3$\gamma $ Medical Imaging with a Liquid Xenon Compton Camera and $^{44}$Sc Radionuclide

The development of a liquid xenon Compton camera called XEMIS2 ( XEnon Medical Imaging System) is a step forward to a new type of medical imaging based on the use of Sc-44 radionuclide emitting two annihilation gamma rays and a third high energy gamma ray simultaneously. The single phase TPC (Time Projection Chamber) under construction, containing nearly 200 kg of xenon, is designed to measure most of the Compton interactions in the active area with a sub-millimetre position resolution and a good energy resolution of 4% on 511 keV photopeak. The intersection of the Compton cone surface from the third gamma ray with the line of response from the two annihilation gamma rays allows to localize the radionuclide with a precision (FWHM) of about 1 cm along this line. The large field of view of such a liquid xenon camera combined with the 3 gamma imaging technique will provide a good quality image while keeping the injected activity at a very low level. XEMIS2 will be installed in the Nantes University Hospital in order to demonstrate its capability to image small animals injected with a low activity of only 20 kBq in 20 mn acquisition time. To achieve this goal, a precise measurement of the ionization signal is provided by a pixelized anode, shielded by a Frisch Grid and read out by a low noise front-end electronics. In addition, new cryogenic and purification subsystems have been tested, allowing safe recovery of xenon in liquid phase at flow rates of about 1 ton per hour.