  X-ray fluorescence computed tomography based on sheet-beam can save a huge
amount of time to obtain a whole set of projections using synchrotron. However,
it is clearly unpractical for most biomedical research laboratories. In this
paper, polychromatic X-ray fluorescence computed tomography with sheet-beam
geometry is tested by Monte Carlo simulation. First, two phantoms (A and B)
filled with PMMA are used to simulate imaging process through GEANT 4. Phantom
A contains several GNP-loaded regions with the same size (10 mm) in height and
diameter but different Au weight concentration ranging from 0.3% to 1.8%.
Phantom B contains twelve GNP-loaded regions with the same Au weight
concentration (1.6%) but different diameter ranging from 1mm to 9mm. Second,
discretized presentation of imaging model is established to reconstruct more
accurate XFCT images. Third, XFCT images of phantom A and B are reconstructed
by fliter backprojection (FBP) and maximum likelihood expectation maximization
(MLEM) with and without correction, respectively. Contrast to noise ratio (CNR)
is calculated to evaluate all the reconstructed images. Our results show that
it is feasible for sheet-beam XFCT system based on polychromatic X-ray source
and the discretized imaging model can be used to reconstruct more accurate
images.
