T. Vargo, K. Grossman, J. Miragliotta, A. Hope
Integument Technologies, Inc.,
Keywords: MRI, electromagnetic interference, metamaterials, frequency selective surfaces
Summary:Integument Technologies, Inc. (ITI) has partnered with the Johns Hopkins University Applied Physics Laboratory (JHU/APL) to create metamaterials to act similar to band-stop filters. These metamaterials can be added to compliment traditional shielding enclosure materials, and customized to mitigate the most detrimental EMI at the Larmor frequency of MRI instrumentation. The resulting system will provide highly effective, lightweight, and easily fieldable electromagnetic isolation to improve the signal-to-noise ratio of fielded systems. Magnetic resonance imaging (MRI) installations incorporate expensive electromagnetic interference (EMI) shielding enclosures, Faraday cages, that protect over a wide frequency range. These cages are susceptible to leaking radiation, especially at higher frequencies where the MRI units are especially vulnerable to interference. Mitigating these leaks can be difficult with traditional materials. A new metamaterial based approach, using a narrow band shield that is centered around the operating frequency of the MRI, could reduce the cost of these enclosures and improve the performance of the MRI units. MRI develops images by measuring the spatially emitted energy of protons relaxing into alignment with the primary magnetic field. These signals occur at the Larmor frequency of the MRI equipment’s applied magnetic field. The goal of metamaterial-based MRI equipment shielding is to improve the efficacy of MRI equipment by absorbing environmental EM noise that represents an interference at or near the Larmor frequency. Reduction of noise improves the quality and resolution of an MRI image, quantified by the signal-to-noise ratio (SNR). Metamaterials have found their way into commercialized products, including, for example, as antennas in cell phones. While some metamaterial structures appear simple, their precise design requires computer aided design and simulation software in order to match their properties with the specific application. EMI shielding of MRI installations represents a new application for metamaterials, requiring developmental work. ITI and APL recently completed a proof-of concept project incorporating metamaterials for EMI shielding of walk-in enclosures across a broad EM band for protection of military communications shelters. However, by their nature metamaterials are best suited for narrow-band applications. As such, we anticipate that EM shielding of MRI installations is a natural extension of metamaterial technology, and the team is actively seeking partners to help demonstrate and develop this application.