  With the newly gained interest in the time of flight method for positron
emission tomography (TOF-PET), many options for pushing the time resolution to
its borders have been investigated. As one of these options the exploitation of
the Cherenkov effect has been proposed, since it allows to bypass the
scintillation process and therefore provides almost instantaneous response to
incident 511keV annihilation photons. Our simulation studies on the yield of
Cherenkov photons, their arrival rate at the photon detector and their angular
distribution reveal a significant influence by Cherenkov photons on the rise
time of inorganic scintillators - a key-parameter for TOF in PET. A measurement
shows the feasibility to detect Cherenkov photons in this low energy range.
