There is a constant push to reduce both the radioactive dose injected into the patient and the duration
of a PET scan. Achieving these and providing real-time images require a new imager principle. 3-photon
gamma imaging is such a technique. Simulations of a small prototype, called XEMIS (Xenon Medical
Imaging System) showed the additional information helps localize the nuclear disintegrations.
Improvements are needed to scan a human body. In XEMIS, nuclear disintegrations necessitate two
data acquisition chains. One of them needs a new design to cater for a larger number of light detectors.
Determining which Events are in coincidence necessitates a specific hardware data processing ensure
Real-time imaging. Finally, new image reconstruction algorithms are required to take the third photon
into account. RETIREX aims at providing the key elements necessary to build the future whole-body 3-
photon imager. 

To address these, the RETIREX project is gathering 4 partners: IMT Atlantique (LabSTICC ARCAD and Subatech), LaTIM and UBS, each with the necessary skills to improve XEMIS, Fig1.

Fig. 1: Project’s workpackages and partners.

A first XEMIS prototype, designed by Subatech, Fig .2, is being assembled at Nantes’ University Hospital, Fig 3.

Fig. 2: XEMIS2 prototype is designed to scan small animals.
Fig. 2: XEMIS2 prototype being assembled at Nantes’ University Hospital.

Visit Xemis 2 | IMT Atlantique ( for more information about XEMIS2.

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