1. Lei Li, Linyuan Wang, Ailong Cai, Xiaoqi Xi, Bin Yan, Shanglian Bao
A Fast and Accurate Projection Decomposition Algorithm for Dual-Energy CT Based on Isotransimission Curve Fitting
Lei Li, Linyuan Wang, Ailong Cai, Xiaoqi Xi, Bin Yan, Shanglian Bao
National Digital Switching System Engineering and Technological Research Center
Abstract
Dual Computed Tomography (DECT) has been a research hotspot in imaging field recently because its ability object separation, contrast enhancement, artifact reduction material composition assessment. fast accurate projection decomposition algorithm based isotransmission curve fitting DECT is proposed this paper. Firstly, single variable nonlinear problem given polychromatic value. is converted into a regional analytical solution with high accuracy by Taylor series expansion. Secondly, quadratic polynomial model respectively built low energy Finally, the joint nonlinear solving problem transformed into curves intersection problem. Experiment results show that compared to matching method, precision speed method are increased by ten times at least four respectively, noise fluctuation image reconstruction reduced 25%. Keywords: dual computed tomography; decomposition; isotransimission curve; Taylor’s series expansion.
Results
The ideal X-ray energy spectrum is simulated by SpekCalc software. The simulated normalized energy spectrum is shown in Fig.1.
A numerical phantom with bone and water is established as shown in Fig.2(a).
The projection decomposition results are shown in Fig.3.
The projection decomposition results of the two methods are separately used for reconstruction and we have the distribution image of the basis material. The reconstruction results are shown in Fig. 4.
Method
In X-ray imaging systems, energy spectra generated by X-ray sources are polychromatic. Consider the general form of basis effect decomposition model and basis material decomposition model as： 
Therefore, the meaning of the above decomposition model is that when basis functions f1 and f2 are known, the accurate solution can be converted into the solution for the decomposition efficient c1 and c2.
Under high and low energy spectra settings, high and low projection pH and pL can be expressed with projection decomposition model by:
where SH and SL refer to normalized high and low energy spectra. C1 and C2 are the line integrals along the ray path. The basic principle of DECT pre-processing reconstruction in projection domain is that based on the above decomposition model, pH and pL acquired at different views are utilized to solve the line integral 1 C and 2C . It is called the process of projection decomposition.