Table 2.

Summary of terms used in theoretical description of NPS. Nominal values correspond to a typical CBCT image acquisition [120 kVp; 2.5 mm Al inherent filtration +5.1 mm Cu added filtration; 2 mAs per projection (14.8 mGy air kerma per projection at the detector); 320 projections; 360° circular orbit with uniform projection weighting; SAD=93.5 cm; SDD=144.4 cm].

Term	Definition	Nominal value
Tj	Transfer function for stage j	—
Si	Noise-power spectrum at stage j	—
${\overline{q}}_o$	Mean fluence incident on the detector for a given projection	3.24×104 mm−2
${\overline{g}}_1$	Mean fraction of incident photons interacting with the detector	0.48
${\overline{g}}_2$	Mean number of optical photons produced per incident photon, including k-shell interactions	2850
Pk	Transfer function associated with k-fluorescence	—
T3	Transfer function due to spread of optical photons	—
${\overline{g}}_4$	Coupling efficiency of photodiode	0.6
apd	Width of (square) photodiode	0.32 mm
T5	Transfer function due to photodiode aperture	—
ai	Detector sampling interval in direction i	0.4 mm
III	Sampling function (comb, or Shaw function)	—
σadd	Additive electronics noise	3975 e∕pixel
Ai	Width of binning aperture (in pixels) in direction i	1
Bi	Downsampling factor in direction i	1
T8	Transfer function due to 2D binning aperture	—
T10	Ramp filter	—
T11	Apodization filter	—
hwin	Smoothing parameter	0.5
T12	Interpolation filter	—
m	Number of projections acquired across circular orbit	320
M	Magnification factor, SDD∕SAD	1.54
T13	Transfer function associated with back-projection	—
Θ13	Transfer function associated with back-projection of noise	—
bi	3D sampling interval in direction i	0.259 mm