Accurate Localization of Metal Electrodes Using Magnetic Resonance Imaging

Abstract

Purpose : Localization using MRI is difficult due to susceptibility induced artifacts caused by metal electrodes. Here we took an advantage of the B0 pattern induced by the metal electrodes by using an oblique-view imaging method. Materials and Methods : Metal electrode models with various diameters and susceptibilities were simulated to understand the aspect of field distortion. We set localization criteria for a turbo spin-echo (TSE) sequence usingconventional (90� view) and 45�oblique-view imaging method through simulation of images with various resolutions and validated the criteria usingphantom images acquired by a 3.0T clinical MRI system. For a gradient-refocused echo (GRE) sequence, which is relatively more sensitive to field inhomogeneity, we used phase images to find the center of electrode. Results : There was least field inhomogeneity along the 45�line that penetrated the center of the electrode. Therefore, our criteria for the TSE sequence with 45� obliqueview was coincided regardless of susceptibility. And with 45�oblique-view angle images, pixel shifts were bidirectional so we can detect the location of electrodes even in low resolution. For the GRE sequence, the 45�oblique-view anglemethod madethe lines where field polarity changes become coincident to the Cartesian grid so the localization of the center coordinates was more facilitated. Conclusion : We suggested the method for accurate localization of electrode using 45� oblique-view angle imaging. It is expected to be a novelmethodto monitoring an electrophysiological brain study and brain neurosurgery.

Efficient Experimental Design for Measuring Magnetic Susceptibility of Arbitrarily Shaped Materials by MRI

“…In case of the gray cuboid from Makerbot 3D printer and the aluminum and copper alloys, there were artifacts around the material in the third images when water was used as the filling liquid. This is suspected to be partly due to relatively large difference of the magnetic susceptibility between the object and background water (9,10). To reduce the mismatch, Gd-DOTA solution with estimated susceptibility of 8.5 ppm was used instead of water in the third imaging for the grey cuboid.…”