Applications of radial sampling in interventional MRI

Interventional Magnetic Resonance Imaging (IMRI) is a rapidly emerging application for MRI in which diagnostic and therapeutic procedures are performed under MR image guidance. The success of minimally invasive procedures under MR image guidance depends on various factors like, whether real-time or near-real-time image acquisition is used, the sequence's relative insensitivity to motion and the acquisition's ability to provide accurate and real time guidance and positioning of the interventional device. Current state of art techniques used to satisfy these requirements have limitations that need to be overcome in order to utilize the vast potential of IMRI in minimally invasive procedures.;Radial K-space acquisitions, or more commonly known as projection reconstruction (PR) methods, give rise to various unique and advantageous properties, when compared to rectilinear k-space sampling, by virtue of the way the data is sampled. Research in this project aims at addressing three primary issues that are required for successful IMRI procedures. These are speed/contrast, insensitivity to motion and device tracking. In IMRI patient risk is related to time, and so we developed new rapid steady state radial fluoroscopic acquisitions that also provides comparable contrast and spatial resolution as achieved by current schemes used in IMRI. Results have been presented which indicate that the properties of radial K-space acquisitions can indeed be taken advantage of, in addressing the multiple requirements of MR guided interventional procedures. New motion correction methods are also developed and evaluated, which can be easily integrated into any radial acquisition schemes. These motion correction methods can make the radial acquisition schemes less sensitive to motion and various phase artifacts. The research in this project has also led to design and evaluation of a new method to passively track the device which will overcome the limitations of the current passive methods while incorporating the basic advantages of passive tracking. The feasibility of such a method in interventional arena has been discussed in the appendix. With the ever-improving technologies, present high field systems do present viable alternative for different interventional procedures with the advantages of higher SNR and lower acquisition time. Therefore, feasibility studies for the application of radial acquisition and reconstruction at high fields in cardiac cine imaging have also been performed. Experiments include simulation, in-vitro, ex-vivo, in-vivo trials and assessment of the images using parameters like SNR and CNR. These experiments lead us to making a definitive statement regarding the usefulness of the radial sampling in interventional MRI. The success of this project will lead to the advancement of the field of IMRI beyond the current state of the art.