Device visualization for interventional MRI using local magnetic fields: Basic theory and its application to catheter visualization

This paper addresses one of the major problems in Interventional magnetic r esonance imaging (MRI): the visualization of interventional devices. For vi sualization locally induced magnetic fields are used, which disturb the hom ogeneity of the main magnetic field of the MR scanner. This results in sign al loss in the vicinity of the device due to intravoxel dephasing, and lead s to a disturbance of the phase image. The local fields are established by a low current in a closed copper loop along the device. This method will be introduced as a means for catheter visualization. The basic theory behind this method is presented. Simulations are performed to determine the effect of intravoxel dephasing, without interfering effects like susceptibility o r radio-frequency artifacts, Scanned and simulated data is used to verify t he theoretical consideration. Different configurations of mire loops are di scussed and two types of catheter visualization scans are proposed. Results from a pig study show that this methods holds promise for intravascular in terventions under MRI guidance.