
8.6
Reconstruction from Fan Projections
407
S
(c)
Fig. 27 While for the parallel-beam case the filtered projections are backprojected along
parallel lines (a), for the fan-beam case the backprojection is performed along converging lines (b).
(c).
This figure illustrates the implementation step that in order to determine the backprojected
value at pixel (x, y), one must first compute γ' for that pixel.
Although the projections are measured on a line such as in Fig. 28, for
theoretical purposes it is more efficient to assume the existence of an imagin-
ary detector line D\D'
2
passing through the origin. We associate the ray
integral along SB wit ...