Ponente
Descripción
Hybrid imaging systems integrating Positron Emission Tomography (PET), Magnetic Resonance Imaging (MRI), and Focused Ultrasound (FUS) are increasingly demanded in preclinical and translational research, yet no trimodal commercial solution currently exists. We have designed, assembled, and validated a dedicated PET insert based on monolithic LYSO crystals (33×25.4×8 mm³) with 67 mm of axial FOV, capable of simultaneous operation with high-field MRI and commercial FUS devices. We evaluated the system inspired on NEMA NU-4 2008 protocol. The PET insert achieved a homogeneous submillimeter resolution (0.9 mm with Depth of Interaction), a sensitivity of 3.8%, and a Noise Equivalent Count Rate peak of 80 kcps. Image quality metrics yielded recovery coefficients up to 0.89 and spill-over ratios of 11% (air) and 22% (water), matching state-of-the-art preclinical PET scanners.
Beyond performance characterization, the PET insert was employed in various trimodal studies. In a proof-of-concept phantom experiment, the PET was combined with a custom low-field MRI and a custom FUS device. Localized sonication was used to heat up the phantom and melt a gelatin compartment, allowing the initially confined ¹⁸F-FDG solution to diffuse into the gel matrix. This redistribution process was successfully monitored in real time by PET-MRI.
Subsequently, in vivo feasibility was demonstrated in murine brain studies using our PET insert combined with a 9.4T MRI and a commercial RK-300 FUS system. FUS-induced BBB opening was achieved with microbubbles, while Gd-DOTA (MRI) and ⁶⁴Cu-DOTA (PET) were co-administered. PET-MRI images confirmed co-localization of contrast enhancement with sonicated regions, validating the ability of the trimodal system to perform concurrent imaging and therapy monitoring in vivo.
In parallel, we investigated the impact of high magnetic fields on PET resolution through a positron range confinement study. A microDerenzo phantom was sequentially filled with ¹⁸F, ⁸⁹Zr, and ⁶⁸Ga and imaged with the PET insert inside and outside a 9.4T MRI. Results confirmed that the magnetic field confines positron trajectories perpendicular to B₀, with the most pronounced benefits for high-energy emitters: rods as small as 0.9 mm with ⁸⁹Zr and 1.0 mm with ⁶⁸Ga were resolved inside the MRI, while only the 1.2 mm and 1.5 mm rods were distinguished when the PET insert was outside the MRI, respectively.
These results establish the developed PET insert as the first preclinical trimodal PET-MRI-FUS platform, offering both state-of-the-art PET performance and unique multimodal capabilities. By enabling simultaneous imaging and therapy guidance, as well as demonstrating positron range confinement at 9.4T, this system opens new avenues for molecular imaging, BBB-targeted drug delivery, and advanced preclinical FUS research.
