  PETALO (Positron Emission Tof Apparatus with Liquid xenOn) is a novel concept
for positron emission tomography scanners, which uses liquid xenon as a
scintillation medium and silicon photomultipliers as a readout. The large
scintillation yield and the fast scintillation time of liquid xenon, as well as
its scalability, makes it an excellent candidate for PET scanners with
Time-of-Flight measurements, especially for total-body machines. A first
prototype of PETALO is fully operating, devoted to demonstrate the potential of
the concept, measuring the energy and time resolution and to test technical
solutions for a complete ring. The prototype consists of an aluminum box filled
with liquid xenon, with two arrays of SiPMs on opposite sides facing the xenon.
A $\beta$+ emitter source generating 511-keV pairs of gammas is placed in a
central port and the SiPMs record the scintillation light produced by the gamma
interactions, allowing for the reconstruction of the position, the energy and
the time of the interactions.
