Preliminary evaluation of the tomographic performance of the MediSPECT small animal imaging system

We report on the tests of a prototype (MediSPECT) system developed at University & INFN Napoli, for Single Photon Emission Computed Tomography (SPECT) imaging on small animals with a small Field of View (FoV) and high spatial resolution. MediSPECT is a SPECT imaging system based on a 1-mm-thick CdTe pixel detector, bump-bonded to the Medipix2 CMOS readout circuit operating in single-photon counting. The CdTe detector has 256X256 square array of pixels arranged with a 55 micron pitch, for a sensitive area of 14X14mm^2. In its present version, this system implements a single detector head, mounted on a rotating gantry. For preliminary testing and calibration of the acquisition equipment and image reconstruction algorithms, 90 projections of a gamma-ray point source (109-Cd) through a single pinhole (diameter 0.4 mm; radius of rotation about 2.5 cm; focal length about 4.5 cm) were acquired for 20 min each in a stepand- shoot mode. Capillaries, 800 mm in diameter, were arranged in a Y-shape to form a more complex phantom (125-I, 1mm pinhole diameter, 45 projections, each acquired for 25 min). Images were reconstructed with a custom algorithm implementing standard OS-EM with center of rotation correction and spatial resolution of 0.2mm over a FoV of 2mm was obtained.