Development of simulation tools for small animal SPECT/MRI reconstruction study

The goal of this study is to develop simulation tools for a proposed simultaneous SPECT/MRI system. The proposed SPECT/MRI system is based on a clinical 3T MRI scanner and a ring-type SPECT subsystem using cadmium zinc telluride (CZT) detectors and pinhole or multi-pinhole collimators. Geant4 applications for emission tomography (GATE) was used to simulate the gamma-ray photon transportation process in SPECT Monte-Carlo simulation. Analytical modeling of the electron-hole drifting was used to simulate CZT detector response in the magnetic field. Object-oriented development interface for NMR (ODIN) was introduced to simulate MR imaging sequences. The digital mouse whole body (MOBY) phantom was extended for MRI simulation by specifying the spin-physics properties for each organ in the mouse phantom. The data generated from the above simulation tools was then employed to study how to improve SPECT reconstruction using anatomical information based on MRI images. The noise and lesion contrast properties of reconstructed SPECT images were discussed. We conclude that the simulation tools are useful for investigating how to improve SPECT reconstruction using MRI images in the simultaneous SPECT/MRI imaging systems under construction or investigation.