title: 7 Tesla MRI with a transmit/receive loopless antenna and B1-insensitive selective excitation.
abstract: OBJECTIVE
  Use of external coils with internal detectors or conductors is challenging at 7 Tesla (T) due to radiofrequency (RF) field (B1 ) penetration, B1 -inhomogeneity, mutual coupling, and potential local RF heating. The present study tests whether the near-quadratic gains in signal-to-noise ratio and field-of-view with field-strength previously reported for internal loopless antennae at 7T can suffice to perform MRI with an interventional transmit/receive antenna without using any external coils.
  
  
  METHODS
  External coils were replaced by semi-rigid or biocompatible transmit/receive loopless antennae requiring only a few Watts of peak RF power. Slice selection was provided by spatially selective B1 -insensitive composite RF pulses that compensate for the antenna's intrinsically nonuniform B1 -field. Power was adjusted to maintain local temperature rise ≤1°C. Fruit, intravascular MRI of diseased human vessels in vitro, and MRI of rabbit aorta in vivo are demonstrated.
  
  
  RESULTS
  Scout MRI with the transmit/receive antennae yielded a ≤10 cm cylindrical field-of-view, enabling subsequent targeted localization at ∼100 μm resolution in 10-50 s and/or 50 μm MRI in ∼2 min in vitro, and 100-300 μm MRI of the rabbit aorta in vivo.
  
  
  CONCLUSIONS
  A simple, low-power, one-device approach to interventional MRI at 7T offers the potential of truly high-resolution MRI, while avoiding issues with external coil excitation and interactions at 7T.
authors: Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland, USA; Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University, Baltimore, Maryland, USA.
authors: M Arcan
authors: MA
authors: Erturk
authors: AbdEl-Monem M
authors: AM
authors: El-Sharkawy
authors: Jay
authors: J
authors: Moore
authors: Paul A
authors: PA
authors: Bottomley
mesh_terms: D000818:Animals; D001011:Aorta / Q000033:anatomy & histology*; D003198:Computer Simulation; D004867:Equipment Design; D005240:Feasibility Studies; D007089:Image Enhancement / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D011817:Rabbits; D011846:Radio Waves
keywords: high-resolution MRI; in vivo interventional MRI; intravascular MRI; transmit/receive coils; vessel wall imaging
references: Magn Reson Med. 2001 Apr;45(4):692-9
references: 11283998
references: NMR Biomed. 2011 Apr;24(3):299-306
references: 20925128
references: J Magn Reson Imaging. 2005 Apr;21(4):463-7
references: 15779027
references: NMR Biomed. 2011 May;24(4):358-65
references: 20960577
references: Magn Reson Med. 2006 Dec;56(6):1274-82
references: 17075852
references: J Magn Reson Imaging. 2000 Jul;12(1):46-67
references: 10931564
references: NMR Biomed. 2013 Apr;26(4):436-42
references: 23074162
references: NMR Biomed. 2006 May;19(3):393-400
references: 16705630
references: Med Phys. 2008 May;35(5):1995-2006
references: 18561676
references: JACC Cardiovasc Imaging. 2010 Nov;3(11):1158-65
references: 21071004
references: Proc Natl Acad Sci U S A. 1997 Jul 8;94(14):7612-6
references: 9207140
references: Magn Reson Med. 2004 Apr;51(4):775-84
references: 15065251
references: Magn Reson Med. 2007 Mar;57(3):625-30
references: 17326167
references: Circulation. 2008 Dec 2;118(23):2368-73
references: 19015405
references: J Magn Reson. 2012 Jan;214(1):200-11
references: 22177383
references: Magn Reson Med. 2010 Dec;64(6):1625-39
references: 20740657
references: Magn Reson Med. 2004 Sep;52(3):590-7
references: 15334579
references: J Vasc Interv Radiol. 1998 Nov-Dec;9(6):953-9
references: 9840040
references: Catheter Cardiovasc Interv. 2005 Mar;64(3):265-74
references: 15736247
references: Magn Reson Med. 2012 Jul;68(1):311-8
references: 22127763
references: Magn Reson Imaging. 2001 Dec;19(10):1339-47
references: 11804762
references: Magn Reson Med. 2003 Jan;49(1):144-50
references: 12509830
references: Magn Reson Med. 2012 Sep;68(3):980-8
references: 22161992
references: Magn Reson Imaging. 2001 Feb;19(2):219-26
references: 11358660
references: Magn Reson Med. 2001 Jul;46(1):24-30
references: 11443707
references: Magn Reson Med. 1997 Jan;37(1):112-8
references: 8978639
references: J Magn Reson Imaging. 2005 May;21(5):546-55
references: 15834912
references: J Magn Reson. 2012 Jan;214(1):273-80
references: 22197502
references: Med Phys. 2009 Mar;36(3):908-19
references: 19378751