Photon Factory Activity Report 2018 #36 (2019)

AR-NE7A/2018G004

Multi-Pinhole Based X-Ray Fluorescence Computed Tomography: ImagingExperiments
Using Rat HeadPhantoms
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Keishi Araki Koki Kato Tsuyoshi Oouchi Tenta Sasaya Seung-Jun Seo
Naoki Sunaguchi3 Kazuyuki Hyodo4 Tsutomu Zeniya5 Jong-Ki Kim2 and Tetsuya Yuasa1,*
1
Yamagata University, Yonezawa 992-8510, Japan
2
Catholic University of Daegu, Daegu 705-034, Korea
3
Nagoya University, Nagoya 461-8673, Japan
4KEK, Tsukuba 305-0801, Japan
5Hirosaki University, Hirosaki 036-8560, Japan
1 Introduction
Multi-pinhole based x-ray fluorescence computed
tomography (mp-XFCT) delineates the spatial distributionof the non-radioactive agent in a living body by using
fluorescent x-ray photons [1-3], which are emitted from theagent on de-excitation soon after extrinsic excitation andacquired with a multi-pinhole collimator and a 2-D
detector. One of the potential applications is to image brainof small animals for development of treatment techniques
and new drugs of brain disease in preclinical study.
However, the measured photons are limited because a brain
is covered with a skull which is a highly absorbing object.
In this research, in order to investigate the applicability tobrain imaging, we performed imaging experiments withphantoms to simulate a rat head using an actual mp-XFCT
system, constructed at beamline AR-NE7A in KEK (Fig.1).
2 Experiment
We imaged two kinds of physical phantoms imitating
rat’s head. One was an acrylic (PMMA) cylinder with 15
mm in diameter and 40 mm in height, which was covered
with Al with 1 mm in thickness. It had three cavities with
3 mm in diameter and 15 mm in depth, which were filledwith different concentration of I. The other was a rat skull
including an I solution in the cerebral ventricle. The acrylic
phantom and the rat skull phantom were rotated at anangular step of 2° and 4° over 360°, respectively. The
measurement time per projection were 180 s and 60 s forthe acrylic phantom and for the rat skull phantom,respectively. Namely, the number of projections for theformer and for the latter were 180 and 90, respectively.
Each phantom was measured two times while changing theconcentration of I.

(a)

(b)

Fig. 2: Reconstructed images of the acrylic phantom.

(a)

(b)

Fig. 3: Reconstructed images of the rat skull phantom in
MIP representation.
3 Results and Discussion
Figures 2(a) and (b) are a cross section of thereconstructed image of the acrylic phantom; The former
had an I solution of relatively higher concentration than thelatter. Although the concentration higher than 0.2 mg/ml
was depicted, the concentration less or equal to 0.1 mg/ml
could not be detected. The results show that the limit ofdetection of this phantom is 0.2 mg/ml. Figures 3(a) and(b) are reconstructed images of the rat skull phantom in
MIP (Maximum Intensity Projection) representation; The
former and the latter had I solution of 0.4 mg/ml and 0.2mg/ml, respectively. In the both cases, the iodine regions
are satisfactorily reconstructed. From the results, the iodine
regions are satisfactorily reconstructed by mp-XFCT even
if they are covered with a highly absorbing object,
although the limit of detection decreases compared to thecase without a highly absorbing cover.
References[1] T. Yuasa et al., IEEE Trans. Nucl. Sci. 44, 54 (1997).
[2] T. Sasaya et al., Sci. Rep. 7, 22143 (2017).
[3] T. Sasaya et al., Sci. Rep. 7, 5742 (2017).

Fig. 1: Schematic of mp-XFCT

Research Achievements
1. T. Sasaya et al., LNCS 10884, 205 (2018).
* yuasa@yz.yamagata-u.ac.jp