IADR Abstract Archives
Design and Optimization of an Intraoral MRI Coil for Dental Imaging
Objectives: There are no commercially available intraoral radiofrequency (RF) coils for dental MRI applications. An intra-oral coil has the advantage of higher signal-to-noise ratio (SNR) than the coils placed outside the body. This research sought to optimize intraoral RF coil design.
Methods: Targeted design features for optimization were: eliminate distal proportion of the loop coil restraining tongue movement, production of a uniform sensitivity throughout the coil, increased penetration depth for capturing signal from roots, and elimination of coupling between coil elements. Initial design was simulated using an electromagnetic simulation tool based on finite-difference-time-domain (FDTD) approach (Sim4Life v5.0, ZMT, Zurich, Switzerland). Testing prototypes was conducted on 4T MRI system using SWeep-Imaging-with-Fourier-Transform (SWIFT) pulse sequence on extracted teeth and human volunteers.
Results: Multiwire curved dipole antenna in form of a double-sided dental impression tray was designed and constructed using 7 of 1.2mm diameter enameled copper wires for each dipole arm, inserted in acrylonitrile-butadiene-styrene (ABS) wire tracks and electrically isolated. Uniform sensitivity profile was obtained by addition of BaTiO3 slurry at the tip of the dipole arms with the length optimized using FDTD simulations. For 15 mm-long high-permittivity section, the sensitivity change was reduced from 89% to 50% over 75mm distance along the dipole arm. FDTD simulations demonstrated 24mm penetration depth using 7 wires, whereas increasing number of wires did not result in significant improvement. Concomitant use of intraoral dipole antenna with extraoral transmission line resonators (TLR) increased signal penetration, where coupling between the dipole and TLR elements was less than -35dB. Phantom images of intraoral dipole, and combination of dipole and TLR yielded SNRs of 5.2, and 5.3, respectively within a region-of-interest around a cracked root sample.
Conclusions: We demonstrated feasibility of using a dipole antenna as an intraoral coil and optimized the electromagnetic properties of this coil.
Methods: Targeted design features for optimization were: eliminate distal proportion of the loop coil restraining tongue movement, production of a uniform sensitivity throughout the coil, increased penetration depth for capturing signal from roots, and elimination of coupling between coil elements. Initial design was simulated using an electromagnetic simulation tool based on finite-difference-time-domain (FDTD) approach (Sim4Life v5.0, ZMT, Zurich, Switzerland). Testing prototypes was conducted on 4T MRI system using SWeep-Imaging-with-Fourier-Transform (SWIFT) pulse sequence on extracted teeth and human volunteers.
Results: Multiwire curved dipole antenna in form of a double-sided dental impression tray was designed and constructed using 7 of 1.2mm diameter enameled copper wires for each dipole arm, inserted in acrylonitrile-butadiene-styrene (ABS) wire tracks and electrically isolated. Uniform sensitivity profile was obtained by addition of BaTiO3 slurry at the tip of the dipole arms with the length optimized using FDTD simulations. For 15 mm-long high-permittivity section, the sensitivity change was reduced from 89% to 50% over 75mm distance along the dipole arm. FDTD simulations demonstrated 24mm penetration depth using 7 wires, whereas increasing number of wires did not result in significant improvement. Concomitant use of intraoral dipole antenna with extraoral transmission line resonators (TLR) increased signal penetration, where coupling between the dipole and TLR elements was less than -35dB. Phantom images of intraoral dipole, and combination of dipole and TLR yielded SNRs of 5.2, and 5.3, respectively within a region-of-interest around a cracked root sample.
Conclusions: We demonstrated feasibility of using a dipole antenna as an intraoral coil and optimized the electromagnetic properties of this coil.