title: Numerical investigations of MRI RF field induced heating for external fixation devices.
abstract: BACKGROUND
  The magnetic resonance imaging (MRI) radio frequency (RF) field induced heating on external fixation devices can be very high in the vicinity of device screws. Such induced RF heating is related to device constructs, device placements, as well as the device insertion depth into human subjects. In this study, computational modeling is performed to determine factors associated with such induced heating.
  
  
  METHODS
  Numerical modeling, based on the finite-difference time-domain (FDTD) method, is used to evaluate the temperature rises near external device screw tips inside the ASTM phantom for both 1.5-T and 3-T MRI systems. The modeling approach consists of 1) the development of RF coils for 1.5-T and 3-T, 2) the electromagnetic simulations of energy deposition near the screw tips of external fixation devices, and 3) the thermal simulations of temperature rises near the tips of these devices.
  
  
  RESULTS
  It is found that changing insertion depth and screw spacing could largely affect the heating of these devices. In 1.5-T MRI system, smaller insertion depth and larger pin spacing will lead to higher temperature rise. However, for 3-T MRI system, the relation is not very clear when insertion depth is larger than 5 cm or when pin spacing became larger than 20 cm. The effect of connection bar material on device heating is also studied and the heating mechanism of the device is analysed.
  
  
  CONCLUSIONS
  Numerical simulation is used to study RF heating for external fixation devices in both 1.5-T and 3-T MRI coils. Typically, shallower insertion depth and larger pin spacing with conductive bar lead to higher RF heating. The heating mechanism is explained using induced current along the device and power decay inside ASTM phantom.
authors: University of Houston, Houston, TX 77204, USA.
authors: Yan
authors: Y
authors: Liu
authors: Jianxiang
authors: J
authors: Shen
authors: Wolfgang
authors: W
authors: Kainz
authors: Songsong
authors: S
authors: Qian
authors: Wen
authors: W
authors: Wu
authors: Ji
authors: J
authors: Chen
mesh_terms: D003198:Computer Simulation; D004574:Electromagnetic Fields; D016267:External Fixators; D006358:Hot Temperature; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D019047:Phantoms, Imaging; D057233:Radio Frequency Identification Device / Q000379:methods*; D011846:Radio Waves
references: Biomed Eng Online. 2008 Mar 03;7:11
references: 18315869
references: Biomed Eng Online. 2002 Sep 12;1:2
references: 12437766
references: J Magn Reson Imaging. 2013 Feb;37(2):491-7
references: 22851423
references: J Biomed Mater Res B Appl Biomater. 2007 Jul;82(1):17-22
references: 17034016
references: J Magn Reson Imaging. 2013 Aug;38(2):411-6
references: 23293032
references: Nihon Hoshasen Gijutsu Gakkai Zasshi. 2010 Jul 20;66(7):725-33
references: 20702992
references: J Magn Reson Imaging. 2007 Nov;26(5):1328-33
references: 17969167
references: J Magn Reson Imaging. 2007 Nov;26(5):1186-9
references: 17969160
references: J Orthop Res. 2006 Sep;24(9):1799-802
references: 16838376
references: IEEE Trans Biomed Eng. 1998 May;45(5):650-9
references: 9581064