Debora Salvado

In the context of the development of a simultaneous SPECT/MRI system, we have previously proposed a multi-mini-slit-slat (MSS) collimator, with multiple sections of short slits in order to improve the angular sampling. The data can be reconstructed using a 3D reconstruction algorithm that models the collimator geometry. One drawback, however, is that the projection data obtained with this collimator are difficult to interpret visually. Also, calibration can be problematic, as each mini-slit only covers part of the object FoV. We have therefore developed an algorithm for transforming the MSS projection data into the traditional sinogram format. These sinograms consist of multiple thin tilted lines with gaps in between due to the lack of detector rotation in this system. The data can be reconstructed using standard parallel-beam algorithms, taking into account the fact that there are data missing. We have shown with simulations and measurements that the algorithm can transform complex...

A clinical SPECT insert for a commercial MRI scanner has been developed within the INSERT project, allowing simultaneous SPECT/MRI studies of the human brain. Here we present preliminary experimental results. The reconstructed resolution was 6-11 mm and the sensitivity 280-440 s-1/MBq. The INSERT is the first clinical SPECT prototype for simultaneous SPECT/MRI.

ABSTRACT This project’s goal is to design a SPECT insert for a clinical MRI system for simultaneous brain SPECT/MR imaging, with a high-sensitivity collimator and high-resolution detectors. We have compared eight collimator designs, four multi-pinhole and four multi-slit slit-slat configurations. The collimation was designed for a system with 2 rings of 25 detectors. We introduce the concept of 1/2-pinhole and 1/2-slit, which are transaxially shared between two adjacent detectors. Analytical geometric efficiency was calculated for an activity distribution corresponding to a human brain and a range of intrinsic detector resolutions and target resolutions at the centre of the FOV. Noise-free data were simulated with and without depth-of-interaction (DOI) information, 0.8 mm and 10 mm FWHM, and reconstructed for uniform, Defrise, Derenzo, and Zubal brain phantoms. Comparing the multi-pinhole and multi-slit slit-slat collimators, the former gives better reconstructed uniformity and transaxial resolution, while the latter gives better axial resolution. Although the -pinhole and 2-slit designs give the highest sensitivities, they result in a sub-optimal utilisation of the detector FOV. The best options are therefore the -pinhole and the -slit systems, with sensitivities of and , respectively. Noiseless brain phantom reconstructions with the multi-pinhole collimator are slightly superior as compared to slit-slat, in terms of symmetry and accuracy of the activity distribution, but the same is not true when noise is included. DOI information reduces artefacts and improves uniformity in geometric phantoms. Further evaluation is needed with prototype collimators.