with 6-mm lead, showing a broad peak at 172 keV due to reflected high-energy photons; (c) source placed outside the scanner, showing a peak at 121 keV from 90° Compton scattering of 159 keV photons inside the scanner. The main energy window is highlighted with yellow and the second energy window with cyan