Small Animal PET Camera Design Based on 2-mm Straw Detectors

Depth of interaction (DOI) errors in commonly employed crystal detectors cause severe degradation of off-axis resolution in current positron emission tomography (PET) scanners used for small animal or single organ imaging. We propose a PET camera design that uses low cost, easily fabricated, lead-walled straw (LWS) detectors. Photons converted in Pb generate photoelectrons that escape into the straw interior producing an avalanche whose position can be readily measured with high precision. Straws can be of considerable length (up to 50 cm), but small in diameter (2 mm), and can be packed to form scanners with high sensitivity and large fields of view (FOV). The rigorous three-dimensional position encoding eliminates DOI errors encountered in crystal detectors, and provides submillimeter resolution and sensitivity response that is uniform over the full extent of the FOV. We present preliminary results of the operation of a prototype 200-straw module. We then propose a PET scanner design that consists of two rotating trapezoidal detector panels, each panel containing fourteen 200-straw modules (a total of 5600 straws). The FOV has a diameter of 5 cm and extends axially to 15 cm. This unique geometry affords a long field of view, with near constant axial sensitivity of 4.7%, and uniform resolution of 0.9 times 0.9 times 1.0 mm3 maintained over the entire extent of the FOV, as determined in Monte Carlo simulations.