Simultaneous X-Rays/optical tomography of small animals

A small animal multimodality tomographer dedicated to the co-registration of fluorescence optical signal and X-rays measurements has been developed in our laboratory. The purpose of such a system is to offer the possibility to get in vivo anatomical and functional information at once. Moreover, anatomical measurements can be used as a regularization factor in order to get the reconstructions of the biodistribution of fluorochromes more accurate and to speed up the treatment. The optical system is basically composed with a CW laser (Krypton, 752 nn) for an optimal excitation of Alexa-Fluor 750 fluorochromes, and a CCD camera coupled with a combination of filters for the fluorescence detection. The animal is placed inside a transparent tube filled with an index matching fluid. In order to perform multiple views of fluorescence data acquisitions, the cylinder is fixed to a rotating stage. The excitation beam is brought to the cylinder via two mirrors mounted on translation plates allowing a vertical scan. The optical data acquisitions are performed with a high sensitivity CCD camera. The X-ray generator and the X-ray detector have been placed perpendicularly to the optical chain. A first study on phantoms was conducted to evaluate the feasibility, to test the linearity and the reproducibility, and to fix the parameters for the co-registration. These test experiments were reproduced by considering mice in the oesophagus of which thin glass tubes containing fluorochromes were inserted. Finally, the performance of the system was evaluated in vivo on mice bearing tumours in the lungs, tagged with Transferin-AlexaFluor 750.