Visualization of Conductors Inside an MRI Coil

Abstract

This article reports on the use of fluorocarbons as an imaging medium in MRI. The function of this medium is to uniformly fill the space intended for MR scanning and to provide a strong signal against which objects of interest can be visualized. In our case, such objects were coils used as signal sensors in MRI studies. The aim of the study is visualization of the conductors located inside of an MRI coil and, therefore, could not be visually assessed. To enable the conductor’s imaging, signal amplification from the imaging medium in the vicinity of the conductors was used. The physical phenomenon behind this effect is the fact that the magnetic field induced in the conductor by precessing spins, causing a current in it, which is recorded by the receiver, greatly increases with decreasing distance of the spins from the conductor. The fluorocarbons—octafluorocyclobutane gas—C₄F₈, as well as so-called dry water—perfluoro(2-methyl-3-pentanone)—CF₃CF₂C(O)CF(CF₃)₂ can be used as a visualization medium. In both cases, MRI scan is performed to detect fluorine nuclei (¹⁹F). The method is most effective in active mode—when the coil to be examined is connected to the receiver. The application of the conductor visualization method was shown for three types of two-channel quadrature coils. The ability to visualize the conductors separately for each channel, including volumetric reconstructions, and to construct coil sensitivity maps was demonstrated. ¹⁹F MR images of the coils were compared with their photographs, X-ray and proton MR images, and showed high correspondence.