This article describes a new 5-head LSO-panel-detector PET prototype built by CPS Innovations. Transaxial spatial resolution for this prototype is measured and reported. This new tomograph is characterized by extremely high sensitivity (expected to be 2 to 7 times that of other ECAT tomographs,) a long field of view (FOV) axis (52cm), and a wide FOV diameter (70cm) while maintaining excellent spatial resolution (0.5cm or better). This prototype is a continuously rotating (30 RPM) tomograph which supports 3 or 5 planar LSO detector arrays. Each detector array (head) contains 84/spl times/120 LSO crystals arranged as a single panel-2cm deep. This panel is 36cm wide (transaxial) and 52cm long (axial) with each crystal 0.44/spl times/0.44/spl times/2cm. The 5 planar heads are arranged as 5 of 6 sides of a hexagon. Radial distance from FOV center to the crystal face of each of the LSO panels is 43cm. Early measurements for transaxial spatial resolution were made with a 0.16cm diameter (/sup 68/Ge/Ga) needle source held parallel to FOV axis. The 120 crystal "rings" form 239 transaxial (segment 0) planes. Of these 0-to-238 (span 7) planes, planes 10, 120, & 230 were used to collect resolution data. The needle was placed nominally at the following radial distances from FOV center: 0, 1, 10, 20, 30cm. Here respectively are initial resolution results (5 radial positions, each an average for the 3 planes): 0.49, 0.51, 0.57, 0.70, 0.74cm. These initial resolution numbers are expected to improve significantly with nearly complete refinements to data acquisition and nearest-neighbor LOR rebinning.