Photon Factory Activity Report 2016 #34 (2017)

AR-NE7A/2016G004

Dual-Energy Pinhole-Type Fluorescent X-Ray Computed Tomography
for Scatter Correction
Tenta Sasaya1 Naoki Sunaguchi2 Thet-Thet-Lwin3 Kazuyuki Hyodo4
Tsutomu Zeniya5 Tohoru Takeda3 and Tetsuya Yuasa1,*
1
Yamagata University, Yonezawa 992-8510, Japan
2
Nagoya University, Nagoya 461-8673, Japan
Kitasato University, Sagamihara 252-0373, Japan
4
KEK, Tsukuba 305-0801, Japan
5
Hirosaki University, Hirosaki 036-8560, Japan
1 Introduction
We have so far proposed a pinhole-based FXCT (pFXCT) system with a 2-D detector and volumetric beam
[1]. This system enables faster data acquisition bycompletely eliminating the need for translational scans,and the first 3-D FXCT image of a physical phantom wasobtained using this system. However, the energy
resolution of the 2-D detector was not sufficiently high toenable discrimination between the fluorescent and strayscattered x-rays according to their energies. Even if thedetector was perpendicular to the incident beam so thatphotons scattered via Compton, Thomson, and multiple
scattering could be prevented from impinging upon thedetector, contamination was inevitable. Since all of thedetected x-ray photons were used in the reconstruction
and were treated as if they were fluorescent x-ray photons,
the background noise was enhanced, and the image
quality deteriorated. We propose a pinhole-based
fluorescent x-ray computed tomography (p-FXCT)
system with a 2-D detector and volumetric beam that cansuppress the quality deterioration caused by scattercomponents [2]. In the corresponding p-FXCT technique,projections are acquired at individual incident energies
just above and below the K-edge of the imaged traceelement; then, reconstruction is performed based on thetwo sets of projections using a maximum likelihood
expectation maximization algorithm (ML-EM algorithm)
that incorporates the scatter components.
2 Experiment
Figure 1 shows a schematic diagram of the proposed
imaging geometry. An incident monochromaticvolumetric beam, with photon fluxes parallel to one
another are linearly polarized within a horizontal plane,
impinging and covering the object. Imaging agents, suchas iodine, are thus excited and isotropically emit x-ray
fluorescent photons on de-excitation [3,4]. A thin W platewith a pinhole is placed between the object and the CCD
camera, such that the plate surface and the detective
surface are parallel to the beam propagation. Only
fluorescent photons passing through the pinhole aredetected by the 2D detector without energy resolution.
The projections are acquired just above and below the Kedge energy (33.4 and 33.0 keV). The procedure isrepeated while rotating the object over 180 degrees.

Fig. 1 Schematic diagram of the p-FXCT geometry(a)(b)
Fig. 2 (a) Simple subtraction, and (b) the proposed method.
3 Result
We imaged a 10-mm-diameter acrylic cylinder having
three 3-mm-diameter channels which were filled with I
solution of three kinds of concentration (0.1, 0.2, and 0.3
I mg/ml). Figure 2(a) and (b) are the reconstructed crosssections of the phantom obtained using simple subtraction,i.e., subtraction of the reconstructed image below the Kedge from one above the K-edge, and the proposed
method based on the ML-EM algorithm, respectively. The
back ground noise was removed and the contrast wasimproved using the proposed method.
References[1] N. Sunaguchi, et al, Opt. Comm. 297, 210 (2013).
[2] T. Sasaya et al, Sci. Rep. 7, 44143 (2017).
[3] T. Yuasa et al., IEEE trans Nul. Sci. 44, 54 (1997).
[4] Q. Huo et al., Opt. Lett. 33, 2494 (2008).
*yuasa@yz.yamagata-u.ac.jp