Photon Factory Activity Report 2017 #35 (2018)

AR-NE7A/2016G004

X-Ray Fluorescence Computed Tomography Imaging of Gold Nanoparticles
Tenta Sasaya 1, Seung-Jun Seo 2, Naoki Sunaguchi 3, Tsutomu Zeniya 4,Kazuyuki Hyodo 5, Jong-Ki Kim 2, and Tetsuya Yuasa 1,*
1

Yamagata University, 2 Catholic University of Daegu,
3
Nagoya University, 4 Hirosaki University, 5 KEKGold nanoparticles (GNPs) have attracted attention in
nanomedicine as novel contrast agents for cancer
imaging. They can selectively accumulate within a tumorand remain there for longer durations compared toconventional iodinate contrast agents. Their specificity
can be increased through the active targeting achieved byconjugation with antibodies or peptides directed against
tumors. In addition to the active specific tumor targetingand slower clearance, they offer a noteworthy advantagethat they have been shown to enhance the local dose
deposition for x-ray radiotherapy. For cancer diagnosis,planning, and treatment, it is very important to develop atool to identify, quantify, and locate GNPs distributed in abiological object. In this study, we proposed atomographic imaging method to visualize thedistribution of NPs with a spatial resolution of submillimeters using x-ray fluorescence emitted from theNPs, and constructed a prototype x-ray fluorescencecomputed tomography (XFCT) system usingsynchrotron radiation as an incident beam. This report
describes the imaging principle of XFCT from theviewpoint of measurement science, and shows somepreliminarily experimental results for demonstrating
the efficacy.
We constructed the XFCT imaging system at thebending-magnet beamline AR-NE7A in KEK. A
PILATUS 100K manufactured by DECTRIS Ltd. wasused. In this study, we paid attention to the L-shell
fluorescence of Au (L: 9.71 keV, L: 11.4 keV)because the quantum efficiency at energies around 10keV is approximately 90%, and the photoelectric crosssection at incident energies around the L-edge of Au isapproximately 20 times higher than that around the Kedge. We used the monochromator to select an incident
energy of 25 keV, which was the minimum energy set
in the beamline, so that the incident energy was asclose as possible to the L-edge energy of Au within theallowable range to produce more L-shell fluorescencephotons. The flux was approximately 5.0108
photons/mm2/s in front of the object. The cross sectionof the incident beam was collimated to 35 mm(horizontal)  5 mm (vertical) by the slit. The distance
between the rotational axis and the collimator plane
was 27.5 mm, and the distance between the collimatorplane and the detector surface was 30.0 mm. The
rotational stage and the detector were controlled by aPC. We imaged a physical phantom consisted of a 10mm-diameter PMMA cylinder with three 3-mmdiameter channels filled with GNPs solution ofFig. 1 Physical phantom: The photograph (left) andthe cross section (right).

3mm

3mm

Fig. 2 Reconstructed image: The cross sectional image(left), the 3-D volume rendering image (right).

different concentrations (1.0, 2.0, and 4.0 Au mg/ml),
as shown in Fig. 1.
Fig. 2 shows the cross sections at the central level ofthe 3-D reconstructed image of the phantom and theimage in the volume rendering (VR) representation.
While the Au regions are distorted in the VR image,the distortion mainly was caused by theinhomogeneous distribution of intensity in the incident
beam. Analysis of the image revealed that the spatial
resolution was about 0.3 mm, and the imaging method
enabled highly quantifiable measurement. We obtained
a satisfactory 3-D reconstructed image. We areplanning ex-vivo imaging of rat’s brain and heart innear future.
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).
4. T. Sasaya et al., Nucl. Inst. Meth. A 886, 71 (2018).
*yuasa@yz.yamagata-u.ac.jp