title: Studies of RF Shimming Techniques with Minimization of RF Power Deposition and Their Associated Temperature Changes.
abstract: In ultrahigh field (UHF), human magnetic resonance imaging (MRI) concerns related to the homogeneity of the B1+ field [the radiofrequency (RF) magnetic field component responsible for the excitation of the spins] and the local/average specific absorption rate (SAR) are highly evident. In this work, through RF shimming techniques, a full-wave electromagnetic model that treats a coupled-RF coil and the load (an 18-tissue anatomically detailed human head model) as a single system is utilized to simultaneously (1) improve the homogeneity of B1+ field in various regions of interest across the volume of the human head and (2) minimize the total RF power deposition at 7 and 9.4 T. The numerical results illustrate that the B1+ field homogeneity (evaluated by the coefficient of variance) can be greatly improved in 3D slabs that vary in orientations and sizes, in the brain, and in the entire head volume without increasing the total RF power deposition in the head to exceed that obtained with quadrature excitation. The RF shimming simulation results are experimentally validated (by performing RF shimming without experimental B(1) measurements) on a head-sized phantom using a 7-T human MRI scanner equipped with a transmit array excitation system. The SAR and associated temperature changes under quadrature and RF shimming excitation conditions are calculated and compared.
authors: The Cooperative Institute, Mesoscale Meteorological Studies, The University of Oklahoma, Norman, Oklahoma 73072.
authors: Lin
authors: L
authors: Tang
authors: Yik-Kiong
authors: YK
authors: Hue
authors: Tamer S
authors: TS
authors: Ibrahim
references: Magn Reson Med. 1998 Dec;40(6):847-56
references: 9840829
references: Magn Reson Imaging. 2001 Dec;19(10):1339-47
references: 11804762
references: Magn Reson Med. 1984 Sep;1(3):339-53
references: 6571563
references: Magn Reson Med. 2006 Apr;55(4):883-93
references: 16508913
references: Magn Reson Med. 2008 Dec;60(6):1422-32
references: 19025908
references: J Magn Reson Imaging. 2008 Nov;28(5):1303-8
references: 18972342
references: IEEE Trans Biomed Eng. 2005 Jul;52(7):1278-84
references: 16041991
references: Magn Reson Med. 1986 Oct;3(5):722-9
references: 3784889
references: NMR Biomed. 2007 Feb;20(1):58-68
references: 17006885
references: Magn Reson Med. 2005 Jun;53(6):1251-7
references: 15906277
references: Magn Reson Med. 2005 Dec;54(6):1327-32
references: 16270331
references: J Magn Reson Imaging. 2004 May;19(5):650-6
references: 15112317
references: Magn Reson Med. 2001 Apr;45(4):692-9
references: 11283998
references: IEEE Trans Biomed Eng. 1998 May;45(5):650-9
references: 9581064
references: J Magn Reson Imaging. 2000 Jul;12(1):30-6
references: 10931562
references: Magn Reson Med. 2005 Feb;53(2):434-45
references: 15678527
references: NMR Biomed. 1988 Jun;1(3):151-8
references: 3275125
references: J Magn Reson Imaging. 2007 Jun;25(6):1235-47
references: 17520721
references: Med Phys. 1992 Jul-Aug;19(4):1089-98
references: 1518472
references: Phys Med Biol. 2001 Oct;46(10):2545-55
references: 11686274
references: IEEE Trans Biomed Eng. 1996 Jan;43(1):88-94
references: 8567009
references: Magn Reson Med. 1994 Aug;32(2):206-18
references: 7968443
references: NMR Biomed. 1998 Oct;11(6):263-5
references: 9802467
references: Magn Reson Med. 2001 Jul;46(1):24-30
references: 11443707
references: Magn Reson Med. 2007 Feb;57(2):235-42
references: 17260366
references: IEEE Trans Biomed Eng. 2006 May;53(5):963-7
references: 16686420
references: IEEE Trans Biomed Eng. 2003 Mar;50(3):295-304
references: 12669986
references: Magn Reson Med. 1997 Dec;38(6):953-63
references: 9402197
references: Magn Reson Med. 2005 Sep;54(3):683-90
references: 16088934
references: J Magn Reson Imaging. 2000 Jul;12(1):46-67
references: 10931564
references: J Magn Reson Imaging. 2003 Sep;18(3):383-8
references: 12938138
references: Magn Reson Med. 2007 Mar;57(3):577-86
references: 17326185
references: Ann Biomed Eng. 2007 May;35(5):825-34
references: 17334681
references: Phys Med Biol. 2001 Feb;46(2):609-19
references: 11229737
references: Magn Reson Med. 1999 Jul;42(1):183-92
references: 10398965
references: Magn Reson Med. 2001 Apr;45(4):684-91
references: 11283997
references: Magn Reson Imaging. 2005 Jan;23(1):53-60
references: 15733788
references: J Magn Reson Imaging. 2007 Aug;26(2):437-41
references: 17654736
references: Phys Med Biol. 2007 Sep 7;52(17):5429-41
references: 17762096
references: J Magn Reson Imaging. 2000 Jul;12(1):68-74
references: 10931565
references: Magn Reson Imaging. 2000 Jul;18(6):733-42
references: 10930783
references: Magn Reson Med. 2000 Nov;44(5):692-700
references: 11064403
references: IEEE Trans Biomed Eng. 2004 Aug;51(8):1301-9
references: 15311814