Reconstruction of multi-pinhole SPECT data with correction of attenuation, scatter and intrinsic detector resolution

Abstract

Multi-pinhole SPECT collimators can provide sub-millimeter resolution and improved sensitivity over single-pinhole and parallel-beam collimators. Attenuation and scatter will degrade the quantitative accuracy of reconstruction for lower energy emitters like I-125 and therefore both effects should be accounted for during reconstruction. We implemented an OSEM MAP reconstruction which incorporated attenuation, scatter and detector intrinsic resolution for a multi-pinhole detector designed for whole-body mouse imaging. The ray- driven projector/backprojector implemented considerably reduced the calculation of attenuation factors and decreased reconstruction time compared to a voxel-driven approach. The multi-pinhole SPECT system simulated consists of 2 or 4 cameras, with a 5-pinhole collimator plate for each. The attenuation map would be obtained from a CT system mounted on the same gantry. Scatter is estimated from scatter windows using a triple energy window (TEW) method and applied during the iterative reconstruction. A quadratic smoothness prior is implemented to control noise. Simulations with the MOBY mouse phantom show that modeling of the pinhole sensitivity, attenuation and detector intrinsic resolution results in a more accurate reconstruction. Preliminary Monte Carlo simulations showed the importance of determining and correcting the attenuation and scatter for I-125 imaging. Further investigations will be performed towards accurate estimation of the point-spread-function or sensitivity model of the multi-pinhole collimator plate.