Table 1.

Parameter definition for the 2D fan-beam CT geometry (FOV denotes the field of region within the attenuation object).

O, Q	isocenter of FOV and X-ray source	θ⃗	unit ray directional vector
y⃗(β)	circular trajectory of Q	X	coordinate position
β	projection view	rϕ	radial distance between X to O
γ	fan angle	ϕ	directional angle of rϕ
R	source-to-isocenter distance	Rv	radial distance between M (N) to O
θm	angle range of the discrete S-curves	ϕ0	directional angles of $\overrightarrow{OP}$
P	middle point of $\overrightarrow{MN}$	ϕ1	directional angles of $\overrightarrow{ON}$
M, N	points linking the boundary of FOV	ϕ2	directional angles of $\overrightarrow{OM}$