LightSpin Technologies, Inc., proposes to develop an innovative, solid-state microchannel photodetector (SSMCP) for PET and SPECT applications. This is the first room temperature solid-state photodetector capable of outperforming photomultiplier tubes. The SSMCP is single photons sensitive, but also achieves a wide dynamic range and high linearity. The SSMCP provides high gain (105 - 106), low excess noise factor (ENF < 1.1), ultrafast rise times (< 100 psec), ultrafast timing resolution (<50 psec), operates at low voltage (< 100 V), is compact and robust. In Phase I of this SBIR project, component technologies for the SSMCP were successfully designed, fabricated, and built, and tested, confirming our approach. In Phase II, a large area SSMCP will be demonstrated, with an 8 mm x 8 mm photosensitive area, quantum efficiencies above 20% and dark count rates below 1 Mcps. These large area SSMCPs are expected to improve the performance of PET detectors by providing higher sensitivity, higher timing resolution, improved dynamic range, and superior position sensitivity. ? ? ?