
References 427
the same for all the rays in the projection data, which is usually not the case.
A more general expression (not using this assumption) for the noise variance
was derived by Kak [34] who has also introduced the concept of the relative-
uncertainty image.
The algebraic approaches to image reconstruction have been studied in
great detail by Gordon et al [22-25], Herman et al [27, 29] and Budinger
and Gullberg [10]. To somewhat improve the noise properties of the alge-
braic techniques, a simultaneous iterative reconstruction technique was
proposed by Gilbert [21].
The reconstruction implementations that we presented in this chapte ...