% CT data
% For CT data, only the class based functionality is supported. Examples are 
% available in |walnut2D_CT_main.m|, |walnut_CT_main.m| and |Inveon_CT_main.m|, 
% where the first one is a pure 2D (fan-beam) example while the latter  two are 
% 3D (cone-beam) examples (it is possible to convert the latter  two to 2D as 
% well). In all cases, it is assumed that the source is  initially at the bottom 
% of the image and rotates counter-clockwise.
% 
% There are three different ways to construct the cl