X-ray spectrum estimation from transmission measurements using the expectation maximization method

X-ray spectrum estimation remains an active research area for its importance in medical imaging applications such as dose calculation and beam-hardening correction. In this paper, spectrum estimation is posed as an image reconstruction problem and the classical expectation maximization method (EM) for emission computed tomography is used to reconstruct the spectrum from transmission data. And we propose to compute the initial value for the EM iteration using Monte Carlo calculations. Numerical simulations were carried out to test the accuracy and robustness of the method. Experiments were conducted on an experimental CT system to evaluate the practicability of the algorithm. Both the simulations and experiments show that the proposed method can always produce a spectrum which fits the transmission data accurately and exhibits a rational shape.