A high efficiency small animal imaging system based on position sensitive avalanche photodiodes

Abstract

Single photon emission computed tomography (SPECT) is an important technology for molecular imaging studies of small animals with an increasing demand for high performance imaging systems. We have designed a small animal imaging system based on position sensitive avalanche photodiodes (PSAPDs) detectors with the goal of submillimeter spatial resolution and high detection efficiency, which will allow us to minimize the radiation dose to the animal and to shorten the time needed for the imaging study. Our design will use fourteen 80×80 mm² PSAPD detectors, which can achieve an intrinsic spatial resolution of 0.5 mm. These detectors are arranged in two rings around the object and are equipped with pinhole collimators to produce magnified projection data. A mouse bed is positioned in the center of the detector rings and can be rocked about the central axis to increase angular sampling of the object. The performance of this imaging system and of a dual headed SPECT system has been simulated using a ray tracing program taking into account appropriate point spread functions. Projection data of a hot rod phantom with 84 angular samples have been simulated. Appropriate Poisson noise has been added to the data to simulate an acquisition time of 15 min and an activity of 18.5 MBq distributed in the phantom. Both sets of data were reconstructed with an ML-EM reconstruction algorithm. We also derived spatial resolution and detection efficiency from analytical equations and compared the performance of our system to a variety of other small animal SPECT imaging systems. Simulations show that our proposed system produces a spatial resolution of 0.9 mm which is in good agreement with the resolution derived from analytical equations. In contrast, simulations of the dual headed SPECT system produce a spatial resolution of 1.1 mm. In comparison to other small animal SPECT systems, our design will offer a detection efficiency which is at least 2-fold higher at better or comparable spatial resolution. These results suggest that detectors based on PSAPD technology can be used to improve the design of small animal SPECT imaging systems considerably. Our small animal system design is very compact and can achieve high resolution and detection efficiency.