Design optimization and evaluation of a human brain SPECT-MRI insert based on high-resolution detectors and slit-slat collimators

Multi-modality scanners have become increasingly popular in recent years. While PET/CT, SPECT/CT and PET/MRI systems are now commercially available, SPECT/MRI systems are still in a development phase. The aim of this work was to design a SPECT insert for a conventional MRI scanner in order to perform simultaneous SPECT/MRI studies. The SPECT system will consist of a stationary ring of detectors equipped with multi-pinhole or slit-slat collimators. The detector ring will contain multiple small scintillation detectors with Si-based optical readout units. We have investigated a series of design options using analytical calculations of resolution and sensitivity as well as simulations based on various digital phantoms. Our results show that the highest sensitivity is achieved with a multi-pinhole collimator with 2×2 pinholes per detector. However, due to artifacts appearing as a result of cross-talk related to the parallax effect, a better solution could be the 2-slit slit-slat system, with only 5% lower sensitivity. With a target resolution of 10 mm FWHM, the mean sensitivity over a central ROI for this system was 6.30·10^-4.