Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Progress on double photon coincidence imaging with 67 Cu and 169 Yb
K. Shimazoe,∗1 M. Uenomachi,∗2 H. Takahashi,∗1 Y. Shigekawa,∗3 A. Nambu,∗3 X. Yin,∗3 and H. Haba∗3
In nuclear medical imaging, positron emission tomography (PET) and single photon emission computed tomography (SPECT) are two important imaging modalities; however, the imaging principles of these modalities
have remained the same for more than 50 years. We haveproposed and investigated a novel imaging method referred to as double photon emission coincidence imaging(DPECI) utilizing two successive gamma-rays emitted
from cascade nuclides.1,2) The coincidence detection of
two gamma-rays enables the localization of radioisotope
with a single event. Previous studies have shown theincrease in signal to noise ratio (SNR) and reduction ofcross-talks between nuclides through the application of
selection with timing information using 111 In and 177 Lu,
which are clinically used radioisotopes for diagnosis andtherapy.3,4) Furthermore, in addition to the conventional
accumulation imaging of radioisotope, the hyperﬁne interaction of intermediate state in cascade nuclides withthe external ﬁeld can be used to detect the chemical information using the successive gamma-ray photons asreported in previous studies.5,6)
Here we investigate the possible use of 67 Cu and 169 Yb
for DPECI with collimator-based imaging system. 67 Cu
and 169 Yb were produced in the 70 Zn(d, αn)67 Cu and169Tm(d, 2n)169 Yb reactions at the RIKEN AVF cyclotron. 67 Cu emits two gamma-rays with energies of91.3 and 93.3 keV with the time constant of 9.1 µs in acascade decay. 169 Yb also emits two gamma-rays withthe combination of 63.1–177 keV, 63.1–198 keV, and
63.1–307.7 keV in cascade decays and the time constantis approximately 659.9 ns. The relatively long intermediate time constant could be useful to detect the hyperﬁneinteraction through the gamma-ray distribution. In thisstudy, we demonstrate DPECI method using the combination of slit and parallel-hole collimators achieving
higher sensitivity than parallel-hole only collimators using 67 Cu.7)
Figure 1 shows the experimental setup of DPECI to visualize 67 Cu radioisotope using the coincidence detectionof two gamma-rays. 67 Cu with the activity of 2.12 MBq
was enclosed in the U-shape phantom and measured for
16 hours. The time window was set to 10 µs. The shapeof U is successfully visualized by considering the intersection of a plane determined by slit collimators anda line by parallel-hole collimators. The slit width ofcollimator was 1.6 mm with thickness of 15 mm. The
gamma-rays were detected by 2.5 mm × 2.5 mm × 4 mm
(D) HR-GAGG scintillation crystals arrays coupled toSiPM arrays.
For evaluating the feasibility of coincidence detection of two successive gamma-rays from 169 Yb, ring∗1∗2∗3

School of Engineering, University of Tokyo
Unit of Synergetic Studies for Space, Kyoto University
RIKEN Nishina CenterFig. 1. Geometry of DPECI for visualizing 67 Cu radioisotope
enclosed in U shape phantom and its image.

shape GAGG-SiPM detector arrays including 512 channels were used. The left panel in Fig. 2 shows the time
diﬀerence between two gamma-rays and the decay time
constant of 659.9 ns is successfully observed. The rightpanel shows the energy spectrum obtained from the timeover-threshold (ToT) measurement, which indicates thatthe gamma ray energy is correctly identiﬁed.

Fig. 2. Coincidence time histogram of two gamma-rays from169
Yb and the measured energy spectra with GAGGSiPM arrays.

In summary, we have proposed a new method(DPECI) using double photon emitting nuclides and theimaging capability and coincidence detection was demonstrated with 67 Cu and 169 Yb fabricated at RIKEN AVF
cyclotron.
References
1) K. Shimazoe et al., J. Instrum. 12, C12055 (2017).
2) M. Uenomachi et al., Bull. Am. Meteorol. Soc. 18, 120(2022).
3) M. Uenomachi et al., Sci. Rep. 11, 13330 (2021).
4) M. Uenomachi et al., J. Instrum. 17, P04001 (2022).
5) K. Shimazoe et al., Commun. Phys. 5, 1 (2022).
6) K. Shimazoe et al., Bull. Am. Meteorol. Soc. 18, 127(2022).
7) L. Yan et al., Nucl. Instrum. Methods Phys. Res. A 1053,168305 (2023).

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