Project Summary/Abstract Positron emission tomography (PET) is a uniquely powerful medical molecular imaging modality for biological function imaging (e.g. blood flow, energy consumption or binding to cancer cell receptors). It utilizes radioactive molecular tracers that follow physiological processes in the body. A key component of a PET scanner is the block detector that provides location and timing information for every gamma ray detected within a certain energy band. Currently available commercial PET machines achieve a location accuracy of 3 ? 5 mm (in X and Y) and 300 ? 500 psec in time. LightSpin Technologies and the Brain Emission Tomography consortium proposed to develop a new block detector with a location accuracy of 1 mm (in X, Y, and Z) and 50 psec in time. In this SBIR project, LightSpin is proposing to develop a key component of the block detector, namely an innovative silicon photomultiplier (SiPM) array that will not only enable the system to achieve a 50 psec FWHM coincidence timing resolution, but will also integrate 100s of SiPMs on a single chip with integrated, low-power readout electronics providing a multiplexed digital output stream. The approach leverages the best features of custom analog SiPMs (low power, low noise, high quantum efficiency) with the best features of digital SiPMs (high timing efficiency, multiplexed digital output stream) to achieve a substantial improvement in performance, with an ultimate goal of achieving a single photon timing resolution below 50 ps FWHM while maintaining high QE and low power dissipation. The development of these new detector blocks is expected to enable new PET applications such as lightweight, portable brain PET scanners with higher imaging resolution at lower radiation dose for a wide range of applications.