Feasibility studies of animal SPECT imaging with a stationary multi-pinhole collimator inserted to animal PET detector ring

In this study, we design a stationary multi-pinhole SPECT collimator inserted to a small animal PET scanner and investigate the feasibility of SPECT imaging in this system with Monte Carlo simulation studies. Compared to preceding approaches, the unique aspect of the proposed design is that it enables SPECT imaging only by axial translation of the imaging object to obtain sufficient angular sampling, rather than rotation of either the object or the collimator. This reduces the difficulty of geometrical calibration and facilitates accurate system matrix derivation. In order to minimize the axial overlap, the transverse section of the pinhole is designed to be elliptical. The sampling completeness of different scanning orbits is studied by a numerical approach based on Tuy sampling criteria. Results show that in the reconstruction images of a simulated Derenzo phantom, 1.35 mm hot rods are distinguishable. Image quality with only object translation is comparable to those with both object translation and rotation. A practical calibration method of the system geometrical parameters is developed and tested with simulation data. Finally, we incorporate the TV prior in OS-EM algorithm and the reconstruction results show the noise is efficiently suppressed. We conclude that we present a practical way to implement SPECT imaging on existing PET scanner without object or collimator rotation and desired spatial resolution is achievable with this design.