Validation of Fluorescence Molecular Tomography/Micro-CT Multimodal Imaging In Vivo in Rats

Rats are important preclinical models for studying breast cancer metastasis and bone pathologies. In these research areas, fluorescence molecular tomography (FMT) is commonly applied for quantitative three-dimensional (3D) imaging in mice. However, uncertainties due to strong depth dependency of FMT signal and spatial resolution require a validation study in rats. FMT performance in rats was assessed based on co-registered FMT/micro-computed tomography (micro-CT) reconstructed volumes obtained from optical phantoms and from models relevant for tumor imaging, bone remodeling and biodistribution analysis of nanoparticles. FMT reconstructions within 20-mm-thick optical phantoms were accurate (95 +/- 11 % recovery), precise (CV a parts per thousand currency signaEuro parts per thousand 8 %) and linear (R (2) > 0.9788) over a range of 78-2,500 nM of the near infrared fluorescent agent VivoTag 750 (VT750). In vivo, implanted defined fluorescent targets yielded a recovery of 105 +/- 5 % and successfully co-registered with micro-CT delineated structures. Additionally, using the bone-targeting imaging agent Osteosense 750, regions of neo bone formation identified by FMT could be mapped to the region of epiphyseal growth plates observed in micro-CT images. Finally, as a proof of concept, to monitor nanoparticulate drug pharmacokinetics in rat subjects the accumulation/clearance of VT750-albumin conjugate in/from the liver was followed at 11 different time points over a period of 2 weeks by FMT/micro-CT. FMT imaging has been validated in optical phantoms as well as in 160 g rats, and sequential FMT/micro-CT imaging can be considered as a useful tool for preclinical research in rats.