Toward real-time dynamic imaging in an X-ray/MR (XMR) hybrid system, including chemical species separation

Both x-ray fluoroscopy and Magnetic Resonance Imaging (MRI) have been used for image-guided interventions. They have complementary strengths and weaknesses, a fact that has led to the emergence of X-ray/MR (XMR) hybrid systems. Such systems provide a platform for developing new image guidance concepts and applying advanced dynamic imaging techniques.; The first part of this dissertation proposes and validates the concept of a real-time XMR interface for the hybrid system. This interface enables interactive and integrated use of images from both modalities. An essential step to implement this interface is co-registration of the x-ray and MR fields-of-view (FOVs). A fiducial-based registration scheme is developed. One potential application of the real-time interface, called XScout, is use of x-ray images as scouts to prescribe MR slices. The registration accuracy and the feasibility of XScout were demonstrated by computer simulations and phantom experiments. Software and communication protocols were built to implement the real-time interface.; Dynamic or real-time imaging is required for image-guided interventional procedures. Fast and flexible acquisitions are essential. Being able to show reliable and clear contrast of chemical species of interest is also desirable. The second part of this dissertation concerns chemical species separation techniques in MRI, mainly water-fat separation. A recent water-fat decomposition method, called IDEAL, has shown greater flexibility and superior noise performance compared with conventional methods. In this dissertation IDEAL is improved and tailored for dynamic imaging applications. In particular, the robustness of the field map estimation in IDEAL reconstruction is improved. An accelerated acquisition scheme, 1+-point water-fat separation, is proposed to remove IDEAL's limitation of tripled scan-time. The 1 +-point method offers reliable and fast water-fat separation for dynamic imaging applications. Furthermore, the combined water-fat images free of chemical shift artifact can be a valuable side benefit for IDEAL acquisitions.; A strategy for MR imaging during percutaneous vertebroplasty (PV) is discussed. In order for PV to potentially benefit from imaging with the XMR system, a multi-species (fat, water, Polymethylmethacrylate[PMMA]) separation method, an extension of IDEAL, is proposed.; The dissertation concludes with a discussion of extensions and future work.