Affiliations: Department of Engineering Physics, Tsinghua
University, Ministry of Education, Beijing, China | Key Laboratory of Particle and Radiation Imaging,
Tsinghua University, Ministry of Education, Beijing, China
Note: [] Corresponding author: Liang Li, Department of Engineering
Physics, Tsinghua University, Key Laboratory of Particle and Radiation Imaging
(Tsinghua University), Ministry of Education, Beijing 100084, China. Tel.: +86
10 6278 5142; E-mail: liliang02@mails.tsinghua.edu.cn
Abstract: With its capability of material discrimination, dual energy computed
tomography (DECT) is widely used in security inspection for the purpose of
detecting contraband. DECT provides effective atomic number image and electron
density image in addition to traditional attenuation images. In dual energy
liquid inspection system, the presence of metallic containers will cause
partial volume effect (PVE) that leads to severe deviation in effective atomic
number image. Usually, the deviation is too large for a reliable material
discrimination and may cause false results. In this paper, a projection
splitting method is proposed to combat the PVE. This method is based on the
assumption that a prior projection of the empty container is available and
photoelectric and Compton coefficient integrals can be calculated via dual
energy decomposition. Each integral is split into two parts by subtracting the
integral of the empty container from the total integral. The subtraction
removes the integral part contributed by the container, thus discarding the
error source created by PVE that appears on the boundary of the sinogram.
Images are reconstructed in which only the interior liquid area remains.
Experiments are performed in a real liquid inspection system to demonstrate the
effectiveness of this method. Accuracy of the reconstructed effective atomic
number is greatly improved with this method, which helps a lot in
determining the type of the object.
Keywords: DECT, partial volume effect, liquid inspection, effective atomic number
