(A) study on application of monochromatic dual energy CT algorithm to polychromatic energy and its acceleration

Abstract

Micro CT has been used widely in research fields of specimens and small animals for its ability of non-destructive or in vivo imaging. Micro CT with dual energy options has become particulary important in the preclinical studies such as obesity. In this study a simple post-reconstruction dual energy CT method is proposed. A dual energy CT algo-rithm for monochromatic x-rays was adopted and applied to the dual energy CT of poly-chromatic x-rays. The algorithm for monochromatic x-rays was implemented and tested with a mathematical phantom. In order to test the sensitivity of this algorithm to errors of x-ray energies values a simulation study was performed with the mathematical phantom. To represent a polychromatic x-ray energy spectrum with a single energy, mean energy of the normalized spectrum and equivalent energy were used as representative energy of polychromatic x-ray. The proposed method was experimentally tested with two different micro CT scanners and a test phantom made of PMMA, water and graphite. CT scans were taken at 40 $kV_{p}$, 50 $kV_{p}$, 60 $kV_{p}$, 70 $kV_{p}$ and 80 $kV_{p}$ of energy. The dual energy calculations to extract the effective atomic number ($Z_\it{eff}$) and the electron density information of the phantom materials were carried out with CT images of all energy pairs. The effective atomic number and the electron density values obtained from the proposed method were compared with the theoretical values. The results showed that, using the mean energy to represent a polychromatic spectrum, errors less than 6.0 % in the extracted values can be achieved. Computation acceleration techniques, such as OpenMP and CUDA, were used for fast computation. These techniques reduced computation timeup to a few hundred times. The proposed method showed the simplicity of calculation, practicality and thus the feasibility to use with a general polychromatic CT.