A new functional medical imaging technique based on the detection in coincidence of threeγ-rays is being developed at Subatech laboratory. The goal of this innovative medical imaging modality is to obtain a precise 3D location of a radioactive source with high sensitivity, significantly reducing the dose administered to the patient. To exploit the benefits of this technique a new detection device, based on a liquid xenon Compton telescope with good spatial and energy resolutions, and a specific
(β+,γ) emitter radionuclide, ⁴⁴Sc, are required.
A first prototype of a liquid xenon time projection chamber named XEMIS1 has been successfully developed showing very promising results for the energy, spatial and angular resolutions of the ionization signal in liquid xenon. We achieve an energy resolution of 8.9% for a 1MeV γsource and an electric field of 1kV/cm, and a longitudinal spatial resolution smaller than 100μm. This first experimental device of small dimension count on an advanced cryogenics system, which has contributed to a high liquid xenon purity with a very good pressure and temperature stability, a fast UV sensitive PMT and an ultra-low noise front-end electronics (below 100 electrons) operating at liquid xenon temperature.
Based on the good results obtained with XEMIS1, a second prototype dedicated to small animal imaging, XEMIS2, is now under construction. This new prototype is a monolithic liquid xenon cylindrical camera, which totally surrounds the small animal. XEMIS2 will hold around 200kg of liquid xenon. The active volume of the detector will be completely covered by about 380 1" PMT to detect the VUV scintillation photons, allowing a pre-localization for the detection of the ionization signal and a reduction of the dead time. The ionization signals will be collected by around 20000 pixels. This innovative geometry will allow the detection of the threeγ-rays with a high sensitivity and a high Field-Of-View.
In parallel, a complete GATE/Geant4 simulation has been developed in order to understand the performances of the 3γimaging technique. The optimization of the geometry and electronics of XEMIS2 has been performed showing very promising results for the sensitivity, energy and spatial resolutions. Moreover, good quality preliminary images obtained by simulated tomographic reconstruction reveal the possibility of imaging the whole animal in a short time with a very low injected activity. These preliminary results are very promising for the consolidation of the 3γimaging technique and its future application in human body imaging.