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7 Tesla MRI with a transmit/receive loopless antenna and B 1 ‐insensitive selective excitation
Author(s) -
Erturk M. Arcan,
ElSharkawy AbdElMonem M.,
Moore Jay,
Bottomley Paul A.
Publication year - 2014
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.24910
Subject(s) - radiofrequency coil , excitation , electromagnetic coil , nuclear magnetic resonance , biomedical engineering , physics , materials science , in vivo , rf power amplifier , antenna (radio) , radio frequency , signal (programming language) , magnetic resonance imaging , optics , acoustics , computer science , optoelectronics , telecommunications , medicine , radiology , cmos , microbiology and biotechnology , quantum mechanics , biology , programming language , amplifier
Purpose Use of external coils with internal detectors or conductors is challenging at 7 Tesla (T) due to radiofrequency (RF) field (B 1 ) penetration, B 1 ‐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 B 1 ‐insensitive composite RF pulses that compensate for the antenna's intrinsically nonuniform B 1 ‐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. Conclusion 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. Magn Reson Med 72:220–226, 2014. © 2013 Wiley Periodicals, Inc.