I am using rtkfdk.exe to generate 3D image by using measured input projections (0-360 degree) and the Geometry.xml file. I would like to extract the attenuation matrix (Ax=p) where x is the 3D image matrix and p is a 3D matrix of 2D projections at different angles. I would greatly appreciate it if anyone can let me know how to proceed. I can also generate the 3D image by using rtkramp.exe then performing rtkbackprojections.exe on the output of rtkramp.exe.
Thanks @dzenanz for forwarding the message. I would call it the system matrix or the projection matrix. In general, RTK does not store it but computes it on-the-fly, mainly because it’s generally too large for CT. But we have implemented this and we use it for small test cases. It only works for 2D and one projection operator, JosephForwardProjectionImageFilter. The command line tool is rtkprojectionmatrix and you need to pass the same parameters as what you’d use to generate data files for the phantom. It stores it in a Matlab file format but it can be read from python too. RTK does not know how to use it because it can compute it on-the-fly.
I hope it will work, I haven’t used it in a long time…