Optimization of a stationary small animal SPECT system for simultaneous SPECT/MRI

In a preclinical molecular imaging, hybrid SPECT and MRI equipment can provide improved spatial resolution as compared to PET/MRI. Current efforts in preclinical SPECT/MRI are limited to experimental systems designed for integration in large bore MRI systems. Consequently, compromises are made in image quality, either for SPECT or for MRI. Therefore, a SPECT/MRI system should be developed that provides state-of-the-art performance for both the SPECT and the MRI part. The main challenges are the small space constraints, magnetic and RF compatibility and full stationarity. We are currently investigating the use of DPC digital silicon photomultipliers for use as a SPECT detector with the final goal of providing a stationary SPECT insert for a preclinical MRI scanner with 10cm inside diameter. A system optimization procedure is described and results in an octagonal system consisting of 2 axial rings. An average sensitivity of 0.26% can be obtained in combination with a theoretical system resolution of 1.4 mm. Simulations of this optimal system show a reconstructed resolution of 800 μm and shows that reconstruction of the heart of a mouse in a realistic imaging situation is possibte. The application of these findings will lead to a SPECT system that can be used ror simultaneous SPECT/MRI without compromising SPECT image quality.