Abstract
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Objectives: Therapeutic nuclide distribution is important to evaluate the anti-tumor effect, and the comparison with the diagnostic images is needed to improve theranostics. However, diagnostic and therapeutic imaging are performed separately because the specifications in the current modalities are limited. Superimposition of two different images has been developed, but such processes cannnot avoid misalignment with a millimeter unit and changes in the shape of the tumor due to time interval. For this reason, imaging device which can obtain images for each nuclide on the same coordinates is needed to compare two nuclides’ distributions. Compton camera potentially can obtain γ-rays with different energies. Furthermore, when the camera is combined with PET, it can take full advantages of well-established PET technology. Therefore, we developed the Compton-PET hybrid camera which can image single gamma ray as well as annihilation radiation emitted from diagnostic and therapeutic nuclides.
Methods: The Compton-PET hybrid camera is composed of a pair of Compton cameras arranged 180 degrees from each other. One Compton camera includes a scatterer detector, inducing Compton scatter, and an absorber detector that measures scattered γ-rays. The scatterer detector is composed of 8×8 array of 2.5×2.5×1.5 mm3 GAGG and SiPM. The absorber detector is composed of 8×8 array of 2.5×2.5×10 mm3 GAGG and SiPM, and is also used as PET scanner . In this experiment, 18F was used as a diagnostic nuclide and 131I was used as a therapeutic nuclide which emits both of γ-rays and β-rays simultaneously. PET image and γ-rays image with optimized energy window (511 keV ±10 %, 364 keV ±10 %, respectively) were simultaneously acquired from the same list mode data. Set up of the measurement targets is shown in Figure 1.
Results: PET images shows in Figure 2, in which only 18F is depicted. Compton images for γ-rays and for annihilation radiation are shown in Figure 3 and 4, respectively. Only 131I in Figure 3 and only 18F in Figure 4 are depicted.
Conclusions: We developed the Compton-PET hybrid camera enable for imaging each nuclide under different nuclides existing, and succeeded in imaging by switching Compton-mode and PET-mode with optimized energy windows. This camera is potentially helpful to evaluate the accumulation of diagnostic and therapeutic nuclides at the same time.