title: Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation.
abstract: OBJECTIVE
  MRI-guided real-time transcranial magnetic stimulation (TMS) navigators that apply electromagnetic modeling have improved the utility of TMS. However, their accuracy and speed depends on the assumed volume conductor geometry. Spherical models found in present navigators are computationally fast but may be inaccurate in some areas. Realistically shaped boundary-element models (BEMs) could increase accuracy at a moderate computational cost, but it is unknown which model features have the largest influence on accuracy. Thus, we compared different types of spherical models and BEMs.
  
  
  METHODS
  Globally and locally fitted spherical models and different BEMs with either one or three compartments and with different skull-to-brain conductivity ratios (1/1-1/80) were compared against a reference BEM.
  
  
  RESULTS
  The one-compartment BEM at inner skull surface was almost as accurate as the reference BEM. Skull/brain conductivity ratio in the range 1/10-1/80 had only a minor influence. BEMs were superior to spherical models especially in frontal and temporal areas (up to 20mm localization and 40% intensity improvement); in motor cortex all models provided similar results.
  
  
  CONCLUSIONS
  One-compartment BEMs offer a good balance between accuracy and computational cost.
  
  
  CONCLUSIONS
  Realistically shaped BEMs may increase TMS navigation accuracy in several brain areas, such as in prefrontal regions often targeted in clinical applications.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02129, USA. nummenma@nmr.mgh.harvard.edu
authors.forename: Aapo
authors.initials: A
authors.lastname: Nummenmaa
authors.forename: Matti
authors.initials: M
authors.lastname: Stenroos
authors.forename: Risto J
authors.initials: RJ
authors.lastname: Ilmoniemi
authors.forename: Yoshio C
authors.initials: YC
authors.lastname: Okada
authors.forename: Matti S
authors.initials: MS
authors.lastname: Hämäläinen
authors.forename: Tommi
authors.initials: T
authors.lastname: Raij
mesh_terms: D001921:Brain / Q000033:anatomy & histology / Q000502:physiology; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography / Q000379:methods; D004574:Electromagnetic Fields; D006257:Head / Q000033:anatomy & histology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008953:Models, Anatomic; D008959:Models, Neurological; D009431:Neural Conduction; D009929:Organ Size; D017397:Prefrontal Cortex; D013702:Temporal Lobe; D050781:Transcranial Magnetic Stimulation / Q000295:instrumentation*
keywords: Boundary element method; Electromagnetic modeling; Image guided navigation; Transcranial magnetic stimulation
references.citation: IEEE Trans Biomed Eng. 2003 Sep;50(9):1074-85
references.pmid: 12943275
references.citation: Biophys J. 1967 Jan;7(1):1-11
references.pmid: 19210978
references.citation: Biophys J. 1973 Sep;13(9):911-25
references.pmid: 4733699
references.citation: Hum Brain Mapp. 2013 Apr;34(4):923-35
references.pmid: 22109746
references.citation: Curr Opin Neurobiol. 2000 Apr;10(2):232-7
references.pmid: 10753803
references.citation: IEEE Trans Biomed Eng. 1997 Aug;44(8):727-35
references.pmid: 9254986
references.citation: Phys Med Biol. 2012 Jun 7;57(11):3517-35
references.pmid: 22581305
references.citation: Neuroimage. 2007 Jul 15;36(4):1159-70
references.pmid: 17524673
references.citation: Neurophysiol Clin. 2010 Mar;40(1):7-17
references.pmid: 20230931
references.citation: Int J Neuropsychopharmacol. 2000 Sep;3(3):259-273
references.pmid: 11343603
references.citation: IEEE Trans Biomed Eng. 1999 Mar;46(3):245-59
