XEMIS2: A liquid xenon detector for small animal medical imaging

Highlights: • The first 3 gamma whole-body small animal scanner is presented. • The XEMIS2 camera is a single-phase liquid xenon detector with a 24 cm axial field of view. • A dedicated 32-channels low power circuit called XTRACT is described. • ReStoX is an advanced cryogenic system developed to liquefy, recover and store the xenon. • A reconstructed image using the innovative 3 gamma reconstruction algorithm is reported. We report a new liquid xenon Compton camera, called XEMIS2 (XEnon Medical Imaging System), developed to image for the first time small animals using $3\gamma$ imaging. This technique proposes an alternative to reduce the administered radiopharmaceutical activity while preserving diagnostic image quality using liquid xenon as detection medium. Given the success of its predecessor, a small dimension liquid xenon time projection chamber called XEMIS1, we are currently building a larger scale detector for preclinical applications. This second prototype, XEMIS2, is a single phase liquid xenon cylindrical camera with a large axial field of view for full-body small animal imaging. XEMIS2 holds around 200 kg of xenon and it has been designed to enable high-efficiency and simultaneous detection of the three $\gamma$-rays emitted by a ⁴⁴Sc radionuclide. The innovative geometry of XEMIS2 will allow to discriminate and measure the position and deposited energy of most Compton interactions inside the detector. In order to manage such a large quantity of xenon, an innovative high-pressure subsystem known as ReStoX has been developed and successfully qualified. ReStoX allows to maintain the xenon in liquid state at the desired temperature and pressure, transfer the xenon into XEMIS2 and store it during long term periods. XEMIS2 will be installed at a non controlled radioactive area of Nantes Hospital. The goal is to evaluate image quality of a 20 min whole-body preclinical exam with an injected activity of 20 kBq.