Simultaneous Emission-Transmission Tomography in an MRI Hardware Framework.

Multi-modality imaging is essential for diagnosis and therapy in challenging cases. A Holy Grail of medical imaging is a hybrid imaging system combining computed tomography (CT), nuclear imaging, and magnetic resonance imaging (MRI) to deliver registered morphological, functional, and cellular/molecular information simultaneously and quantitatively for precision medicine. Recently, a unique imaging approach was demonstrated that combines nuclear imaging with polarized radiotracers and MRI-based spatial encoding. The detection scheme exploits the directional preference of γ-rays emitted from the polarized nuclei, and the result is a concentration image with resolution that can outperform standard nuclear imaging at a sensitivity significantly higher than that of MRI. However, the method does not calculate the attenuation image. Here we propose to obtain MRI-modulated γ-ray data for simultaneous image reconstruction of emission and transmission parameters, which could serve as a stepping stone toward simultaneous CT-SPECT-MRI. This method acquires synchronized datasets to provide insight into morphological features and molecular activities with accurate spatiotemporal registration. We present a complete overview of the system design and the formulation for tomographic reconstruction when the distribution of polarized radiotracers is either global or limited to a region of interest (ROI). Numerical results support the feasibility of our approach and suggest further research topics.