title: Improved shimming for fMRI specifically optimizing the local BOLD sensitivity.
abstract: In functional MRI, magnetic field inhomogeneities due to air-tissue susceptibility differences may lead to severe signal dropouts and geometric distortions in echo-planar images. Therefore, the inhomogeneities in the field are routinely minimized by shimming prior to imaging. However in fMRI, the Blood Oxygen Level Dependent (BOLD) effect is the measure of interest, so the BOLD sensitivity (BS) should be optimized rather than the magnetic field homogeneity. The analytical expression for an estimate of the BOLD sensitivity has been recently developed, allowing for the computation of BOLD sensitivity maps from echo-planar images and field maps. This report describes a novel shimming procedure that optimizes the local BOLD sensitivity over a region of interest. The method is applied in vivo and compared to a standard global shimming procedure. A breath-holding experiment was carried out and demonstrated that the BS-based shimming significantly improved the detection of activation in a target region of interest, the medial orbitofrontal cortex.
authors.affiliation: Cyclotron Research Centre, Liège University, Liège, Belgium. e.balteau@ulg.ac.be
authors.forename: Evelyne
authors.initials: E
authors.lastname: Balteau
authors.forename: Chloe
authors.initials: C
authors.lastname: Hutton
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Weiskopf
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000706:statistics & numerical data; D010100:Oxygen / Q000097:blood*; D015656:Respiratory Mechanics / Q000502:physiology; D012984:Software
chemical_list: D010100:Oxygen
references.citation: Magn Reson Med. 2002 Oct;48(4):715-22
references.pmid: 12353290
references.citation: J Neurosci. 2009 Feb 11;29(6):1648-56
references.pmid: 19211872
references.citation: Magn Reson Med. 2003 Mar;49(3):409-16
references.pmid: 12594742
references.citation: MAGMA. 2008 Mar;21(1-2):31-40
references.pmid: 18180969
references.citation: Magn Reson Med. 1999 Aug;42(2):290-9
references.pmid: 10440954
references.citation: PLoS One. 2009;4(3):e5091
references.pmid: 19333398
references.citation: Hum Brain Mapp. 2002 Nov;17(3):143-55
references.pmid: 12391568
references.citation: Neuroimage. 2001 May;13(5):903-19
references.pmid: 11304086
references.citation: Neuroimage. 2005 Mar;25(1):112-21
references.pmid: 15734348
references.citation: MAGMA. 2007 Feb;20(1):39-49
references.pmid: 17268781
references.citation: J Magn Reson. 2000 Aug;145(2):184-91
references.pmid: 10910686
references.citation: Stroke. 1998 Dec;29(12):2641-5
references.pmid: 9836778
references.citation: Neuroimage. 2006 Nov 1;33(2):493-504
references.pmid: 16959495
references.citation: Magn Reson Med. 1997 Mar;37(3):331-5
references.pmid: 9055220
references.citation: Neuroimage. 2005 May 15;26(1):243-50
references.pmid: 15862224
references.citation: Neuroimage. 2002 Jan;15(1):120-35
references.pmid: 11771980
references.citation: Magn Reson Med. 2008 Jan;59(1):221-7
references.pmid: 18050341
references.citation: Magn Reson Med. 1999 Jul;42(1):110-7
references.pmid: 10398956
references.citation: Magn Reson Med. 1991 Jul;20(1):113-22
references.pmid: 1943653
references.citation: Magn Reson Med. 1991 Apr;18(2):335-47
references.pmid: 2046515
references.citation: Magn Reson Med. 2005 May;53(5):1046-54
references.pmid: 15844094
references.citation: Magn Reson Med. 2001 Apr;45(4):595-604
references.pmid: 11283987
references.citation: Magn Reson Med. 1996 Jul;36(1):159-65
references.pmid: 8795035
references.citation: Magn Reson Med. 1993 Jun;29(6):804-11
references.pmid: 8350724
references.citation: Neuroimage. 1995 Sep;2(3):173-81
references.pmid: 9343600
references.citation: J Magn Reson Imaging. 1999 Apr;9(4):531-8
references.pmid: 10232510
references.citation: Neuroimage. 2002 May;16(1):217-40
references.pmid: 11969330
references.citation: Neuroimage. 2002 Oct;17(2):967-76
references.pmid: 12377170
references.citation: Magn Reson Med. 2001 Oct;46(4):631-7
references.pmid: 11590638
references.citation: Neuroimage. 2003 Jun;19(2 Pt 1):430-41
references.pmid: 12814592
references.citation: Magn Reson Imaging. 2001 Jan;19(1):13-20
references.pmid: 11295341
references.citation: Magn Reson Med. 2005 Aug;54(2):373-85
references.pmid: 16032676
references.citation: Neuroimage. 2004 Feb;21(2):757-67
references.pmid: 14980579
references.citation: Magn Reson Med. 1996 Mar;35(3):346-55
references.pmid: 8699946