Positron-Emission-Tomography (PET) scanners play an important role in cancer diagnosis and molecular imaging. Their accuracy overtakes that of the conventional diagnostics systems. They are used, alone or in combination with other imaging systems, such as CT or MRI. The current best detectors for PET are based on LSO crystals that are usually made of 4mm x 4mm x 10mm coupled to PMT, APD, or similar photon-sensitive device. At best, the FWHM that can be achieved at 511keV is around 10%. This limited energy resolution limits the ability to remove scattered events which are a significant noise contribution to the reconstructed image. The typical length (in the radial direction) of the LSO crystals is about 10mm, which implies a significant uncertainty of the impact point in the radial direction and this induces an error in the projection of the Line of Response. This error deteriorates the quality of the reconstructed image. Pixel-PET uses pixel solid-state-detector coupled to front end electronics. With this novel detector one can achieve the followings: 1- millimeter-size voxel, this means no more parallax effect and hence precise LOR; 2-FWHM energy resolution of less than 1% for 511keV photons. This allows us to eliminate most of the scattered events and thus keep the golden events; 3- Have adequate depth of absorption to achieve high detection efficiency (90%) for 511keV photon; 4- The modular detector has trapezoidal parallelepiped shape thus making it seamless compared to the existing PET system; 5- The conceptual design can be modified to construct a Flat panel detector (Gamma Camera); 6-The design is compatible with MRI making it ideal for Brain imaging. Preliminary Geant4 simulation results, using Derenzo Phantom with Pixel-PET detector suggests that one can achieve the same image quality of the current PET devices but using 25 times less dose.