The XEMIS project (XEnon Medical Imaging System) initiated by SUBATECH proposes a new nuclear imaging modality based on the detection in coincidence of 3γ rays. The main profit of this medical imaging technique called 3γ imaging is the significant reduction of the injected dose. A first prototype XEMIS1 has successfully shown the concept feasibility. A second device XEMIS2 dedicated to carry out small animal imaging will be ready to use this year after several tests. The enhancement of the amount of Xenon between XEMIS1 and XEMIS2 has required a careful reconsideration of the cryogenic processes.
XEMIS2 is based on a Time Projection Chamber (TPC) filled with pure liquid Xenon only during the medical exam. Used in a closed loop, the fluid is purified and liquefied permanently. The limited thickness of XEMIS2 cryostat makes the TPC a low pressure vessel (< 2 bar abs) incompatible with a long term cryogenic storage. For all these reasons, a purification device, condenser, reversible transferring system, safe tank storage (able to disconnect from the TPC) are necessary. A deported high-pressure proof subsystem called ReStoX (Recovery and Storage of Xenon) gathers the three last elements. Its modular cold duty allows it to bring and maintain the Xenon into the right pressure and temperature thanks to the adjustable boil-off condensation. That feature explains why ReStoX constitutes by itself the Xenon liquefaction site, the distribution and recovering device. It combines the essential cryogenic processes implemented and soon tested for this new 3γ medical imaging.