title: Feasibility of using linearly polarized rotating birdcage transmitters and close-fitting receive arrays in MRI to reduce SAR in the vicinity of deep brain simulation implants.
abstract: MRI of patients with deep brain stimulation (DBS) implants is strictly limited due to safety concerns, including high levels of local specific absorption rate (SAR) of radiofrequency (RF) fields near the implant and related RF-induced heating. This study demonstrates the feasibility of using a rotating linearly polarized birdcage transmitter and a 32-channel close-fit receive array to significantly reduce local SAR in MRI of DBS patients.
  
  
  
  Electromagnetic simulations and phantom experiments were performed with generic DBS lead geometries and implantation paths. The technique was based on mechanically rotating a linear birdcage transmitter to align its zero electric-field region with the implant while using a close-fit receive array to significantly increase signal to noise ratio of the images.
  
  
  
  It was found that the zero electric-field region of the transmitter is thick enough at 1.5 Tesla to encompass DBS lead trajectories with wire segments that were up to 30 degrees out of plane, as well as leads with looped segments. Moreover, SAR reduction was not sensitive to tissue properties, and insertion of a close-fit 32-channel receive array did not degrade the SAR reduction performance.
  
  
  
  The ensemble of rotating linear birdcage and 32-channel close-fit receive array introduces a promising technology for future improvement of imaging in patients with DBS implants. Magn Reson Med 77:1701-1712, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Laleh
authors.initials: L
authors.lastname: Golestanirad
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.|Institute of Medical Physics and Radiation Protection, THM, Life Science Engineering, Giessen, Germany.
authors.forename: Boris
authors.initials: B
authors.lastname: Keil
authors.affiliation: Division of Biomedical Physics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, Maryland, USA.
authors.forename: Leonardo M
authors.initials: LM
authors.lastname: Angelone
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Bonmassar
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, USA.
authors.forename: Azma
authors.initials: A
authors.lastname: Mareyam
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts, USA.|Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Wald
mesh_terms: D017076:Computer-Aided Design; D046690:Deep Brain Stimulation / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods; D008280:Magnetics / Q000295:instrumentation*; D019736:Prostheses and Implants; D000069079:Radiation Exposure / Q000032:analysis / Q000517:prevention & control*; D011835:Radiation Protection / Q000295:instrumentation; D012399:Rotation; D014159:Transducers
keywords: MRI; computational modeling; deep brain stimulation (DBS); electrode artifact; finite element modeling; medical implants; safety; specific absorption rate