While T2K was the first physics experiment to use Multi-Pixel Photon Counters (MPPC) in large quantity, the next major application using large number of MPPCs is expected to be detector for Positron Emission Tomography (PET). Relying on the experience acquired in operating and characterizing MPPCs in T2K, we will show why they are well suited for PET applications. We will show a specific detector concept being developed at TRIUMF, using wavelength shifters to channel the light from the scintillating crystal to the MPPCs. In order to push the PET detector performances beyond the intrinsic limitations of the currently available scintillating crystals, one can further borrow from particle physics by realizing that liquid Xenon is an ideal medium for detecting 511 keV photons. In the second part of the talk, we will present the liquid Xenon TPC concept for PET being developed at TRIUMF.