  Liquid xenon has several attractive features, which make it suitable for
applications to nuclear medicine, such as high scintillation yield and fast
scintillation decay time, better than currently used crystals. Since the '90s,
several attempts has been made to build Positron Emission Tomography scanners
based on liquid xenon, which can be divided into two different approaches: on
one hand, the detection of the ionization charge in TPCs, and, on the other
one, the detection of scintillation light with photomultipliers.
  PETALO (Positron Emission Tof Apparatus with Liquid xenOn) is a novel
concept, which combines liquid xenon scintillating cells and silicon
photomultipliers for the readout. A first Monte Carlo investigation has pointed
out that this technology would provide an excellent intrinsic time resolution,
which makes it possible to measure the Time-Of-Flight with high efficiency.
Also, the transparency of liquid xenon to UV and blue wavelengths opens the
possibility of exploiting both scintillation and Cherenkov light for a
high-sensitivity TOF-PET.
