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Simultaneous imaging of the SPECT tracer 131 I and PET tracer 18 F is important in the diagnosis of high- and low-grade thyroid cancers because high-grade thyroid cancers have high 18 F-FDG and low 131 I uptake, while low-grade thyroid cancers have high 131 I and low 18 F-FDG uptake. In this study, Na 131 I and 18 F-FDG were simultaneously imaged using the Compton-PET system, in vivo. The angular resolution and sensitivity of the Compton camera with 356 keV gamma ray measured using a 133 Ba point source were 12.3° and 2 × 10 -5 , respectively. The spatial resolution and sensitivity of PET were measured with a 22 Na point source. The transaxial and axial spatial resolutions of the PET at the center of the FOV were 1.15 mm and 2.04 mm, respectively. Its sensitivity was 1.2 × 10 -4 . In-vivo images of the 18 F and 131 I isotopes were simultaneously acquired from mice. These showed that 18 F-FDG was active in the heart, brown fat, and brain, while Na 131 I was active in the thyroid, stomach, and bladder. Artifacts were found in the Compton camera images when the activity of 131 I was much lower than that of 18 F. This study demonstrates the potential of simultaneous clinical imaging of 18 F and 131 I., (© 2024. The Author(s).)

In internal 131I therapy for thyroid cancer, a decision to continue treatment is made by comparing 131I scintigraphy and [18F]FDG-PET. However, with current SPECT and PET systems, simultaneous imaging of diagnostic PET nuclides and therapeutic 131I nuclides has not been achieved so far. Therefore, we demonstrated that the recently developed Compton PET hybrid camera with Ce:Gd3(Al,Ga)5O12 (GAGG)- Silicon Photomultiplier(SiPM) scintillation detectors can be used to simultaneously image 131I Compton image and 18F PET image., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)