Needle artifacts have been a long unsolved challenge in the field of Interventional MRI. The large difference in magnetic susceptibilities between an MR compatible metallic needle or stylet and the surrounding water containing tissue induces significant field perturbations in the vicinity of the needle, which results in signal loss due intra-voxel dephasing, image distortions and signal pileups due to voxel mismapping. These artifacts limit to various extents almost every interventional MRI procedure by obscuring and distorting targets and preventing accurate imaging of the region of interest. This results in reduced targeting accuracies, increased procedure times, inability to monitor therapy and ultimately, reduction in the efficacy of MRI guided procedures. The goal of this proposal is to therefore introduce a proof-of-concept solution for this problem that is inspired by degaussing coil technology used in ships and submarines for defense against magnetic field sensitive sea mines. We propose to develop an active degaussing or shim insert for compensation of needle induced ?B0 and demonstrate correction of susceptibility artifacts in ex-vivo tissue experiments at 3 Tesla.
Aim1 a of this work is dedicated to the simulation of needle and stylet induced field deviations at 3 Tesla that will include the influence of needle material, tip shape and orientation.
Aim 1 b will be focused on the simulation of shim fields and modeling of active shim coils that will compensate the field variations estimated in Aim 1a. The goal in Aim 2 will be the actual fabrication and testing of the needle and needle shim inserts, along with the appropriate electronics for operation of the DC shim coils during imaging. In-scanner calibration and phantom tests will follow bench testing for shim insert coils. Mitigation of artifacts induced by Stainless Steel, Titanium, Nitinol and Brass needles and stylets will be demonstrated in gel phantoms at arbitrary orientations. Finally the goal in Aim 3 will be the demonstration of needle artifact compensation in two different ex-vivo MR guided studies, a biopsy targeting study and an MR thermometry precision experiment. The goal in the first will be to show improved qualitative and quantitative imaging of tissue around the needle and in the second will be to show improved precision of temperature measurements by image phase difference based methods. If successful, the proposed work can spur needle and stylet designs that are self compensated for induced fields for use in a wide spectrum of interventional MRI applications at high field.
Artifacts caused by metallic needles used in MRI guided procedures such as tumor biopsies significantly decrease the visibility of therapy targets and diminish the ability of the physician to accurately perform the procedure. In this project, we propose a novel needle design which can self-compensate for these artifacts and significantly improve the visualization and monitoring of the targeted tissue. The accuracy and overall outcomes of MRI guided treatments can be significantly improved with the proposed needle.
