title: Magnetic susceptibility induced white matter MR signal frequency shifts--experimental comparison between Lorentzian sphere and generalized Lorentzian approaches.
abstract: OBJECTIVE
  The nature of the remarkable phase contrast in high-field gradient echo MRI studies of human brain is a subject of intense debates. The generalized Lorentzian approach (He and Yablonskiy, Proc Natl Acad Sci USA 2009;106:13558-13563) provides an explanation for the anisotropy of phase contrast, the near absence of phase contrast between white matter and cerebrospinal fluid, and changes of phase contrast in multiple sclerosis. In this study, we experimentally validate the generalized Lorentzian approach.
  
  
  METHODS
  The Generalized Lorentzian Approach suggests that the local contribution to frequency shifts in white matter does not depend on the average tissue magnetic susceptibility (as suggested by Lorentzian sphere approximation), but on the distribution and symmetry of magnetic susceptibility inclusions at the cellular level. We use ex vivo rat optic nerve as a model system of highly organized cellular structure containing longitudinally arranged myelin and neurofilaments. The nerve's cylindrical shape allowed accurate measurement of its magnetic susceptibility and local frequency shifts.
  
  
  RESULTS
  We found that the volume magnetic susceptibility difference between nerve and water is -0.116 ppm, and the magnetic susceptibilities of longitudinal components are -0.043 ppm in fresh nerve, and -0.020 ppm in fixed nerve.
  
  
  CONCLUSIONS
  The frequency shift observed in the optic nerve as a representative of white matter is consistent with generalized Lorentzian approach but inconsistent with Lorentzian sphere approximation.
authors: Department of Radiology, Washington University, St. Louis, Missouri, USA.
authors: J
authors: J
authors: Luo
authors: X
authors: X
authors: He
authors: D A
authors: DA
authors: Yablonskiy
mesh_terms: D000465:Algorithms; D000818:Animals; D056324:Diffusion Tensor Imaging / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009900:Optic Nerve / Q000033:anatomy & histology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D066127:White Matter / Q000033:anatomy & histology*
references: Neuroimage. 2009 Jun;46(2):345-52
references: 19254768
references: Magn Reson Med. 2010 Jun;63(6):1471-7
references: 20512849
references: Magn Reson Med. 2008 Oct;60(4):882-8
references: 18816808
references: Neuroimage. 2009 Feb 15;44(4):1259-66
references: 19027861
references: NMR Biomed. 2013 Aug;26(8):963-86
references: 22927123
references: Magn Reson Med. 2001 Apr;45(4):533-42
references: 11283978
references: Proc Natl Acad Sci U S A. 2010 Feb 23;107(8):3834-9
references: 20133720
references: Magn Reson Med. 2000 Apr;43(4):491-6
references: 10748422
references: Magn Reson Med. 2011 Jan;65(1):35-43
references: 20928888
references: Proc Natl Acad Sci U S A. 2012 Nov 6;109(45):18559-64
references: 23091011
references: J Magn Reson. 2010 Jan;202(1):102-8
references: 19879785
references: NMR Biomed. 1989 Nov;2(4):151-60
references: 2641496
references: Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13558-63
references: 19628691
references: Proc Natl Acad Sci U S A. 2007 Jul 10;104(28):11796-801
references: 17586684
references: Magn Reson Imaging. 1992;10(4):597-608
references: 1501530
references: NMR Biomed. 2011 Apr;24(3):246-52
references: 21404336
references: Magn Reson Med. 1990 Feb;13(2):239-62
references: 2156125
references: Magn Reson Med. 2012 Jan;67(1):110-7
references: 21630352
references: Neuroimage. 2012 Feb 1;59(3):1979-87
references: 21985911
references: Neuroimage. 2010 Apr 1;50(2):491-8
references: 20026280
references: J Magn Reson Imaging. 2003 Sep;18(3):284-90
references: 12938122
references: Ann Neurol. 2008 Dec;64(6):707-13
references: 19107998
references: AJNR Am J Neuroradiol. 2005 Apr;26(4):736-42
references: 15814914
references: Neuroimage. 2011 Jun 1;56(3):930-8
references: 21320606
references: Proc Natl Acad Sci U S A. 2012 Aug 28;109(35):14212-7
references: 22891307
references: Neuroimage. 2012 Apr 2;60(2):1073-82
references: 22305993
references: Magn Reson Med. 2007 Jan;57(1):115-26
references: 17191227
references: Magn Reson Med. 2014 Mar;71(3):1251-63
references: 23637001
references: Magn Reson Med. 2014 Jan;71(1):345-53
references: 23382087
references: Proc Natl Acad Sci U S A. 2010 Mar 16;107(11):5130-5
references: 20202922
references: Neuroimage. 2010 Jan 1;49(1):193-8
references: 19619663
references: Neuroimage. 2012 Jan 16;59(2):1413-9
references: 21893208
references: Neuroimage. 2008 May 1;40(4):1561-6
references: 18353683