Table 1: X-ray filters and applied voltages used in the aluminium phantom scans, with estimated mean photon energies, with and without compensation for the scintillator efficiency.


Filter Applied x-ray source voltage, kV Mean photon energy [ 9 , 10 ], keV Mean photon energy compensated for energy-dependent scintillator efficiency, keV

1 No filter 40 17.1 15.0
2 0.5mm aluminium 50 26.5 22.5
3 1mm aluminium 60 32.1 27.4
4 40 µm copper plus 0.5mm Al (equivalent to ∼2mm Al) 70 38.0 34.0