A novel photon detector, the Silicon Photo-multiplier (SiPM), has been tested as a photosensitive device for Positron Emission Tomography (PET). PET is one of the most important non-invasive methods for in-depth and in-vivo imaging of tissue. The SiPM has advantages over existing photon detectors as it can be used in a magnetic field, has a better resolution and is easier to operate. The results of measurements of spatial dependence variation in response for individual SiPMs are presented. A PET module has been constructed by coupling an array of Photonique 2.1mm × 2.1mm SiPMs to LYSO scintillation crystals. The properties of the module prototype are presented.