An ideal dielectric coat to avoid prosthesis RF-artefacts in Magnetic Resonance Imaging

Abstract

The number of people submitted to total hip or knee arthroplasty increased in the last years and it is likely to grow further. Hence, the importance of a proper investigation tool that allows to determine and recognize the potential presence of perioperative and/or postoperative diseases becomes clear. Although the Magnetic Resonance Imaging (MRI) technique demonstrated several advantages over the other common tomography tools, it suffers from the arise of image artefacts if it is performed in presence of metallic prostheses. In particular, the so-called RF-artefacts are caused by the inhomogeneity in the radiofrequency magnetic field of MRI, due to the electric currents induced on the metal surface by the field itself. In this work, a near-zero permittivity dielectric coat is simulated to reduce those currents and, therefore, the RF-artefacts onset in the final image. Numerical results confirm that the dielectric coat strongly reduces the magnetic field inhomogeneity, suggesting a possible solution to a well-known problem in the MRI field.

A Near-Field Cloaking Study to Reduce MRI RF-Artefacts in Presence of Elongated Prostheses

“…In order to have a term of comparison for the results proposed below, some general results are reported in Fig. 3 (see also [16]). Fig.…”

“…with an Epsilon Near Zero (ENZ) ideal dielectric coat to hide it to the RF antenna [16]. In particular, they showed heuristically, by means of numerical simulations, that a 1 mm thick dielectric coat made with a zero-conductivity and 0.1 relative permittivity material, strongly decreases the RF-artefacts onset.…”

“…Since the type of coupling depends also on the geometry of the involved components, it will be shown how it is possible to operate only on the prevailing kind of coupling to obtain relatively simple material parameters. footnotetext In [16], the cloaking results were provided considering a specific coat whose properties were obtained through a heuristic procedure. In this work, a particular approach for near-field cloaking is presented by means of a simplified but effective circuital model and numerical simulations.…”

Heating of hip joint implants in MRI: The combined effect of RF and switched‐gradient fields

“…Methods for reducing the heating induced by the interaction between RF fields and metallic implants have been proposed 44‐47 . These include using an elliptical rather than circular polarization of the B 1 field, 45 parallel transmission techniques, 46 or a cloaking strategy 47 .…”

“…Methods for reducing the heating induced by the interaction between RF fields and metallic implants have been proposed. [44][45][46][47] These include using an elliptical rather than circular polarization of the B 1 field, 45 parallel transmission techniques, 46 or a cloaking strategy. 47 Other options to reduce temperature increase due to both RF and GC fields include changing the deployed sequence when possible, tuning the RF pulse parameters (see, for example, the effects in the case of TrueFISP reported in Table 4), and varying the frequency encoding direction (especially for EPI 29 ).…”