This page describes an application for two-step spectral CT reconstruction. Please start by reading the general documentation on spectral CT.
RTK provides a command line application to simulate the measured projections in spectral CT from the decomposed projections, the incident spectrum, the material attenuations and the detector response. It is the "forward operator" in the inverse problem that RTK solves to obtain the decomposed projections from the measured projections.
The data used in this documentation page can be downloaded using Girder. It is a simulation through a cylinder of water with two inserts, one empty, the other filled with cortical bone.
# Simulate the measured projections (photon counts on the spectral detector)
# from the decomposed projections, the incident spectrum,
# the material attenuations and the detector response.
rtkspectralforwardmodel \
-o cl_counts.mha \
-i decomposed.mha \
-d drm.mha \
--incident no_vector_spectrum.mha \
-a mat_basis.mha \
-t 20,40,60,80,100
cl_counts.mha should be identical to counts.mha. You can check it with VV using the overlay feature.