references.pmid: 10097460
references.citation: Neuroimage. 2011 Oct 1;58(3):849-59
references.pmid: 21749927
references.citation: Proc Natl Acad Sci U S A. 2001 Sep 25;98(20):11697-701
references.pmid: 11573005
references.citation: Hum Brain Mapp. 2005 Oct;26(2):100-9
references.pmid: 15864816
references.citation: Phys Med. 2008 Jun;24(2):80-6
references.pmid: 18296093
references.citation: Neuroimage. 2004;23 Suppl 1:S69-84
references.pmid: 15501102
references.citation: J Neurosci Methods. 2009 Apr 30;179(1):111-20
references.pmid: 19428517
references.citation: Neuroimage. 2011 Jan 1;54(1):234-43
references.pmid: 20682353
references.citation: J Clin Neurophysiol. 1991 Jan;8(1):112-20
references.pmid: 2019646
references.citation: Electroencephalogr Clin Neurophysiol. 1983 Jul;56(1):38-51
references.pmid: 6190632
references.citation: Muscle Nerve. 1990 Aug;13(8):734-41
references.pmid: 2385260
references.citation: Phys Med Biol. 2005 Oct 7;50(19):4695-710
references.pmid: 16177498
references.citation: Comput Methods Programs Biomed. 2007 Dec;88(3):256-63
references.pmid: 18022274
references.citation: J Clin Neurophysiol. 1991 Jan;8(1):102-11
references.pmid: 2019645
references.citation: Neurosurgery. 2011 Nov;69(5):1015-29; discussion 1029
references.pmid: 21709597
references.citation: Med Biol Eng Comput. 2012 Jul;50(7):671-81
references.pmid: 22678596
references.citation: Neuroimage. 1999 Feb;9(2):179-94
references.pmid: 9931268
references.citation: IEEE Trans Biomed Eng. 1992 Jan;39(1):58-64
references.pmid: 1572682
references.citation: Electroencephalogr Clin Neurophysiol. 1991 Jun;81(3):238-9
references.pmid: 1710973
references.citation: Neuroimage. 2006 Jul 1;31(3):968-80
references.pmid: 16530430
references.citation: Phys Med Biol. 1990 Aug;35(8):1119-28
references.pmid: 2217537
references.citation: Cereb Cortex. 2004 Jan;14(1):11-22
references.pmid: 14654453
references.citation: Phys Med Biol. 2009 Aug 21;54(16):4863-78
references.pmid: 19636081
references.citation: Phys Med Biol. 2009 Jun 21;54(12):3631-47
references.pmid: 19458407
references.citation: Crit Rev Biomed Eng. 1999;27(3-5):241-84
references.pmid: 10864281
references.citation: Biophys J. 1992 Jul;63(1):129-38
references.pmid: 1420862
references.citation: Biol Psychiatry. 2009 Sep 1;66(5):509-15
references.pmid: 19545855
references.citation: IEEE Trans Biomed Eng. 1997 Nov;44(11):1139-55
references.pmid: 9353994
references.citation: Anesth Analg. 1968 Nov-Dec;47(6):717-23
references.pmid: 4972743
references.citation: IEEE Trans Biomed Eng. 2004 Sep;51(9):1586-98
references.pmid: 15376507
references.citation: Appl Phys Lett. 2006;89(22):223903-2239033
references.pmid: 17492058
references.citation: IEEE Trans Biomed Eng. 2000 Nov;47(11):1487-92
references.pmid: 11077742
references.citation: IEEE Trans Biomed Eng. 1972 May;19(3):239-44
references.pmid: 5021223
references.citation: Phys Med Biol. 1987 Jan;32(1):11-22
references.pmid: 3823129
references.citation: J Clin Neurophysiol. 2007 Apr;24(2):101-19
references.pmid: 17414966
references.citation: Clin Neurophysiol. 2003 Oct;114(10):1977-92
references.pmid: 14499760
references.citation: Neuroimage. 1999 Feb;9(2):195-207
references.pmid: 9931269
references.citation: Neuroimage. 2012 Aug 15;62(2):774-81
references.pmid: 22248573
references.citation: Lancet. 1985 May 11;1(8437):1106-7
references.pmid: 2860322
references.citation: IEEE Trans Biomed Eng. 1989 Feb;36(2):165-71
references.pmid: 2917762
references.citation: Hum Brain Mapp. 2004 May;22(1):1-14
references.pmid: 15083522
references.citation: J Cogn Neurosci. 2009 Feb;21(2):207-21
references.pmid: 18823235