Demonstration of in-vivo simultaneous 3D imaging with ¹⁸F-FDG and Na¹³¹I using Compton-PET system

Simultaneous imaging of the SPECT tracer ¹³¹I and PET tracer ¹⁸F is important in the diagnosis of high- and low-grade thyroid cancers because high-grade thyroid cancers have high ¹⁸F-FDG and low ¹³¹I uptake, while low-grade thyroid cancers have high ¹³¹I and low ¹⁸F-FDG uptake. In this study, Na¹³¹I and ¹⁸F-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 ¹³³Ba point source were 12.3° and 2 × 10^-5, respectively. The spatial resolution and sensitivity of PET were measured with a ²²Na 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 ¹⁸F and ¹³¹I isotopes were simultaneously acquired from mice. These showed that ¹⁸F-FDG was active in the heart, brown fat, and brain, while Na¹³¹I was active in the thyroid, stomach, and bladder. Artifacts were found in the Compton camera images when the activity of ¹³¹I was much lower than that of ¹⁸F. This study demonstrates the potential of simultaneous clinical imaging of ¹⁸F and ¹³¹I.