Document Type : Conference Proceedings
Radiation Application Research School, Nuclear Science and Technology Research Institute, Tehran, Iran.
Radiation Medicine Department, Shahid Beheshti University, Tehran, Iran.
Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran. Research Center for Molecular and Cellular Imaging, Tehran University of Medical Sciences, Tehran, Iran.
Introduction: While the necessity of replacing voxels with blobs in conventional tomographic reconstruction based upon line-integrals is clear, it is not however well-investigated in plane- integral-based reconstruction. The problem is more challenging in convergent-plane projection reconstruction. In this work, we are aiming at utilizing blobs as alternative to voxels.
Materials and Methods: To doing so, a spinning slithole collimated small-animal SPECT scanner was modeled within GATE simulator and SPECT data acquisition was performed for NEMA IQ phantom. The slithole provides convergent-plane-integral projections of the object being imaged. The collimation data were then reconstructed using an ad hoc 3D OSEM algorithm based upon plane-integral projections using cubic voxels. The image reconstruction was repeated for blobs. Various figures of merit were assessed in order to compare voxel and blob reconstructions.
Results: Both voxel and blob reconstruction algorithms were verified using a noisy 3D Shepp- Logan phantom prior to reconstructing the simulation data, with an error of 6% and 9%, respectively. Blob modeling leads to a lower computation burden by a factor of ~2.1 in on- the-fly calculation of the system matrix. A 13% increase in SNR of the hottest rod of the NEMA IQ phantom is obtained when voxels are replaced by blobs. Blob reconstruction shows an advantage over voxel reconstruction by offering a monotonically decreasing NSE across all iterations indicating a more robust statistical noise handling.
Conclusion: Voxels are simple and easy-to-implement, but blobs outperforms them by exhibiting a much more efficient projector/backprojector pair due to their inherent symmetric and smooth shape. Therefore, blobs should be the basis functions of choice in the case of plane-integral-based reconstruction.